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Community and Q&A

How to condition a basement on new construction

bwcaw | Posted in Mechanicals on

I am building a new house and want to know the best way to keep the basement well conditioned. 

–Northern Michigan zone 6a
–1200 sq ft foot print (30×40), 2 story with 10′ basement, so 3600 sq ft total.
Basement will be finished. Bedroom, bathroom, storage/mechanical room, and open play area.
–45 ln ft of daylight wall with windows.
–Basement will have R16 continuous rigid insulation on walls, and R13 under slab.
–Heat will be natural gas furnace with whole house humidifier
–We want 1st and 2nd floors on their own zone (all bedrooms on 2nd floor)
–Current recommendation by HVAC contractor is to have basement on it’s own zone as well.

We want a well-conditioned basement with proper humidity levels. Our current house we experience too cold in summer and winter.

We’re just getting weathered in now and slab is not yet been poured. Is there a better/best way to condition the basement?

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  1. matthew25 | | #1

    Are you doing a traditional forced air heat pump for the rest of the house? Be sure to account for the load of the basement when sizing your heat pump. Or install a separate unit just for the basement.

    1. bwcaw | | #2

      House is spec'd for one forced air natural gas furnace.

  2. bwcaw | | #3

    I see mixed reviews online about a separate zone for basement. It's a $2000 extra cost. Wondering if that money is best saved and just tie basement to 1st floor zone or spend money for another system for basement like mini split or in-floor heat.

    1. paul_wiedefeld | | #4

      You’ll want it ducted. So heat pump, furnace or both, ductwork is key. Radiant is too expensive for you if you’re worried about $2k.

      1. bwcaw | | #6

        No so much worried about the $2k, rather wanting it to go towards the better option to maintain a comfortable finished basement. If ductwork is key than that's what I'll have after this zone install. If it doesn't work well I could always add another furnace or heat pump just for the basement and take over that ductwork.

        1. Expert Member
          DCcontrarian | | #7

          With 3600 square feet, even in zone 6 your heating load should be under 40,000 BTU/hr, one furnace should be fine and your challenge might be finding one that's not oversized.

  3. Expert Member
    DCcontrarian | | #5

    Re: the humidifier. The reason houses get dry in the winter is that the moisture content of outside air is very low, when it leaks in it is very dry. Occupant activity -- bathing, cooking, breathing, sweating -- puts about five pints of water a day per person into the air. If your house is well-sealed the humidity lost through air leakage is balanced by the moisture from occupant activity, you may even have to vent excess humidity. The number one thing you can do for comfort is make sure your house is well sealed. And if you're not measuring, you're just guessing. The way to measure air-tightness is through a blower door test. Code minimum is 3 ACH (air changes per hour), you should try to go lower, 1.0 is a reasonable goal in new construction.

    The number two thing, close behind, is make sure your house is well-insulated. The latest codes are pretty good, make sure even if you live in a place where codes aren't enforced that your contractor plans to insulate to current codes, and it's something to keep an eye on during construction, a lot of people -- even insulation installers! -- consider insulation to be nonsense and will cut corners in difficult to access spots, don't let them do that to you.

    It's much easier to make your house comfortable with sealing and insulation than to try and make up for the lack of it with a heating system.

    With modern levels of insulation and sealing the basement should be pretty comfortable. But the temperature down there depends on how much heat leaks out, and how much you put in. It's that simple, there's no magic. We've already talked about minimizing the heat leaking out, but you still need to put in enough heat to keep it at the temperature you want. If the basement is its own zone, the thermostat will keep it at the set point unless the system is mis-designed. If the basement is on the same zone as the rest of the house, the basement will get a fixed proportion of the heat needed to keep the rest of the house at a set temperature. So if it's a cold but sunny day the upstairs may be warming under the sun and not need much heat, but the basement doesn't see the sun and would be underheated. Similarly, if it's cold and windy the upstairs may need a lot of heat and the basement ends up overheated.

  4. amandawil | | #8

    Conditioning a basement in new construction is crucial for comfort and moisture control. Ensuring your house is well-sealed is key, and measuring air-tightness through a blower door test is essential for accuracy. Aim for lower air changes per hour for optimal results. For more detailed guidance, check out this website!

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