Authors pickup truck in front of a winterized and frozen-in building in upstate New York (C) Daniel FriedmanWinterizing Guide, Heat Left On
How to Freeze-Protect Water Supply Piping, Drain Piping, Water Pumps, Tanks, Heaters - Leaving the Heat ON

  • WINTERIZE - HEAT ON PROCEDURE - CONTENTS: How to winterize or freezeproof a building - how to set the down thermostat but keep HEAT ON. Thermostat Settings Recommended to Avoid Freezing. Guide to Turning off Water to a Winterized Building. Winterize a Water Softener or other Water Treatment Equipment?
  • POST a QUESTION or READ FAQs about how to winterize a building when some heat is going to be kept on.

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How to freeze proof your building while keeping the heat on: this article explains in detail how to winterize or freeze proof a building when some heat is going to be left on in the structure.

We explain how to set the thermostat to a lower temperature to save on heating costs and how to figure out just how low you can set the thermostat without facing a freezing problem.

We discuss winterizing the water softener and other equipment. The articles at this website will answer most questions about freeze protection for piping and other building plumbing and heating system components: how to winterize a building to avoid frozen pipes, and how to thaw frozen water supply & drain piping, wells, & water tanks. Our page top photo shows an old octopus furnace in a building where heat is to be left on.

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How to Winterize a Building If you are Keeping Heat ON

Honeywell room thermostat

Is the building heat going to be left "on" or "off" - the answer determines the extent of freeze-proofing needed.

The simple steps to winterizing a building where heat is being left on include choosing a low setting for the heating thermostat, turning off all or portions of the water supply piping, locating and correcting points of extra risk of freezing, and possibly the installation of a freeze-alarm notification system.

Thermostat Settings Recommended to Avoid Freezing

How to find the lowest "safe" temperature for setting the thermostat. In theory we simply need to keep the building just above 32 degF. But actually dropping a building interior temperature down that low is risky.

Why? Because often there is some cold corner, under a sink cabinet, or in a drafty basement corner, where temperatures can fall far below the number set on the building thermostat.

So we need to keep the building temperature at the thermostat high enough that the coldest spot in the building where piping may be exposed to freezing will remain warm enough. Other building corners can get a bit colder if the do not contain anything in danger of freeze damage.

If the Freeze-Safe temperature is Unknown: set the thermostat at 56-58 degF: If you have no experience with how a particular building behaves in freezing weather, it's smart to start by keeping the temperatures pretty high. It's usually "safe" to drop a thermostat to 55 degF. or even down to 50 degF (though below we also offer a few simple extra things you can do to avoid freeze-ups).

But if the building is an older one with drafts and unknown freeze points, keeping the temperature a bit higher is a bit more safe. That's why some experts suggest the 56-58 deg.F. setting above.

Use remote sensing to monitor and if necessary adjust building heating thermostat temperature settings. A range of companies produce temperature monitoring systems that can turn on a light (to be seen by neighbors), notify someone by telephone, or even monitor building conditions by website data.

For example, Proliphix provides a range of energy control thermostats that offer remote temperature control via web-enabled communication between an individual and the building's HVAC controls.


Also see NEST CAM INSTALLATION & USE as well as NEST LEARNING THERMOSTATS for advice about how to use these smart devices to improve building freeze protection as well as to monitor a building for frozen pipes, water damage, or for building security.

How to Prevent Pipes from Freezing in a Heated Building

Air register added to stop freezing pipes (C) Daniel Friedman

Approaches to the freezing pipe problem in a building where heat is left on but pipes still freeze include:

A client had recurrent freeze-ups of his hot water heating baseboard piping (where the circulating water can be 180 degF !).We found a very cold drafty corner in a crawl space where freezing winter air was blowing right across an elbow in the hot water heating baseboard piping.

Empty house freeze protection (C) Daniel Friedman

When the building thermostat decided that the living space was warm enough and thus turned off the heating boiler and circulator, this cold corner would freeze in very cold windy weather.

The solution was simple: block the draft and insulate the corner. (Continuous operating hot water circulation as a freeze-protection method is discussed below).

Our photo (above left) shows how we stopped freezing pipes under the second floor of a home.We cut an opening into a pipe chase through which both supply and drain piping rose upwards to the floor above. Details about this approach are

Our photo at left illustrates another example of strategic placement of openings to permit some circulation of warm air into a cold space.

In choosing whether to rely on heat tapes (not much good if there is a power loss), providing an actual heat source, directing heated air into a cold space, adding insulation, or relocating pipes at risk of freezing we often have to balance home energy & heating costs against remodeling, renovation costs against in turn the probability of and cost of frozen pipe damage to the structure.

How to Find the Safe Set-back Temperature for a Heating Thermostat

It's easy to do a little experimenting to find out just how low you can safely set building temperature without freezing anything if the building is occupied or if the building can be checked regularly. To start we set the thermostat down to 56 deg. F, remembering that the thermostat is only monitoring the room temperature at the precise spot where it is located.

So other building locations may be warmer or colder. We watch what happens in areas of the building distant from the thermostat and possibly exposed to colder conditions.

We find the coldest point where plumbing or other freeze-protected components are located. That's the temperature that we monitor as we step the thermostat lower and lower.

40 deg .F. Using this approach it may be possible to drop a building interior temperature to 40 degF. without freeze damage occurring.

How to set a thermostat below it's official minimum temperature: if your building thermostat is an older model that does not permit temperatures to be set below 50 or 55 deg .f. it may be possible to "fool" the thermostat by tilting it out of level on the wall, so that a setting of "55 degF" on the thermostat dial is really equivalent to "45 degF".

A little experimenting (at a higher temperature) will show you how much to turn the thermostat on the wall to re-set its operating temperature range.

Why we like to keep some heat on: Even in a building with no plumbing to freeze up, it's usually better for the building to keep some heat going at this level than to allow it to reach zero or sub-zero temperatures. You may find that allowing a building to reach very cold temperatures can result in movement of building materials or cracking damage such as to flooring or even wall materials. In some locations there may also be a risk of elevated indoor humidity leading to mold contamination even if the building piping is not leaking.

Now that we've agreed to leave some heat on, it is still important to find freeze-risk points and to take some steps to avoid freeze damage by turning off water where we can, adding point heat sources, fixing drafts, etc. An experienced home inspector and some heating contractors or insulation contractors can probably point out spots where there is an extra risk of freezing pipes.

Guide to Turning off Water to a Winterized Building

Schematic of a main water shutoff system (C) Carson Dunlop Associates

Just below we will summarize the questions and answers about whether or not it is ok to turn off the building water supply when leaving a winterized building with heat on.

Turning off the water supply to a winterized building is the single most significant step that can be taken to protect the building from water damage due to frozen pipes.

If the building main water valve has been closed (shut-off), even if a pipe should freeze and burst, the volume of water that spills into the building will be minimal in comparison with the terrible flooding that occurs if a pipe bursts, the water supply has been left "on" and no one is attending the building.

Sketch at above left was provided by Carson Dunlop Associates and is used with permission. You can see the main water shutoff valve just above the building floor where the water pipe enters the building.

When is it Ok to turn off the water for a Heat-On Winterizing Set-up

If the building is heated by a warm air furnace or by electric heat, that is, by a heating system that does not require water (such as a hydronic boiler or a steam boiler), you can usually turn off the building water supply with no problem.

When is it NOT Ok to turn off the water in a Heat-On Winterizing Set-up

But if the building is heated by a system that requires water, such as a steam boiler or a hot water (hydronic) heating boiler, turning off the building water supply can risk serious damage or total destruction to the heating boiler or even unsafe conditions.

That's because most heating systems that use water rely on the presence of an automatic water feed valve to assure that makeup water is sent into the heating boiler whenever its water level drops below a safe level.

Detailed step by step instructions for deciding to turn off water and when where and how to turn off building water supply can be read


and LOW WATER CUTOFF CONTROLS for more discussion of heating boiler water control valves.

Details on how to find and use water shutoff valves is

What about leaving water running slowly to avoid frozen pipes

This is a last resort measure which we don't like. Not only are we wasting water, we risk flooding a septic system, or we risk freezing the building drain lines by the slow flow of water.

In emergency however, such as loss of heat during a winter storm, this step could be necessary and would make good sense and I would consider leaving a trickle of both cold hot water on if it meant avoiding a more costly freeze-damage problem. I'd want to run water fast enough that I guess it's not freezing in a shallow or exposed drain or sewer line.

Watch out: while some experts advise leaving faucets open or dripping to avoid freezing pipes, this advice is risky if the building drains are exposed to freezing. In many areas the building main drain exits above the frost line and can be exposed to very cold conditions. During normal plumbing use the surge of wastewater down the drain makes it past this cold spot without freezing.

A trickle of water can be cooled enough to freeze in the bottom of cold sections of drain piping; ice will build until eventually the drain is blocked (which can cause a sewer backup in occupied buildings). Eventually enough ice pressure may form to break the drain line.

Fine Tuning Building Winterizing Procedures: Temperature Setting Choice, Plaster Damage, Water Softeners

Do I need to to Winterize a Water Softener or other Water Treatment Equipment?

Photo of a home water softener system (C) Daniel Friedman

Even if you are leaving heat turned on in an unoccupied building during winter, it still makes sense to turn off the water softener .

If heat is going to be turned off in the building the water softener and similar water treatment equipment needs to be winterized.

See WATER SOFTENER / TREATMENT TURN OFFfor the water softener winterizing procedure.

When the building is reoccupied, you'll need to take these steps to get your water softener working again. Those steps are detailed

Question: I kept the house temperature at 50 but pipes froze and there was expensive damage

I am renting a historic house in Middletown CT which incurred some damage when the freezing weather came through Jan 24th. Two bathrooms located on the outside walls had radiators that burst and one toilet tank exploded. When the ice thawed the water ran on the kitchen floor and caused the floating floor to buckle

The owner has given me a bill for $15,000 because I keep the temp at 50. Would this temperature be the total cause of this damage or could his poorly insulated house be blamed? The house was built in 1800s and is 3500 sq feet. Looking forward to your response. Thank you, - P.M. 2/20/13

Reply: why a house with the thermostat set at 50 can still freeze-up

Pipes in a cold wall of a poorly insulated house might freeze even though the temperature inside the occupied space is warmer. Therefore if the bathrooms where the freeze damage occurred had actually been at 50 degF, the toilet and radiator would not have frozen, much lest burst.

Watch out: Pipes in a cold wall of a poorly insulated house might freeze even though the temperature inside the occupied space is warmer. On older buildings, even with heat kept higher than 50F, I've encountered heating system freeze-ups in very cold weather. And if the building heat is supplied by hot water and the heating pipes themselves freeze, then the resulting loss of heat is sure to lead to trouble.

In other words even with the thermostat set at 50F the heating system pipes or plumbing pipes can still freeze where pipes are routed through cold locations. This is especially true if the heating distribution piping had the bad luck to be routed across a sill or other area where it was subject to cold air leaks.

A single small segment of frozen distribution piping is quite enough to shut down an entire heating zone, thus allowing other plumbing fixtures, radiators, etc. to freeze and break.

So how high did the heat need to be to prevent freezing?

The answer is ... I don't know. Even with heat set to 68 degF. heat distribution or plumbing pipes can freeze in very cold conditions if piping is routed through an exposed or drafty area. That worry is why in the article above we recommend that building owners or occupants try lowering temperatures gradually, inspecting for cold spots and watching for trouble in order to discover just how low the thermostat can be safely set for a particular home.

Often rental contracts specify that the tenant has to keep heat high enough to avoid freeze damage (that's a question for your attorney). If a home is poorly insulated and depending on the routing and location of piping, the net effect would be that the occupants have to keep heat at a significantly higher temperature.

If I were the landlord and knew the history of the home I'd most likely have given you a minimum heat setting that I considered safe.

But regrettably, I can't say exactly what would have been needed at a home I don't know.

What should the landlord have done to prevent pipes from freezing

I can't agree that the responsibility for this winterizing or freezeproofing failure is entirely yours.

If I were the landlord owning such a building and knew of the risk, I'd would have

Reader follow-up:

After reading your information I realize why the owners have a puffy, padded toilet seat in the bathroom that incurred the most damage, because it is a "high risk, trouble area." ... as it was so cold and taking a shower in that bathroom brought out goose bumps even in November.

Reply: adding heat at key points to eliminate freeze-hazards

Air register prevents frozen pipes (C) Daniel Friedman

Key in your story is that the freezing in the toilet - that would not happen without first having no heat in the bathroom: a condition that would more generally occur if the heating pipes froze first (the landlord's responsibility) not because you turned the heat down.

In a house I rented to others I knew where there were freeze risks: having owned the house for many years I knew exactly where the problems would be. So before renting I took these additional steps to freezeproof the house:

If your bathroom has no heat source of its own, the landlord ought to install one

. If it's not convenient to install a radiator or baseboard, a small wall-mounted electric heater is easy to add.

Question: will our plaster walls blister, crumble, disintegrate if we let our 1930's house freeze solid?

I have a house with plaster interior walls built in 1930. I was told to not let those walls freeze solid due to the moisture content in those plaster walls. If the temperature drops well below freezing, for a prolonged period, the moisture in the plaster walls will crystallize and cause the walls to crack, blister or crumble. Does this sound correct? - Michael Golden 2/28/2013

Reply: freezing temperatures alone won't crumble and blister plaster unless there were abnormal conditions of leaks and moisture


Unlike summer cabins and some vacation homes, most ordinary homes, including those built in 1930, were intended to be left with no heat whatsoever in cold weather. But certainly there are many homes still with no central heating, relying on perhaps a woodstove or two, that survive cold weather rather well.

In a home that does not have some unusual moisture level in its walls - say from leaks or condensation (those problems are themselves due to construction or maintenance problems) the moisture level of plaster will typically be below 12% and will not cause the plaster to crumble and fall from the wall.

However in both plaster wall and drywall finished homes exposed to very cold weather we do sometimes see a crack or two develop in walls or ceilings when temperatures range extremely.

In sum I would not expect actual plaster crumbling or blistering and I would not expect extensive cracking all over the place in a normally dry home exposed to freezing, but I might expect to see a crack or two attributable to thermal contraction. Usually in a home as old as the one you describe, it will have already experienced a time or two of freezing and such damage will already have occurred, leaving clues of its passage.

At HUMIDITY CONTROL & TARGETS INDOORS we discuss both the desired indoor humidity level and the means of measuring actual humidity. If you measure humidity in your home's walls at levels over 12 % I'd look carefully for the reason, and if you see wall moisture levels (using a moisture meter) over 18% you are inviting both insect damage and freeze damage.

Watch out: even if the plaster walls are not themselves the greatest risk of solid freeze damage in your home, it's unlikely that a 1930's home was built with piping designed to be fully drained to prevent freeze damage. You should take a look at our freezeproofing advice for buildings to be left empty with no heat on - found

Building Freeze Protection Articles


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