Aquastat High, Low, & DIFF FAQs

Heating boiler settings Q&A #3

Aquastat Settings to Improve Radiator / Baseboard Heat Output FAQs

How to get more heat to distant radiators

I have a oil hot water with radiator system It has the tankless hot water but I do not use it now If I have a power outage

I Have the furnace hooked up to run off a generator so I would then switch to the tankless water heat.

My question is what should the High/Low on the aquastat Honeywell LB124A,C LB151A be set.

My issue is that some radiators that are the farthest from the boiler do not get as hot as the others.

I have purged all air from the system.

The radiators closest to the boiler provide excellent heat - On 2016-12-11 by Choke51

On 2016-12-13 by (mod) - what should the High/Low on the aquastat Honeywell LB124A,C LB151A be set.

HI 180-200

LO 140-160

Running as hot as you can helps the distant radiators, as would insulating water heating lines.

Watch out: But running too hot - over 200, is unsafe.

Aquastat HI LO DIFF Accuracy FAQs

Monitor actual boiler temperatures to calibrate Aquastat HI LO DIFF settings

I think with the inaccuracies of the temperature sensing equipment, after setting 200hi, 180 low diff 25 (domestic max temp 195) one should monitor the boiler to make sure these temps are reached.

5degs is small buffer if there is inaccurate guage. On my setup i just noticed our "anti-scald" valve says (right on it!) "not anti-scald"

Just some random screw based temperature mixing valve. Very hard to know what temp it's set to. Just do it by feel... 120-160 range. Set roughly middle. Would a real one make for more stable temperatures?
Thank you, i learned a lot. On 2016-07-12 7 by Alex

Reply by (mod) - heating boiler gauge temperature reading accuracy

I agree, Alex, except I might add that monitoring the boiler temperature by its own gauge doesn't reassure me entirely: the gauge is also not precise lab-grade instrumentation. If you set the gap between HI and LO to a bit more than the 20 degF minimum then you can help assure there is no inadvertent lock-out of the boiler.

Lower temperatures waste fuel and thus are inefficient.

 

Aquastat Settings for Combination Wood-Oil Heaters or Backup Heat FAQs

HI LO DIFF settings on Aquastat on boiler used only for Backup Heat

Could use some guidance as my situation is very similar to this thread. Switch to heat pumps for both heating and a separate Heat pump HW system.

My oil furnace is now only for backup forced hot water backup heat on single digit and colder days.

I've left my aquastat hi/low at the summer values, which I thought were efficient (110/140).

Now I notice it takes longer for the backup heat to assist, but I'm ok with that as long as my oil consumption is lower/efficient. Did I miss the mark with these settings? On 2018-01-01 1 by Jim

by (mod) -

If your system uses an aquastat you have hydronic or hot water heat - properly called a boiler, though many people use the word "furnace" generically. (Furnaces are hot air systems) - just to be clear.

Now for a boiler, you'll get more efficient heat transfer by setting the aquastat HI up close to 200F as described at AQUASTAT HI LO DIFF SETTINGS - topic home.

by Jim

Thank you for the quick response! You are correct on your assumptions and my incorrect description.

Appreciate it very much and will use that guidance.

Aquastat Settings for Two Boiler System: Main & Backup

I have two boilers for my home heating system. The main system is an electric boiler that runs on a Dual Fuel system. When the Power company decides to turn off the electricity to the main boiler, the system switches over to my backup Oil boiler (Burnham).

The back up boiler is installed in my garage where the temperature is approx. 40 degrees in the winter.

I have tried to set the HI and LOW settings to not run if the house is not calling for heat. Sometimes the cooler temps in my garage will cool off the boiler water temps and want to come on, wasting oil consumption.

What would be the best HI/LOW temps for this situation. Knowing on occasion the Electrical power will be turned off for a few hours and the house might need the back up oil boiler to take over the task. Can I set the LOW on 100 and leave the HI on 180?

I'm thinking the lower limit may not be reached in a few hours of the Main boiler being shut off. Your thoughts? On 2017-09-23 by JIM

On 2017-09-24 by (mod) -

Jim,

As the LO it's only needed to work with a tankless coil for making domestic hot water, and as apparently you're not making that use of this boiler, you might want to disable the low function entirely.
this article series includes the description of how to do that.

Then you can set the high limit down as you suggest although there is some advantage to keeping a bit of heat in the boiler even when your house isn't calling for heat as it avoids rust corrosion and his damaged.

The fact is that if your house isn't calling for heat when they boiler cools off enough to turn on the burner the on cycle will be rather short because you're only heating the water in the boiler itself. The total cost of those Cycles would be quite small.

keep in mind that it's the inside thermostat in the heated portion of the house that's going to be responsible for turning the boiler on for a longer on cycle.

I actually prefer leaving my boiler set to 180 or 200 because that's more efficient way to operate a boiler when I'm running for heat and when my boiler doesn't include an automatic outdoor temperature compensating device.

Aquastat Settings for Wood Burning Heating Boiler tied into Oil Gired Heating Boiler Controls

Philip asked:

I have just installed an outside wood burning furnace that ties into my oil Furnace via a water to water heat exchanger. The wood furnace cycles Hot water constantly. When the house calls for heat the oil furnace turns on for about 5 minutes or longer. I assume this a result of the colder radiator Water cycling through the heat exchanger.

Once the oil furnace gets up to temp it stops and the wood furnace keeps up. I would like to have the Oil furnace burner not turn on at all. Can I unplug the connector from the Aquastat to the burner? And will the two circulating pumps still work for the Hot water and heat. (Oct 17, 2011) Phillip said:

Jeff said:

I have just installed an outside wood burning furnace that ties into my oil Furnace via a 30 plate water to water heat exchanger. The wood furnace cycles
Hot water constantly at 170. My aquastat settings are HI 130 LO 110 DIFF 10. I have tried to adjust the settings in many ways to eliminate the oil furnace from running at all, but have not been able to do this.

When the house calls for heat the oil furnace turns on for about 2- 5 minutes. I know this a result of the colder baseboard
Water and the reservoir in the oil furnace cooling between calls for heat. Once the oil furnace gets up to temp it stops and the wood furnace keeps up. There are times when the circulator pump runs without the furnace running which is ideal.

I would like to have the Oil furnace burner not turn on at all. I know I can unplug the connector from the
Aquastat to the burner or add a switch and the circulating pump will still work but I was hoping to achieve the never use oil system without having to do this.

What settings would you make for the HI, LO, DIFF and at what temperature would you run the wood furnace? If I bring the HI to 120 can there be be a 20 degree difference between the LO?
Thanks (Dec 7, 2011)

Reply:

Phillip:

I agree that the shot of cold water from the home's radiators will drop temperature in the boiler and cause its burner to turn on.

If the system is wired as usual, if you disconnect electrical power to the oil burner itself the circulator pumps will continue to function normally, Phillip. In fact one could install an electrical switch just for that purpose.

Just watch out: if you leave the burner off and also leave the home such that your wood burner runs down you'll risk frozen pipe damage.

Here's an alternative to consider:

Normally for boiler efficiency we like to set the aquastat HI to 200.

If your aquastat HI limit is set to 200 F (about as high as is safe), as long as the boiler temp stays above about 180F the burner won't come on until boiler water drops below that point. The burner "on" point is fixed at about 20 degF. below the HI (assuming you are not using a tankless coil for domestic hot water and the LO limit and DIFF have been disabled).

But if you temporarily drop the HI down to 120, the "ON" point will be around 100 - that too might prevent unnecessary boiler cycling when the wood burner is working.

If you do use a tankless coil and the aquastat's LO and DIFF are left in service be sure to also keep the LO set to at least 20 degF below the new HI setting.

(Oct 18, 2011) Phillip said:

Thanks DanJoeFriedman for the response. I have a one zone house with about 18 radiators. The amount of cold radiator water is quite large to cycle through the furnace. If I understand you correctly no matter what setting I use for the Hi/Lo and differential I would still expect that the oil furnace would kick in until the temp reached the diff limit. Today I set the hi to about 140 the low to 120 and the diff to 10 degrees.

My thought was that with the lo set at 120 the furnace would kick off at about 130 degrees and with the heat exchanger helping out heat the cold return water that that would minimize the amount of time the oil furnace is on.

Ideally I would like the oil burner to never kick on unless the wood furnace burns out or has a failure with its circulating pump. If there is no harm in just unconnecting the burner cable from the aquastat (there is a nice connector in the middle of the cable) then I might try that this weekend.

I can always reconnect during the cold months as a backup. So just to be clear on a typical installation there is no feadback to the Aquastat from the burner unit that would cause the Aquastat from not turning on the circulating pumps when there is a call fro heat from the house or the hot water tank?

Reply:

Not quite Phillip

Please review the explanation of HI LO DIFF

The boiler will start it's oil burner if on a call for heat at the thermosta the boiler temp is about 10F below the HI

The Lo and diff settings maintain heat in the boiler when there is no call for heating, in order to heat a tankless coil in summer.

I'm skipping details found in the articles on this topic.

 

Aquastat Settings for Pellet stove and SuperStor Water Heater

I have a pellet boiler tied into my oil burner and a super stor water heater. What do you recommend to have aquastat settings H,L DIFF on the oil burner set at so the 2 systems operate efficiently.

Right now the the oil burner kicks on and the pellet boiler doesn't ignite or still at a low burn rate because the unit is not calling for heat. Thanks for the help! On 2016-10-26 by Jesse

by (mod) -

Jim the flow rate of water into a tankless heater will determine if it turns on or not. Too-slow an inlet rate will keep the burner off.
Search InspectApedia

for TANKLESS WATER HEATERS for details.

Watch out: You can operate both at once but the output water temp may be too high and so risk scalding burns unless you also install a tempering valve.

Properly adjusted a demand or tankless water heater (not a tankless coil on a boiler) gives endless hot water at whatever temp you want. I would concentrate on solving the input pressure issue.

Aquastat Settings with No Tankless Coil FAQs

How to stop using the tankless coil

I stopped using the tankless coil for domestic water last year upon having a large external tank installed (smart 40 system).

I read AQUASTAT HI LO DIFF SETTINGS describing a disconnect of the low setting. Wouldn't that be a bad idea for winter heating as the house would call for heat and the furnace would run and run to try and bring the base boards up to temp.?

Also is there a more efficeint system or way to run my current system for winter.

As it is now with my Weil-McLain Oil Boiler at Hi 200 Low 160 my furnace runs almost every 15 minutes. Is that just the way it's supposed to work? Each new winter season I always seem to forget how much that thing runs and oil isn't getting any cheaper. (Oct 27, 2011) Marc Ruland said:

I have an old boiler in the house I just bought. It has a reckless coil for hot water. I notice that it turns on about 10 times a day for a few minutes at a time.

This happens even when the heat is off (during the summer and this fall). Is it turning on just to heat water? Seems like a lot to me.

On the recommendation of this article I changed the settings of the aquastat, but not sure if they are related. (Nov 17, 2011) Josh said:

Reply:

Take a look at the instructions found
in AQUASTAT LO & DIFF DISABLED if you want to abandon using a tankless coil

Use Tankless Coil to Pre-Heat Water Inlet to Electric Water Heater FAQs

Burnham oil boiler with a honeywell aquastat set at 180/160/20 diff

Nick said:

Currently I have a Burnham oil boiler with a honeywell aquastat set at 180/160/20 diff.

I am planning on installing an electric hot water heater in series with the boiler so that in the winter the coil is used to preheat the water coming into the electric hot water and in summer I can fully turn off the oil boiler and only rely on the electric hot water heater, thus using no oil but still having hot water. IN the winter, when I am using the boiler to heat the house- using copper/aluminum baseboards- what are going to be my best settings.

We tend to keep the house on the cool side, as this is a guest-house that isn't always occupied. We live in Maryland, so there are some very cold days, and some not so cold. My feeling is that settings along the lines of 190/120/25 diff might be good.

It seems that the low should be set very low- on a warm winter day where there is minimal call for heat, there is no reason to keep the water warm, and everything suggests that the high should be high with this type of baseboard as it is much more efficient at a high temperature.

My goal is to maximize efficiency, ie minimize oil usage. What are peoples' thoughts on this??? I'm unclear what my best diff setting is. Does the diff only effect the low?

On reading this, maybe more appropriate settings for me would be 190/120/10 diff. Thoughts? Feb 15, 2012)

Reply:

Buddy said:

Nick, I installed an electric water heater in parallel with my tankless water heater last year.

You can see my comments on January 12, 2012 on this web-site under "Guide to Heating System Boiler Aquastats (AQUASTAT CONTROLS) ,

Their Settings & Wiring." Installing your electric water heater in series after the tankless seems to makes sense since your hot water usage is probably relatively low.

My old settings were 190 hi/160 low/ 15 diff in order to ensure adequate domestic hot water temperature.

This winter I have my Aquastat set at the lowest possible, 130 hi/ 110 low/ 10 diff although the actual boiler temperature seems to run about 150 hi and 120 low.

I am using the electric water heater but not the tankless.

These settings have been adequate to re-heat the house with copper/aluminum finned baseboard and set-back thermostats set at 58 degrees night and 68 degrees daytime, while maintaining house temperature even on the coldest days.

It does take longer to heat up the house now but the temp no longer swings up past the thermostat setting and rooms that ran colder than others before now seem to benefit from the lower boiler temperature and longer circulator run times. If your guest-house is well insulated you can probably get by with these settings. If not, you can always bump up the high temp.

The lower aquastat settings should save oil due to reduced heats loss out the flue and from the boiler casing and also from the higher heat transfer efficiency from the burner flame to the colder boiler water.

The baseboard will now transfer less heat per hour per square foot at the lower temperature but the heat transfer efficiency will still be 100 percent.

Efficiency will not change with water temperature, only the heat transfer rate. Unintended consequences -

1) The basement is now cooler in the summer and more humid. Running a dehumidifier may kill my savings.

2) The internal cast iron boiler sections may be more rapidly corroding due to not being heated. (Feb 28, 2012)

Efficiency is actually "output divided by input".

Paul said:

Nick, I have a Weil-Mclain Gold Oil Burner Model P-WTG04 series 3 boiler. I have 4 heats zones controlled by an Agro controller. I also have an Amtrol Boiler mate for hot water connected to the Argo priority zone.

What should I set the Honeywell 8124 A aquastat. I am confused as the what differential and Low limit should be used, It is presently set 160 H 140 Low and 15% DIF. Thank you for your help!

(mod) said:

Nick, for reasons we explain in AQUASTAT HI LO DIFF SETTINGS, we don't prefer your aquastat settings for a boiler that includes a tankless coil.

Buddy, thanks for the helpful detail and update.

On most points including your advice to Radhames, we agree completely. Contact me by email if you want to be more fully identified as a reviewer/commentator. (June 14, 2012)