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Minimum Winter Home Heating Temp When Unoccupied

  • 1.  Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-16-2022 22:31
    I'm having a most interesting conversation about what the best strategy is for leaving a home unoccupied in cold Winter temperatures, in this case two months. Outside temps can get as low as zero, which means that with no inside heat the temperature can drop that much as well. I'm suggesting that to leave a home unoccupied it's best to turn off the water main to the house, open up all the water valves, starting with the lowest point and allow as much water to drain out as possible. 

    Standing water in plumbing fixtures, even in small amounts, can expand and cause breaking (including brass valves), so to be on the safe side I suggest keeping the heat on at 35 degrees min. I've never had a problem doing this...no freezing plumbing, no damage to anything indoors. 

    But a colleague of mine insists on leaving the water on under pressure, setting the hot water heater on vacation mode, and keeping the indoor temp set at 55 degrees. They think that with the water under pressure and a neighbor coming over once a week or in extreme temperature drops and running the water that the combination of 55 degrees and occasional running water that it's the best projection...against freezing, and their belief that furniture, books, jars of grains in the pantry, etc., all do better. 

    The latter seems like a big waste of energy to me, and if the power goes out and the temperatures drop then like they had in Texas last year you have a plumbing nightmare waiting to happen. 

    Thoughts? Are there any recommended "best practices?" You can read plenty about the 55 degree minimum set point online, but I'm not seeing much substance to them other that it's just "a good idea." 

    What would you do if it's your house?

    Dan

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    Dan Antonioli
    Owner
    Going Green
    ITHACA NY
    510-499-2342
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  • 2.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-17-2022 06:10
    Dan
    We have multiple customers that leave for the winter here in Syracuse. Most if not all go the 55 degree route. If it were me and I hope it is some day I would still drain the waterlines and shut the main off just in case something happens with the plumbing (seal goes bad on a toilet or valve starts leaking). I can't see it being good for all the contents of a home to be that cold during the winter months. last year we had 20+ days in a row of negative temperatures and were 30 miles north of Ithaca.  If your going to take the route of shutting everything down I would winterize the home just like you would if it was vacant. Completely drain the water lines using pressurized air and use antifreeze in the drain traps.

    Just My 2 cents

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    Donald Shetler
    Owner
    Energy Savers
    East Syracuse NY
    315-4373008
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  • 3.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-17-2022 07:11
    We don't have the option of blowing out the plumbing with compressed air, which is something I always did with my rural property, so I'm suggesting that we shut the main off, open all valves, and drain as much as you can. To prevent standing water from freezing and doing damage, I'm suggesting that the heater be set to 35 degrees, which of course is will above freezing. 

    So I see three issues here. One is why the magic heating number is 55 degrees. Why is that temperature so special and common? Even some old school thermostats are set to only allow for a 50 degree low point with no actual "off" position.  

    The second related issue is with freezing pipes. What temperature do people think a building needs to maintain to prevent water from freezing when it's unoccupied? 55 degrees? Why not 35 degrees?

    Third, why should the contents of a home be maintained at 55 degrees? Does this benefit the furniture, books, clocks? 55 degrees, really? A cold Spring day drops down to 40 degrees and you're going to keep the heat on at home to a min of 55 degrees? That seems highly wasteful to me, and globally I wonder just how energy is used to maintain this most interesting minimum temperature. 

    Dan

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    Dan Antonioli
    Owner
    Going Green
    ITHACA NY
    510-499-2342
    ------------------------------



  • 4.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-17-2022 11:20
    Why 50F or 55F and not 35F? That's easy. That age-old rule-of-thumb simply allows for the fact that plumbing is typically not fully contained within conditioned space. To what degree plumbing is warmed (or not) by interior air becomes a judgement call depending on routing and pipe insulation. Hose bibs are obviously at greatest risk, especially when the associated feeder lines are routed through exterior wall cavities, or through unheated spaces such as garages or crawl spaces. But in cold climates, hose bibs can freeze even if when the interior is warm, so I'm guessing that problem is already mitigated in one way or another given your location. 

    If it were my house, I would drain the plumbing supply lines and turn the heat off during a 2-month vacancy. But I don't believe all the water needs to be removed. Freezing water breaks pipes because it expands under pressure. Relieve the pressure and I don't see how the remaining water that freezes can break anything. But this is just me applying physics and logic. Admittedly, I haven't lived in a cold climate, but I do have some experience to back this up...

    My family has a lake house near Charlotte NC. When I was growing up, we drained the pipes every winter (the original cabin, built in the 50's, wasn't insulated or heated). Even though single-digit lows weren't uncommon in that area, we never worried about water in the drain traps or supply line sections that didn't gravity drain. Nothing ever broke when that water inevitably froze. I now live in the high desert in southeast Arizona where overnight lows are typically above the mid-20's. Our well head had exposed PVC supply pipes during our first winter. Those pipes froze several times that winter, but nothing ever broke (I've since installed insulation). That's because the volume of water in the plumbing lines is so large that the additional pressure caused by frozen water expansion in such a small section of pipe wasn't nearly enough to bust the pipe.

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    David Butler
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  • 5.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-17-2022 17:59
    David, 
    Standing water in otherwise drained pipes can cause breakage. Believe me, I've had to learn this lesson more than once. My rural property had a lot of seasonal outdoor plumbing..outdoor kitchen, solar shower, hose lines, etc., and the first year I shut the water off and opened all the drains I thought I had properly prepped the plumbing for winter. Come Spring, I was surprised to find several breaks here and there, some of the expensive and time consuming to fix. The only thing that worked was to blow out all the lines thoroughly.

    I can appreciate the application of "physics and logic" but I see no magic number with 55 degree temps in a house where the assumption is that this will prevent pipes from freezing. The warmer the building the less likelihood of freezing, but this is an energy smart group in here and I question the "wisdom" that you need to keep an empty building heated to 55 degrees when unoccupied, for plumbing or anything else for that matter. 

    As for hose bibs, there are some nifty units now that you can turn off inside the building thus allowing for the outside bib to be opened. These are horizontal units, not the vertical ones that will drain down below the frost line.

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    Dan Antonioli
    Owner
    Going Green
    ITHACA NY
    510-499-2342
    ------------------------------



  • 6.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-17-2022 17:03
    Hi Dan
    I just wanted to go down a little side road here. In our area, we have a lot of heat pumps. I have been told that heat pumps won't function at return air temps lower than about 55 degrees. Taking that into account, I tell them not to set the stat lower than 55 degrees and to turn most everything else off - including the hot water heater if it is within the structure. Alternately, to switch the heat pump to emergency heat and run the stat down as low as possible - hopefully to 45 or lower degrees.

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    Eric Miller
    Energy Services
    Benton REA
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  • 7.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-17-2022 18:29
    Eric, curious what type of heat pump you're using. Are they "cold temp" units? I'm new to the world of heat pumps now coming up to speed with them, so this is a most troubling reference.

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    Dan Antonioli
    Owner
    Going Green
    ITHACA NY
    510-499-2342
    ------------------------------



  • 8.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-18-2022 00:59
    Dan, I'm in no position to question your experience with broken pipes resulting from incomplete wintertime draining, but I can't help from wondering about the mechanism at play that would cause that. In any case, you may have a problem finding a thermostat that can be set to 35F. Also, if any of your plumbing is not fully within conditioned space, it could still be at freeze risk if you allow the house to get that close to freezing. And depending on how tight the house is and how well the rim bands are insulated, interstitial spaces that are ostensibly within the thermal envelope can easily vary several degrees from the temperature at the t'stat.

    Regarding Eric's comment... I was only addressing the pipe freeze issue and was imagining, perhaps incorrectly, that you would reoccupy the home in warmer weather (i.e., at least 2 months from now). But without further qualification, my advice was at best incomplete, as there are indeed concerns about heating a building that cold, depending on the type of heating system. 

    In the case of a heat pump, the main concern is that the defrost system won't work properly if the return air is too cold. Trane, for example, recommends a minimum return temperature of 55F for heat pumps in order to ensure proper defrost operation. You can avoid that problem by warming the building when outside temp is at least several degrees above freezing. Otherwise, you'd need to use supplemental heat only (EM heat mode), as Eric suggests. The other issue with heat pumps is recovery speed... the colder it is outside and the bigger the indoor lift, the longer it will take to recover from a deep setback.

    In the case of fossil fuel furnaces, an ANSI standard was modified in recent years specifically to address problems resulting from operating a furnace during construction (mostly related to contamination). One of the requirements within that section stipulates that a minimum return air temperature of 55F be maintained. The concern is excess condensation in the secondary heat heat exchanger, which could lead to corrosion. As a result, furnace manufacturers generally set a minimum return air temperature of 55F or even 60F.

    Although this new ANSI requirement specifically addresses operation during construction, AHRI commissioned a research study to determine if deep setbacks in vacation homes are detrimental to furnaces. The report concludes that non-condensing furnaces could indeed be damaged by operating with a low return air temperature (the units were tested at 45F), but that condensing furnaces were not affected. No surprise there. Here's a link to the study: https://www.ahrinet.org/App_Content/ahri/files/RESEARCH/Technical%20Results/AHRI_8014_Final_Report.pdf


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    David Butler
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  • 9.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-18-2022 06:33
    As interested as I am in heat pumps this topic is about plumbing and I'd like to stick to that. 

    Plumbing is rarely fully contained within conditioned space, at least for most residential buildings. There are always weak links and if the theory of applied heat is to have enough heating going inside a building to conduct freeze-protecting heat to the pipes then I would say this is a huge waste of energy, and BPA is very much about using energy wisely. Globally, I wonder just how much energy is lost and spent just to keep the lights on when nobody needs them on!

    And of course you have to wonder what happens when the power goes out, as it did in Texas last year and so many pipes froze and broke...after the power was restored, plumbing leaks wreaked havoc. So no amount of heat on plumbing will guarantee freeze protection. Turning off the main and draining the pipes is your best protection. 

    Thermostats come in many forms and finding one that allows for low set points, or off, is standard, even for many old school analog thermostats. The one in question here is somewhat unique in that it only goes down to 50 degrees and has no off position. Yesterday here in Ithaca, New York the outdoor temps got up to be 47 degrees. Snow was melting all over the place, rivers and gorges swelled, and there was simply no need to keep the inside temperature of an unoccupied building set to 55 degrees! A homeowner should simply be able to leave their house in the morning knowing that their house is just fine without the heating running for much of the day. 

    The larger picture here is to address all of the pieces of the energy efficiency puzzle and this is one big piece that rarely gets addressed.

    ------------------------------
    Dan Antonioli
    Owner
    Going Green
    ITHACA NY
    510-499-2342
    ------------------------------



  • 10.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-18-2022 12:30
    Dan wrote: "no amount of heat on plumbing will guarantee freeze protection. Turning off the main and draining the pipes is your best protection. ​"

    Of course. My point was simply that maintaining 35F won't necessarily prevent residual water in the pipes from freezing since sections of plumbing could be exposed to lower temperatures. And you can't advocate for such a low setting (or even more so, turning off heat) in a vacuum without considering the implications of re-heating from a cold start on heating equipment.

    "A homeowner should simply be able to leave their house in the morning knowing that their house is just fine without the heating running for much of the day."

    Deep setback for a single day or even a weekend, is a different discussion not likely to involve plumbing protection. In particular, heat pumps with electric supplemental heat could end up expending more energy to recover than was saved. 



    ------------------------------
    David Butler
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  • 11.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-18-2022 13:31
    David, 

    For purposes of this topic let's bracket off heating systems and take that up on another thread. It's relevant but not the topic

    I can make a case for 35 degrees because it's above freezing and if you've drained the plumbing and have residual water here and there then you're just doing your best with the least amount of energy to prevent breakage. Perfect system? No. But for that matter depending on the plumbing you could set the heating temp to 80 degrees and still have freezing. Even keeping the water running on cold nights can freeze unless the water is running at high enough volume. 

    Dan

    ------------------------------
    Dan Antonioli
    Owner
    Going Green
    ITHACA NY
    510-499-2342
    ------------------------------



  • 12.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-18-2022 15:28
    Assuming draining all of the pipes eliminates the danger of freezing pipes, the only real benefit I can see to keeping the thermostat at 55 is that it can prevent some level of shrinkage of building materials. Whats the difference between 55 and 35? I have no idea, but that's the only thing that I can think of. Could plaster crack or paint crack, could wood floors shrink to the point where cracks nails loosen and the flooring gets damaged/ What about adhesives for countertop or flooring? I certainly have more questions than answers but hopefully this helps move the conversation forward.

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    Mark J
    Advocap
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  • 13.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-19-2022 08:30
    One consideration that has not yet been discussed is the advantage of earth coupling for seasonal dwellings. Both experience and modeling have shown that a super-insulated building shell going down below the frost line, but leaving the basement floor essentially uninsulated can be a wise strategy for seasonal freeze protection with no additional heat in most climates. Unfortunately, many prescriptive building codes (including here in Vermont where I have a seasonally occupied house) are now requiring full under-slab insulation thus decoupling the house from the thermal storage reserve of the earth (that we so readily are wont to harvest with so-called ground-source heat pumps).

    No matter how well insulated a styrofoam box you build, without any source of heat, the interior will eventually gravitate to the outdoor temperature. Of course, we have also have not considered any of the advantages of sound passive solar as understood in the 70s (not necessarily today's "Passive house design" which are often anything but passive. 

    Combining true passive solar design with ground coupling is probably your best guarantee against winter freeze-ups in unoccupied buildings. Earth coupling can also have advantages in Summer months.  Of course there may some additional energy usage in the off seasons compared to state-of-the-art super insulated mechanically-driven systems, but these can be both complex and prone to failure.

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    Tom Wilson
    HOME REMEDIES Residential Energy Services
    Viroqua WI
    715-829-3512
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  • 14.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-19-2022 09:23

    I had experience with exactly what Tom is describing.  During the ice storm of 1998 I had left my house in Maine to return to PA the day before and had done all the normal setbacks that I would do including setting the thermostats to 55.  Then the next day the storm hit and then subsequently the power was out for close to a week.  I had a caretaker who kept checking the house and just to check he things completely he left a thermometer on the basement floor.  It never went below 35 or 40, I cannot remember the numbers but it did not freeze.  The house was tight for its day (2.4 ACH@50) and well insulated so no damage was done.  

    That house had a hydronic heating system so turning off the main water supply would mean no make-up water for the boiler.  So I always left it on and had no trouble.  I would turn off the boiler mate water heater but otherwise always left the plumbing on.  I never had a broken pipe.



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    Kent Kjellgren
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  • 15.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-19-2022 09:51
    Kent,
    What you describe is identical to our situation in our house in Warren, Vermont.  It's a 1970s timber frame that has required extensive deep building shell retrofit but built on ledge with excellent earth coupling; Same strategy with the boiler and the water heater side arm.

    My house in Wisconsin is a high-mass double-wyth brick Victorian with a deep foundation, all plumbing isolated from exterior walls and excellent solar gain from the original south-facing windows.

    In both cases as we go back and forth between the two, I turn the thermostats down as low as possible...usually about 40° or 45°F.

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    Tom Wilson
    HOME REMEDIES Residential Energy Services
    Viroqua WI
    715-829-3512
    ------------------------------



  • 16.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-19-2022 11:13
    Hi Tom, I've been advocating for ground coupled slabs for 15 years (passive solar for even longer) so I'm happy to have some company! The key of course is a well-insulated perimeter. But there's a caveat that can't be ignored... A Canadian study has shown that sub-slab moisture can collapse the thermal zone that forms beneath the slab by transporting heat away from the foundation. So ground coupling works best when sub-slab soils are mostly void of moisture. In hot climates, that's not an issue.

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    David Butler
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  • 17.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-19-2022 11:43
    David
    Normally the recommendation is to insulate the perimeter of the floor, like 4 ft in and just leave the center uninsulated. Your point is well taken and as I tried to imply in my original comment, there may be an energy penalty for a house that is heated all year round, but if you can totally shut off your furnace for significant periods of time when no one is there, that more than makes up for the for the losses when heated.

    In an unheated house, I would not characterize it as "...transporting heat away from the foundation," but rather transporting heat from earth's thermal zone into the basement.

    That's one of the key issues I have with most modeling programs...and the codes that they produce...is that they assume the house is heated to 70° 24/7 irrespective of how the house is actually operated.

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    Tom Wilson
    HOME REMEDIES Residential Energy Services
    Viroqua WI
    715-829-3512
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  • 18.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 02-22-2022 16:09
    Winterizing a vacant house is like winterizing our stored RV. Drain the water lines, blow out the water traps or pour RV Antifreeze in them. Many fill their water lines with RV Antifreeze to protect the lines and valves from freezing of any remaining water, though I would not recommend filling a residence plumbing system. Perhaps a little in the traps.

    I have worked on low income housing were we had thermostats set to 65F and water lines freeze in basement crawl spaces due to wind chill on uninsulated water pipes. Solved the wind chill issue by sealing the leaky return ducts in the basement!

    One issue not mentioned in the discussion is indoor humidity. As the temperature drops the RH goes up. For RVs that are stored without heat, owners often add devices to absorb interior moisture to reduce interior condensation. In residential dwellings there is possibly enough soft surfaces to absorb.

    Long term food storage should be reviewed for the type and its packaging. Air tight grain should store well, though other foods items may not.

    As mentioned, any advice needs to be tailored to the type of dwelling it is applied to. An air tight house performs differently than a leaky; well insulated performs better than less insulated; different types of heating system have their own issues, as mentioned. There is no one answer, though we all need to be aware of how the variants effect our recommendations.

    Great discussion.

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    David
    ConservFirst
    NM
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  • 19.  RE: Minimum Winter Home Heating Temp When Unoccupied

    Posted 05-03-2022 07:24
    Hi David. Can you say a bit more about the "RV Antifreeze?" I'm familiar with food grade antifreeze used for solar thermal systems, is this the same stuff?

    ------------------------------
    Dan Antonioli
    Owner
    Going Green
    ITHACA NY
    510-499-2342
    ------------------------------