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To freeze or not to freeze

Wade Rikert | Posted in Energy Efficiency and Durability on

I have a current client who wants to turn heat off to there summer lake house every year from November to April. The house is in the process of being built right now. It is a high efficiently Vermont certified house when completed. My question is whether the little bit of saved propane fuel is worth freezing the house or not? What long term impacts can happen with these types of homes with this much insulation and air tightness? My fear is that solar gain into the house could create dew moisture, and also further push the dew point into the interior leading to drywall mold over the next few years. It has 2 inches of continuous foam on the outside with r-40 walls and r-60 attic… with blown in for both. Are these homes resilient enough for this?  Thanks you in advance for your thoughts.

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Replies

  1. Jon R | | #1

    Solar gain wouldn't cause a moisture issue. I'd think about getting all water out of pipes (PEX pipe + compressed air works well for me) and foundation damage (many depend on interior heat to prevent freezing). Heating systems can fail - so these concerns exist even with planned heating.

    IMO, a dehumidifier is always a good idea for sealed, otherwise unconditioned buildings.

  2. Expert Member
    Zephyr7 | | #2

    Water in the pipes is probably the biggest issue. It can be difficult to get all the water out of all the places it can cause problems. A little water left in a horizontal pipe usually isn’t a big deal, but a little water left in a shower valve can destroy the valve (I’ve seen this happen). You then get to discover all the exciting leak locations when you pressurize the system in the spring, and these leaks always seem to be in difficult to access locations. Small leaks inside walls can cause a lot of damage before they’re detected too.

    If you are serious about winterization, pitch all the water SUPPLY lines towards a low spot you can drain. Plan to blow the system out with compressed air like the sprinkler crews do when winterizing systems. Don’t forget to put RV antifreeze in traps.

    Wood trim can sometimes have issues with big thermal changes too, but I’d be more concerned about water lines. Another thing to be careful of is to be sure to fill your water heater before turning it back on. I’ve seen people turn things on in the wrong order, or forget to open the right valve, and burn out a water heater that has no water in it.

    Bill

  3. Expert Member
    Malcolm Taylor | | #3

    Wade,

    In my experience it is more the contents than the structure that benefit from a level of heat throughout the year. People fortunate enough to have had summer cottages will remember the slight mildew smells that mattresses, linens and books take on. The veneer of rust baseboard heaters, wood stoves and hardware get. In most climates it is all fairly cosmetic. Whether not is worth maintaining a minimum temperature is probably a call that can be reasonably made either way.

  4. Stephen Sheehy | | #4

    What are they using propane for heat in a new, well insulated ( and presumably air sealed) house? Propane heat will be at least twice as expensive as a minisplit. If it isn't too late, I'd install a single minisplit, leave interior doors open, drain the pipes just in case, and leave the heat at 50°. If there is any solar gain through windows, the house won't need much heat at all to stay at 50°.

    1. Wade Rikert | | #6

      Hi Stephen. It’s currently not too late for a minisplit system. It’s open concept on main floor so atleast a one zone could work nicely. I chose a combi boiler for space savings as I also need to have an erv system installed per requirements of Efficiency Vermont. The minisplit would be outside I realize. That said my though was to just keep to two systems and not add a third. An on demand combi boiler is only $3500 which comes with on demand hot water and takes up very little space. How much does a one zone minisplit tend to cost? I realize installation is not included.

      I already knew about draining pipes and antifreeze. That’s all common sense. It’s more what impact does it have on the drywall over the years. Also any bit of moist smell as described by another responded means not good. Keeping window shades open I like as the solar gain can help. But I also want to avoid freeze thaw on interior of the windows. So not sure what the impact is for that.

      1. Stephen Sheehy | | #7

        A Fujitsu or Mitsubishi cold climate minisplit should cost about $3500 or so installed. Just mount the outdoor unit where it won't get buried by snow.

        For a summer hou erv, how about a pair of Lunos? Most of the time, ventilation won't be needed since the windows will be open in nice weather.
        The minisplit has the added benefit of air conditioning for the occasional hot day.
        Both take up way less room than any boiler. And with a boiler, you either need to fill with antifreeze or drain it.
        As I mentioned, propane is much more expensive to heat with than a minisplit or anything else.

  5. Tom May | | #5

    As all the others have said, just make sure all water is drained from piping, faucets, valves and appliances. Zephyr7's second paragraph is right on. Even leaving a pilot light on will create excess moisture which will cause rusting of components, so be sure to turn off all the gas also. As Stephan said, solar gain in the winter is usually enough to keep the inside somewhat comfortable and dry so be sure to leave shades open to allow sunlight in. Most people tend to cover up windows to keep people from looking in, but if you are in a safe spot it's best to leave them open, even if it's just a second floor. Adding a small solar fan set up isn't a bad idea either to circulate and/ or remove stagnant winter air, especially if it is to be a 'tight" house. A solar hot water system could also be considered for summertime use and free winter heating using baseboards or old cast iron radiators.

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