Radiant Heat Floor Mistakes FAQs

Q&A on radiant heated floor SNAFUs

Radiant Heat Installation Inspections

Your description of the installation of the radiant heating system by an uninformed contractor is typical.

The above description of the installation of the radiant heating system by an uninformed contractor (at RADIANT HEAT MISTAKES ) is typical.

Contractors in general do not understand heat or the design of a heating system. I live in Wisconsin and built a 24 X 40 foot building with in floor radiant heat. I used 2 inch rigid insulation under the slab and 1 inch rigid insulation on the perimeter of the slab. I used 1/2 inch PEX and a 35,000 BTU water heater for the heat source.

I designed and installed the system myself and it heats the building comfortable in below zero weather. I took pictures as I installed the system then wrote an installation guide I sell through Amazon.

I am a builder and a structural engineer so I was able to do all the necessary calculations for the design. I think radiant heating is great. It is quiet, efficient and simple. On 2016-05-12 03:20:02.382922 by CJ

by (mod)

Thanks CJ. I'd like to see photos of a "correct and successful" radiant heat slab. (Email is at page bottom CONTACT link)

You are dead right that the builder described in the article above (I call his company "Nightmareworks Construction" a variation of its actual name) didn't know radiant heat; worse his ego and pride got in his way - he'd never admit not knowing something and bullied his way through being questioned. He doesn't know that he doesn't know.

Some guys just keep making the same mistake over and over. Me I don't repeat the mistakes, but my boss told me he thought I intended to make them all once.

Where do I find an inspector for a radiant heated floor slab?

Looking to buy an older home that has radiant heat in a poured slab over the basement and powered by a new boiler system. I am concerned about finding a pre-purchase inspector that can adequately evaluate the system. Any suggestions on locating a competent inspector to examine the system? Thanks On 2022-08-09 by Lance

by InspectApedia (mod) - what to look for when inspecting a radiant heat floor system

@Lance,

You can start with our

HOME INSPECTORS DIRECTORY

Let us know if you have additional questions.

And ask the inspector if he or she is familiar with radiant heated slab systems and listen to how that person will evaluate the system operation.

There are some advantages if you can do the inspection when the weather is cold.

For example the inspector might use thermal scanning to check the floor areas.

How do I get my radiant heated floor home inspected?

I’m under contract on a 3000sf home in Manistee Michigan that was built in 1992 and I’m looking for someone qualified to inspect the radiant heat system. My inspection period starts on next Monday May 17, 2021 and ends 14 day later.

Do you know of a resource of qualified contractors or inspectors that I could utilize? In lieu of a list of qualified contractors, might you have a list of questions I can use to screen the contractor myself?
On 2021-05-13 by Anonymous
Also, I understand that early on when radiant slab systems were being install that poor tubing was used in some instances. Is this the case and how can I identify this tubing?

by danjoefriedman (mod) - points to consider in a competent onsite radiant heat system inspection

A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone, as we haven't a shred of information about your radiant heat design, location, climate, building etc. You will find additional depth and detail in articles at our website.

That said, I have these comments:
First, sorry, no I don't have a referral;

You should of course ask the contractor what is their experience with installing and fixing radiant heat systems.

Or read our articles on radiant heat failures and listen for some of that same mistaken thinking.

In particular take a look at

RADIANT HEAT CONTROLS
RADIANT HEAT DEFECTS LIST
RADIANT HEAT INSTALLATION
RADIANT HEAT MISTAKES
RADIANT HEAT TEMPERATURES
RADIANT SLAB FLOORING CHOICES

Live links for all of those articles are found at the Recommended Articles list at the end of the article above.

Often all you really need to do is ask even the most simple questions like: what are the important inspection points on a radiant heat floor system? Listen for: tubing routing, spacing, location, depth in slab, insulation below slab, slab perimeter insulation, controls, heat source, balancing, zone control.

The manufacturer of your tubing and heater and controls will, of course, have installation specifications that are worth your attention.

About your question about defective radiant heat tubing products,

See our discussion of "Plumb-Pex defective component installations in North America" included

in PEX PIPING INFORMATION

Radiant Heat Job Builder Disputes

Contractor omitted radiant heat tubing in bathroom

I'm putting in slab hydronic radiant floor in new construction basement. My contractor did not run tubing in my bathroom saying that there's enough tubing in the rest of the flooring that the bathroom floor will only be about 1 degree less than the rest of the flooring. Should I have him run the tube in the bathroom? On 2021-07-10 by Anonymous

by inspectapedia.com.moderator - where should radiant tubing be laid - bathroom is high priority

@Anonymous,

We don't know the construction, dimensions, layout of your home - details one would need to make a technically-confident reply to your question, but in general bathrooms are places where people most like a warm floor as that's where we're barefoot and standing on tile, not warmer wood or other surfaces.

Depending on the layout of your bathroom, I'd at least like to have radiant heat under the walking-on part of the floor and might omit it under a vanity and certainly not close to the sides of a toilet;

so if it were my bath I'd include radiant heat the wider most-walked-on area of the floor.

Builder claims radiant slab moisture is my fault because I used bad concrete. I say his tubing weeps moisture.

I installed thermal bluestone on top on 4" of concrete which has radiant heating tubing throughout. The large patio is under a covered porch.

The problem seems to be that there is moisture coming up to the surface of the thermal bluestone causing staining. Is it possible that the radiant heating tubes give off moisture/ condensation which causes the bluestone to absorb the moisture.

Another patio was constructed in the same manor but is in full sun around a pool. There is no staining and the thermal bluestone looks beautiful. Any advice or thoughts?

Builder claims its my fault because I used bad concrete. I blame builder that his installed tubing is holding moisture and being "sucked upwards" through the bluestone. Any thoughts? On 2020-05-22 by DJW

by (mod) - radiant heat tubing doesn't emit moisture unless it's leaking

DJW

The radiant tubing would only be expected to actually "give off" moisture if it has a leak - something you can track using infra red or a thermal scanner.

We also sometimes find water coming up through a slab from inadequate site or slab drainage at time of installation or later if roof or surface runoff are not directed away from the building.

The tubing materials themselves, either copper or PEX or something similar, do not absorb, hold, nor give off moisture.

How old are the concrete slab and the bluestone installation?

How long after initial installation was the radiant tubing turned on and heated?

I ask because there could certainly have been high moisture in the concrete itself, now being driven out by heat from the tubing,

or


there could be water coming up through the slab from water below it.

Radiant Heat Floor / Slab Damage Prevention

Can radiant heat tubing be left with the heat off without damage

Can one install heat tubing in a concrete floor and leave it not heated and not covered over the winter without damaging the system? On 2019-10-23 y Anonymous

by (mod) -

Well yes and no, Anon.

Yes: The tubing, empty or filled with antifreeze solution will not harm the floor when heat is left off.

No: when a building is left un-heated, depending on the climate, freezing temperatures, site preparation, soil moisture, and extent of building exposure to the weather, a foundation or slab can be damaged by frost heave, frost push, frost lensing if a building is left un-heated unless adequate measures were taken, such as surrounding the foundation by insulating foam, during construction.

But there may be other things to worry about in your building if you're leaving it with no heat in a freezing climate.

Detailed advice is

at WINTERIZE - HEAT OFF PROCEDURE 

If I turn the heating in the floor off could the frost get into the concrete and heave it up

If I turn the heating in the floor off could the frost get into the concrete and heave it up On 2020-03-27 by Janine

by (mod) - possibly

Possibly, Yes, Janine, depending on

- the amount of water in soil below the slab

- the outdoor temperature

- the duration that heat is left off

- the slab construction details: reinforcement, drainage, insulation, thickness, soil conditions below the slab

Radiant Heat Floor Not Warm Enough or Too Expensive

Tip: See RADIANT HEAT TEMPERATURES

Radiant heat floor does not heat adequately - 2-year battle to fix radiant heating floor system that doesn't keep up in cold weather

I have a in floor heating system that we have been battling with for 2 years. The only time that it will heat up the floor is when the outside temp is warmer outside. The system cannot keep up heating when it is cold outside. Is it possible that insulation was missed.

The plumber cannot figure out the problem and is close to washing his hands of it. 2015/11/06 Melissa said:

Reply:

Yes, Melissa, certainly there could be missing or inadequate insulation. Have you done a thermal scan of the floor?

Melissa said: what will thermal imaging show on a radiant heat floor?

We have not done thermal imaging, but what exactly would that show, or should we be looking for if we are able to do it?

Additional information. Let's say we set the thermostat at 24 deg Celsius The thermostat will activate the pump and will send hot water into the floor. The pipe at the tank is almost too hot to touch. The tubes coming out of the floor are noticeably cooler. The temperature does not climb in the basement and therefore the thermostat never stops asking for heat. I have a few theories;

1) Improper insulation. The energy is lost before it has a chance to heat the slab and when the system loses too much energy the time it takes the tank to reheat the coil all is lost and the system starts from square one again, and this constantly repeats itself, and the system essentially continuously chases it's tail.

2) Pump is unable to circulate the hot water quick enough through the system, and is actually the reason why the system isn't able to stay ahead.

Our plumber wants to more the thermostat because he feels that the fish tank that is about 4 feet away may be pushing heat into the thermostat, confusing it. As well 4 feet below the thermostat is out fresh air vent, so the plumber feels that it may also be confusing the thermostat.

Thoughts?

Reply:

If you turn on and run up the heat the image will show hot and cold spots that might tell us that the layout was insufficient, the loops mis-run, that there's been a leak, or that there are sections that look uninsulated; a thermography scan of the building exterior can give similar information around the floor perimeter.

In the article above I document what happens in a cold climate if the insulation is incomplete or the tubing too deep in the slab.

Certainly you can test the plumber's idea by simply insulating the thermostat from the fish and from any warm air drafts but I doubt that's needed. It'd be appropriate IF the thermostat was turning OFF the heat - thus thinking that you're warm enough.

Melissa said:
We are hoping that the problem isn't the lack of insulation. Is there any other problems that we could try to troubleshoot? We have switched out the thermostat already. The new one behaves the same way as the first one. The pump is definitely pumping, and we have a pressure gauge on the system showing roughly 18 psi at return.

Reply:

I've suggested tubing too deep in slab and also tubing that runs through a too-cold section without proper insulation; you need to check the output and return temps at the boiler.

Melissa

Thank you so much for your replies. Unfortunately I think in the end we may discover that this system will never work. It has been a long drawn out battle to try and get the plumber to come, and the plumbers next solution was to shut the system off and pretend it was never there with no refund of our money.

We will bring in a different plumber and also look into the thermal imaging that you suggested. Thanks again!

Reply:

I would not abandon the radiant heat system before we have a clear list of everything that has been investigated - so that we can compare that with other ideas that need to be checked. It would be a shame to give up on an installed radiant heat system as "unrepairable" only to discover years later that a tiny switch on a circuit board was not set to the proper temperature range.

Melissa said:

I completely agree. I am hoping that the new plumber will be able to troubleshoot and try and figure out possible causes of why the system won't heat the slab. It seems like people who take a look at our system are completely baffled as to why it won't work.

When we first got the system it only worked for a few short months in the winter, but it did work at one time.

I am just worried that the the plumber that I am bringing in won't be able to figure anything out for us, in which we will be left with a very expensive system that just won't work. Anyway the plumber is coming in a few days so we shall see.

Reply:

Melissa:

As I often discover in longer discussions with clients or readers, more clues emerge. The fact that your radiant floor heat worked properly at one time suggests that (barring something odd like a rising water table) the concerns of a innate design or installation errors such as tubing too deep or insulation left out are pretty much squashed.

So it sounds more like a control problem or even a tubing damage or leak or obstruction.

Before bringing in a plumber let's do some detective work: get a detailed thermographic scan of the floor and of the perimeter of the bottom of the building in cold weather with the heat on.

Send me the results.

See THERMAL IMAGING, THERMOGRAPHY for an introduction to thermography and what to expect.

Radiant heat isn't warm enough, what can I do?

Have a radiant heat job in which my plumber used 3/8 pex there are 5 loops about 250’ per loop with I 1/12 mud job and tile can’t seem to get heat working properly what can I do ? On 2018-11-21 by Tom

Reply by (mod) -

I think I would start by confirming that I have had water flow through all of the tubing and then I would compare the input and output temperatures. If there's two big rapids maybe that I'm losing heat somewhere or that the flow rate is too slow.

Can over-heated water damage radiant heat tubing?

Will over heated water (180 degrees ) cause damage to concrete slab poly piping - On 2017-01-23 by Al -

Reply by (mod) - yes over heated water (180 degrees ) will cause damage to concrete slab poly piping

Yes, polyethyelen tubing has temperature limits to which it can be exposed without damage

See

RADIANT HEAT TEMPERATURES

and also

temperature-related leaks discussed

at RADIANT SLAB TUBING LEAKS

Radiant Heat System Design / Installation Options: Slab thickness, Insulation,

Double layer of R10 under the Concrete slab and then the installation of the new PEX Uponor "Fast Trak" tubing system,

I found your article very interesting and educational especially since I am considering in-floor heating and trying to find out all pertinent information to do a good installation. I live in an area where the temps can drop to -40C, (-40F).

My plan was to put in the proper footing with maybe a one foot outside wall and then construct the walls up from there, thereby leaving room inside the short wall to install the PEX system. I need the home to be easy access with no stairs.

Would a double layer of R10 under the Concrete slab and then the installation of the new PEX Uponor "Fast Trak" tubing system, which in itself has insulation.

Do you think this new system will work well enough to give me the warm floors I want in an extremely cold climate?

I will be heating with a boiler system with a separate hot water tank for household use. On 2015-01-14 by Joyce

by (mod) - radiant heat floor workmanship is important

Joyce

Indeed I like radiant heat floors provided the workmanship gives a successful job.

It's not just the quantity of insulation - R20 might be fine - under the slab. It's watching out for other mistakes that cause the system to work poorly.

- be sure there is a thermal break at slab edges between indoors and outdoors

- be sure the tubing is high enough in the slab

- be sure the insulation is continuous under the slab

Compare adding radiant heat to a slab vs. baseboard vs floor covering choices

I really appreciate this site. Lots of great info here. I can't seem to find an answer to my issue concerning radiant floor heat and thought maybe you would have some insight.
I live in SE PA.

Where we can get sub zero temperatures during the winter months, It usually stays cool enough to need heat from late Oct until as late as the end of April.

I live in a Cape Cod style home using baseboard hydronic heat and an oil furnace designed sometime in the mid 70's. I augment the hydronic oil heat with a heat pump I installed myself. When the temps are in the 30"s I use the heat pump. If it gets colder I switch to the oil heat.

At the time I had my patio out back poured I decided to have a large portion of it poured with footers for future construction.

Fast forward a few years and it's time to add an addition to the footered concrete slab. Unfortunately I never considered the implications of not adding insulation under my slab. I also added a garage with a concrete pour that will have a studio at the back.

I did manage to get 2" foam insulation under that entire slab. I only wish I had known how important the insulation step was.

The addition is under roof and I'm now looking at my options for heat and cooling in that space. I really like what I read about radiant floor heat, yet I have a few concerns. One real advantage I have is my floor has over 5 inches to door openings.

I have a LOT of working room concerning insulation. Grade and moisture migration are almost nil since my slab is slightly above grade not including the additional height I can gain on my floor. The perimeter of my room is 8" insulation filled block at three courses above grade. 2x6 framing from there.

One side of the room is part of the garage wall. The back, of course, is all against the house, so I have two fully exposed exposed walls with lots of glass and 14' cathedral ceiling. Room size 24x14 . Hopefully this gives you some idea of the circumstances in needing to heat the space.

My boiler sits just behind addition room in the basement.

Since I have about 5 inches between the concrete floor and the doors I am toying with the idea to lay two sheets of 2" foam insulation on the floor. The insulation is load bearing and should support furniture if an additional flooring or plywood base is added.

I would add perimeter insulation around the block going up three courses. The only caveat is I think ceramic tile flooring will be too unforgiving, leaving me with hard wood or laminate as my choices.

In a basement this would be bad news, but above ground this seems like a solid approach, however I don't really know and before I spend all that money I wanted to ask around.

Some things about hydronic radiant heat tied to a boiler seem counter productive to me. Mainly building up a 160-180F temperature and then reducing it to 85-125F.

The recovery times etc. I would need a hybrid system since the rest of my house is straight baseboard heat which works well BTW even in my 70's insulated home.

The cost outlay to use a lot of 2"foam at about 30.00 a sheet here plus the cost of the pex and piping arrangement to temper the water to probably less than 100F will probably be steep .vs me simply running baseboard heat along the long wall under the windows and putting it on a separate loop/t-stat.

In that case I don't need to temper the water.

Do you see flaws in my thinking here? I am a career hvac guy but I was mostly in refrigeration.

I have put in boilers back in the day. I service my own equipment. I knew the importance of insulation, but I let this one get by me.

Back when I did the pour I should have made sure the contractor added insulation. I made an assumption. You know what happens when we assume. By the time the pour was done, it was too late. On 2018-05-22 by Tim

by (mod) - add a layer of insulating foam before adding flooring

Tim

This companion article is worth reading SLAB INSULATION, RADIANT / PASSIVE SOLAR https://inspectapedia.com/Energy/Slab_Insulation.php

For your application I like foil-faced high-R foam board insulation, since the reflective barrier may give a small additional benefit.

In some states and provinces building codes don't require sub-slab insulation except for those in very cold climates. But as you read above, the heat loss down through a slab in colder areas including the northeastern US such as PA, can be quite significant.

You're fortunate if your existing structure permits, as you suggest, adding a layer of insulating foam followed by a new layer of flooring. I agree that ceramic tile over a floor that flexes would be a disaster.

If you wanted tile in preference to a laminate or engineered wood floor, or in preference to a vinyl tile floor (those would typically be problem free), and if you can give up the additional 1 1/2" of space for double underlayment, you could perhaps use ceramic tile over a double layer of 3/4" solid core underlayment placed atop your foam slabs that are in turn atop concrete. I'd discuss that option with your tile supplier to get a local opinon.

Where I've seen such retrofit floor get into trouble, aside from flexing and cracking tile that we've aside for now, it has been the mold and rot that occur if water leaks into that floor structure.

Trapped there the water leads to damage, rot, mold, and sometimes insect attack.
With your floor above grade those risks are considerably lower than if the floor were in a basement.

Your concern for the build-up, reduce-down operating temperatures of radiant floor heat, if I understand it correctly, should be mitigated by a review of just how radiant heat systems operate. Because we don't want the floor to be uncomfortably hot (and also because high temperatures can damage some tubing types), a mixing valve keeps the water circulating in the floor at or below a safe temperature limit.

But we like to operate the boiler at a higher temperature for operating efficiency and thus lower heating cost.

That mixing valve automagically handles the problem by mixing in with the circulating water in the floor just enough hot water from the boiler.

The efficiency gain is in fewer on-cycles at the boiler and higher boiler operating temperature. AQUASTAT HI LO DIFF SETTINGS offers more detail.

by Tim - steps to control moisture & water entry & report of leaks during construction

Thank you this info. The additional article links have been most helpful.

I had never considered using a foil faced insulation. If I kept the foil away from the concrete this should help a lot.

I have kicked around the idea to use a concrete moisture sealer around the perimeter of the space to help mitigate any small amount of moisture that might get inside of the space.

We just had ten days of rain in a row here. My window openings were covered with Tyvek until the windows we ordered come in.

The only place moisture could come in would have been under the pour/around the footers. There was just the slightest dampness showing in one corner of the space.

No puddles, just a wet mark. I don't have it graded or spouting hooked up yet. I attribute that moisture to this.

Worse case scenario- maybe a big snow melt off in the Spring or another huge long period of rain causes some migration. Wouldn't heating the space remove those small amounts? Cooling in the summer should have a similar effect unless I'm missing something.

The house sits up on a small hill but not all the way on top. There is a grade behind the house. Drainage piping surrounding the perimeter of the footings tied to pipes for rain spouts and exiting from pipe buried underground 30' from origin of the water was supposed to help offset that. I considered a drain pit .

Still might be a future option. Township approved present layout. That very small damp place after 10 days of rain without the spouting hooked up doesn't strike me as a serious issue, so long as I can correct it with climate control.

I've been wrong plenty of times before though. What seems much more serious to me is if the pex develops a leak or if I had say, a roof leak that let water into the space which accumulated underneath the works. A foam floor would have the tendency to float. Ha.

I might have a boat in my room in addition to the mold. Two weeks running dehumidifiers might help to remedy such a bad situation.Hopefully I won't ever see that happen.

I really like your idea to use a thicker sub floor since 2" of good foam insulation is all that seems to be required. 4' might be overkill.Can't hurt I suppose. Does add to the expense. I would opt for ceramic tile, so I like your idea. I think tile would work best with a radiant floor.

Along the same lines as your foil face insulation idea, I could also obtain sheet metal, either aluminum or steel to roll out under the pex.

I'm considering a thin gauge. Probably less expensive that the pre made panels. Main consideration being a good way to hold tubing in place until the flooring is put on. Duct tape?

Another plus for ceramic floor is there are no staples, nails or screws put in the floor around the pex. That would make me nervous.

From what I read online hydronics mixing valves and associated gear needed to hook up a radiant heat system are much more expensive than a common baseboard convection heat system which is what I presently have.

From a cost standpoint I could save money if I went with hydronic baseboards, however I'm planning to replace my aging boiler soon myself, so I can be the labor which should save me a bundle. Money is a consideration here.

I am willing to spend more money for radiant heat if I can make it work and it isn't overly expensive as compared to my other options. I see it as a good resale value choice and a way to improve comfort in the space.

Once done any attempt to repair concrete poured pex isn't something I want to even think about. I would do all the right things, pressure test,add anti-freeze, keep my loop temps well below the pex limits.

I'm still a little apprehensive in looking at how dependable this is long term, but that's me.

by (mod) - water that leaks under the layers of a floor

Unfortunately if you have water that leaks under the layers of a floor constructed in the way that we have been discussing heating the building will not remove it. Water tends to be trapped in such areas for a long time and therefore to cause problems with mold or rot or insects.

All of the effort then needs to be making sure that we're constructing a floor that won't be subject to water leaks.

Why was your cabin floor slab so thick?

You say the tubing was seven to eighteen inches deep in the concrete. Why would you have such a thick floor in a cabin? - On 2018-05-07 by Don -

Reply by (mod) - Why would you have such a thick radiant heat slab floor in a cabin?

The floor shown at RADIANT HEAT MISTAKES was poured as part of a monolithic slab. The tubing was placed at the bottom of the pour.

The slab thickness was just about seven inches - entirely normal.

The 18-inch thickness in my article and that doubtless prompted your question, was the depth of the integral footing that was poured as part of the monolithic slab.

Unfortunately in some areas of the actual floor the excavator and contractor actually dropped the floor area of the slab and the radiant heat tubing as well as the wire mesh down to that deeper level.

Put down plastic under radiant heat tubing on Stone ?

Do I need to put plastic down on stone subgrade before foam and tubing goes in. My job is installing a floor heat system in a barn - On 2017-11-04 by Gary

Reply by (mod) -

Watch out: Plastic isn't the first question here. If you are putting radiant heat tubing on Stone which is in turn on dirt than your heating system probably will not work as more heat will be flowing down through Stone and soil than up through floor.

I would want solid foam insulation between my tubing and stone. That's more critical than the plastic barrier about which you asked.

Do I need a water softener for my radiant heat system?

adding water softener with 14 year old Radiant heating system good or bad idea ? - On 2017-03-06 by WILLIAM BERRY -

Reply by (mod) - Not normally

William

I don't think the softener will make much difference to how your radiant heating system is working, though it will reduce mineral scaling and clogging in other parts of the building water supply system, particularly the hot water heater and its piping.

That's because in most hydronic (hot water) heating system, regardless of their form as radiant heat tubing or radiators or baseboards, the same physical volume of water remains closed in the system, circulating around heated in response to heat.

Because new water is not constantly being added to a hydronic system, the total quantity of dissolved minerals in the water is limited and tends not to be a serious problem. (Steam heat is a different matter entirely).

Radiant Heat Boiler Questions

What do I use as a heat source for a small additional radiant heated garage slab?

I am adding a 16x24 bay with 2x4 construction and fiberglass insulation to an existing garage.

I want radiant heat in the floor but it`s only 385 sq`. Closed system. Glycol.

What do I use for heat source? I`ve been told on demand boilers wouldn`t work for such a small system. 1 zone, 2 loops of maybe 250 feet half inch pex. On 2019-07-12 by nelson

Reply by (mod) -

There are small electric heating boilers designed specifically for applications such as the one you described.

In our RADIANT HEAT MISTAKES article the boiler was a nice little Thermolec model.

You'll see one in the third photo down from the top of this article.

Some people also use electric water heater and there are some that are sold for that purpose.

However the duty cycle in my opinion is likely to give a short life for a water heater unless you're using a boiler designed for that purpose.

Weil-Mclain Ultra 230 Condensing Boiler setup for radiant heat

This boiler can handle three different setups with very different needs -- it does a prepurge and a postpurge when changing from one to the other.

All loops share a small boiler circulator that moves water through the boiler loop, but each other setup has it's own in-line pumps.

The "purge" appears to get the water in the boiler loop to an appropriate temp before switching from one demand to the other.

Our boiler is set with the DHW as priority 1, it has a target supply heat of 170, and the radiant heat as priority 2, target supply heat of 120; priority 3 is empty right now.

There is a separate cutoff in the feed line to the radiant heat loops (past the common boiler loop) that will shut the whole thing down if it hits 140 -- that's the overtemp protection.

This system is *smart*! It even has built in defaults for radiant heat slab VS radiant heat ceiling (as well as almost any kind of HWH you might want).

As the contractor and his crew learned about it, they taught us, since we had to play a bit with the supply target range to find the sweet spot that didn't overheat floors.

It took a long time, but boy do we have a nice setup now. The old unit was leading edge in 1952, the new unit is leading edge now.

Weil-Mclain Ultra 230 Condensing. They added some optional sensors, but the capability for the sensors is built into the base unit. On 2015-01-03 by Susan -

Reply by (mod) -

Thanks for the helpful feedback, Susan.

The notion that a condensing boiler is also moderating temperature to a radiant heat floor system is useful to learn about but a bit uncertain at least for cases in which a heating boiler is being used both for radiant heat flooring and other applications such as heating conventional radiators or baseboard (those want to be at a higher temperature than radiant floor tubing) or heating a tankless coil for domestic hot water.

Kudos to you and your contractor.

by Susan

Finally! The mixing valve was removed completely (Weil-Mclain says this is a condensing boiler and it does all the modulation, the mixing valve is not needed and was actually inhibiting flow); the pipes have been straightened out and several 1" lines are now 1.5"; and there's a proper overtemp cutoff in place on the floor loops.

The existing loops really do seem to be fine -- a sample of water was drawn for a repeat test of concentration for the X100 anti-corrosion agent, and the water was clean and clear.

And we can now run both pumps at once with flow of 5-7 GPM. The house is *evenly* warm now.

I think we're finally done! Just in time, 5-10 degree temps in the forecast.

Thank you for your time, Dan. Sites like this can help a *lot* - we were educated enough to understand what was going on, ask reasonable questions and help with the debugging process, and had a contractor who would work *with* us. As a partnership we got this resolved better and faster.

Why does my radiant heat floor boiler runs so much?

My floor heat boiler runs lots and cycles on the high limit switch of the boiler . 120 f max .

Then it cuts out and until it goes to110 fro cut back in .

If water temperature in is 15 degrees lower then water temp out And it cycles in the high limit switch of the boiler until the thermostat settings are met .

is this OK ? System is 50 years old but boiler is brand new On 2021-02-07 by Steve

Reply by (mod) -

Steve

If the boiler is cycling frequently it may be that a balancing or mixing valve in the radiant floor heat system is not set correctly. Ask your heating service tech to take a look and let me know what you are told.

by Steve

To add .. this is a open system.. not under pressure ..
When I use a temp gun to check the pad it’s running at about 23- 25 degrees C (73 -77f)

Thermostat is set at 17C ..
Should my pad be running hotter if water going through it is 110-120 as the boiler says it is ..

Is water going to fast that transfer is not effective?or is it OK the way it is ?
Had a hard time meeting thermostat needs in cold weather like -25 and lower etc

Reply by (mod) -

Pumping faster, with some subtle technical exceptions, puts more BTUs per minute into the floor;

Check the temperatures entering the floor loop and then returning out of it; you might see that there is a bigger drop than anticipated, hinting at heat loss into the ground at a rate not anticipated.

Hydronic floor heat (radiant heat) boiler cycles on-off every 2-12 minutes

I bought a home with hydronic floor heat (it was built in 1999). It's a one-story on a slab and has no basement. The system is one zone and serves the entire house (~1400 square feet) and the insulated 4-car garage. There is only one thermostat for it that I currently use as an off-on switch.

I've never before had a hydronic system and don't really know whether I'm operating it in the best way, and am hoping you can provide insight.

I currently have it set up to provide 80 degree water to the floor piping and run it 24 hours per day, 7 days a week starting in mid-October through April.

The boiler cycles, burning for about 2 minutes and is off for about 12 minutes - so the total burn time per day for the boiler is 4-5 hours. Is this a "good" operating scheme or would it be better to run the boiler constantly for two 2.5 hour intervals during the day, and increasing the water temperature water so the boiler is operating continuously?

Operating it as I do does keep the floors comfortably warm through the winter and the ancillary heat (electric forced air) only operates infrequently - usually when the outside temperature is at or below 0 degrees F.

Thank you for any help you can offer. On 2020-12-28 by John H -

Reply by (mod) - boiler may run nearly continuously in very coldest weather

John

That sounds perfectly reasonable to me. You may find that on the coldest days of the year your heater is running almost continuously but on other days it should be running at a much smaller percentage of the time just as you described.

For Radiant Heated Floors Is it better to run the boiler for longer intervals?

Thank you very much for the swift reply! I'm sorry but I'm utterly ignorant in this area so for clarification I have to ask - is it acceptable to have the boiler cycle on/off every 12 minutes or so as it currently does or is it not the best way to operate the system?

Would it be better to have it run continuously for longer periods of time? Or does it matter and either way is fine? Thank you again for your help and patience. :-) On 2020-12-29 by John H -

by (mod) - yes; here's what determines radiant heat boiler on-time in cold weather

When weather is colder, John, you would expect to see the boiler on for a longer interval;

Affecting the boiler cycle rate are a number of factors; to decide if it's behaving normally we ought to review those:

- outdoor temperature
- age and type of building - some idea of rate of heat loss
- presence of mixing valves and manifolds that recycle radiant heat floor water and keep it from reaching a too-high temperature
- setting of temperature for the floor loops
- settings on the boiler's aquastat itself: HI LO DIFF
- presence or absence of a domestic hot water tankless coil on the boiler
- boiler fuel: oil/gas
- temperatures seen on the boiler gauge (and pressure)

Generally a longer "ON" cycle is more-efficient; it takes about 5 minutes for a boiler to get up to full operating temperature.

Adding Radiant Heat to an Existing Slab or Floor

How best to add radiant heat atop an existing floor with no known insulation or vapor barrier

I read your fascinating article on installing radiant heat systems when pouring slab foundations;

however, I'm in the process of purchasing a house with an existing slab foundation, built in 1974, and no history of whether insulation or vapor barriers were installed at the time.

I'd like advice on how to add a radiant heating system on top of the floor, with the intention of replacing the flooring currently in place. On 2020-09-26 by Linda

by mod) - how to add a radiant heating system on top of an existing concrete slab floor

...

Linda

There are certainly radiant floor heat systems that can work perfectly well on top of a slab, covered by new flooring; the exact process and choices will depend on what kind of finish flooring is in mind and on the need for furring strips and a new layer of subfloor over the slab.

Those include hydronic radiant heat floor systems - tubing set atop the existing floor, over which a new floor is placed, perhaps using furring strips, subflooring, finish flooring, and electrical radiant heating systems that can be installed similarly.

Thin film radiant heat systems, other electric radiant heat floor systems as well as hydronic or hot water radiant heat flooring systems are described on this page and at the

RECOMMENDED READING links at the end of this article.

Shown here is ThermoSoft's electric radiant heating mat, sold in 15 square-foot sections and that is used under ceramic or stone tile finish flooring.

Start by asking for guidance from an **experienced** radiant heat floor installer in your area.

She may want to investigate under the slab to see what sort of insulation is there and if necessary she may want to add insulation before adding the radiant heat system.

Here are examples of electric radiant heat flooring systems

• ThermoSoft, Corporate Headquarters 701 Corporate Woods Pkwy Vernon Hills, IL 60061 Tel: 847-279-3800 Fax: 847-279-8845 www.thermosoftinternational.com info@thermosoft.com Tel: 855.819.3015 Email: info@thermosoft.com Website: https://www.thermosoft.com/docs/tt_install_guide.pdf This company has offices in Canada, Chile, the U.S., Germany, Russia, the UK, Slovakia, and Japan.
• Nuheat radiant floor heating cable
• WarmWire Radiant Floor Heating Cable Website: https://www.warmyourfloor.com
• Watts SunTouch, 4500 E. Progress Place, Springfield MO 65803 USA Tel: 888 4232-8932 Website: www.suntouch.com radiant heat flooring systems

by Linda

thank you for your rapid response. I'll contact an experienced radiant heat floor installer and pursue having the slab checked for insulation.