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Community and Q&A

What to do about basement / lower level temperature after switching from boiler to heat pump?

mpchadwick | Posted in General Questions on
In the fall of 2020 (about 1 year ago) we had a Mitsubishi Hyper Heat heat pump system installed in our house with the idea being for it to replace our old boiler. One thing we knew would be an issue going into it was that there would no longer be any heat source providing heat in the lower level of our house.
We have three rooms in the lower level of our house
– The “basement” room – In here we have our washer / dryer, a chest freezer, and we also use it as a pantry for food. There are water pipes in here (~162 sq ft)
– The garage – Just a storage area. There are water pipes in here.
– The boiler room – Our old boiler and oil tank are in this room. Also has our hot water heater. There are water pipes in here.
 (~183 sq ft)
Given that all the rooms have water pipes and some of them have other appliances that hold water freezing is a definite concern, so prior to last winter I put a bluetooth thermometer in each room and monitored the temperature throughout the winter. When it read below ~40 degrees Farenheit (which it did multiple times throughout the winter) I turned off the heat pump and turned the boiler on. This significantly raised the temperature on the lower level and prevented any freezing in the lower level.
However, long term we would like to get rid of the boiler entirely, but we need a solution to prevent any damage that could be caused by freezing temperatures in the lower level.
My current thinking is:
– Garage: We will use heat tape (this one just to keep the pipes from freezing. The water pipes are the only thing I’m worried about here, so I don’t think we need to heat the entire space, just keep the pipes from freezing
– Basement / Boiler Room: Given that these rooms have appliances that contain water (the washer in the basement, the water heater, and currently the boiler, although long term we’d like to have that removed, in the boiler room) my current thinking is that I need to keep the air temperature in these rooms above freezing, not just the water pipes. I’m currently still very unsure on what the best way to do this is. The prospect of using space heaters for this seems worrying to me due to the fire risk as they’d be running unattended for multiple days, so I’m thinking maybe I could use electric baseboards. I’m thinking they could be plugged in through a “Thermo-Cube” so that they only turn on when the temperature is at risk of going below 32F. Even still, given that the boiler room has an oil tank in it I’m not sure if there’s really any safe way to do this?
I appreciate any and all advise on this matter.

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  1. walta100 | | #1

    Wild guess is that you have lots of air leaking out of your upstairs ceiling into the attic and out of the house that air must be replaced and that air tends leak out at the highest point and be replace at the lowest point so you have a cold basement.

    Start with a blower test calking the leaks at the highest and lowest points first. Put a box fan in a window and use incense sticks for smoke and find the leaks then caulk them. Note turn off the water heater and boiler as the fan may make them back draft.

    It seems likely you have little or no insulation on your basement walls.


  2. Jon_R | | #2

    > Basement / Boiler Room

    While moving 70F air around to maintain 70F somewhere else isn't feasible, maintaining 40F is. So if you need more heat after air sealing and insulation, look into moving air from the heat pump heated area.

  3. CollieGuy | | #3

    After you address any insulation and air leakage issues, you might consider a low wattage oil-filled radiator. I have one in my home office that draws just 300-watts, and the surface never gets overly hot. Conventional electric baseboards scare the hell out of me as anything that comes into direct contact could pose a potential fire hazard.

  4. Expert Member
    NICK KEENAN | | #4

    If you goal is just to keep pipes from freezing, almost everywhere in the US you can accomplish that in a basement with insulation alone.

    Find out what your local frost depth is -- how deep pipes have to be buried to keep them from freezing. A rule of thumb is that dirt has an R-value of about R4 per foot. So that gives you an idea of what kind of r-value you need between the outside and an unheated basement with an uninsulated floor to keep pipes from freezing.

    That doesn't solve the problem of the floors in the conditioned part of the house being cold. To solve that you need to either make the basement part of the conditioned part of the house, or insulate between the basement and the conditioned part of the house. I would recommend the former.

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