Should I install door to separate main floor from basement?
gi4ever
| Posted in Energy Efficiency and Durability on
Good morning everyone. Wondering if we should place door at bottom of stairway (top just wouldn’t work) of raised ranch home. House is new and we’re finishing our basement. Both floors will have conditioned space with supplies, returns, etc. Will this help the basement area maintain temp/humidity better? Or is this a fool’s errand? Thanks.
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G.I.,
When a multi-story house lacks enclosed stairways with doors, it can be hard to maintain even temperatures on each floor (especially with single-zone heating systems, and especially in homes with leaky thermal envelopes that encourage the stack effect).
For that reason, I'm in favor of basement doors.
Thanks Martin! Just for additional info's sake, I'm in the Midwest.
Heat source mixing plays a role. Proper distribution and register throw produce little stratification - ie, there just isn't much cool air to sink into the basement.
But doors have multiple benefits and can always be left open.
It has been my experience that a multilevel home with adequate levels of insulation and reasonably airtight 2ach50 or less will maintain uniform temperatures between floors with an open stairwell. Let me qualify this by saying the forced air heating was zoned for both levels and the basement floor had R-10 subslab insulation. For this project we had considered radiant tubing in the basement slab but the cost for another high efficiency appliance plus the tubing was just too high (about 12k). The cost to zone for the lower level was $2,500.00 with the forced air system. I sort of went out on a limb and recommended the zoned option with a promise of lower level comfort. The subslab rigid insulation is critical to minimizing temperature differences between levels. In a blindfold test you would not know which floor you are on in this house, the lower level is just as comfortable as the main level.
Our own house, built by others, has forced air heat on a main floor thermostat. The basement is heated but has no insulation under the concrete slab, the foundation walls are R-10 interior polyiso. There is a door to the basement level and the temperature in the winter is main level 70F, lower level 65F.
3-14-18 update for our Eden Prairie, MN house Main floor 72F Lower level 66F Slab temperature 62F Full sun today, balance point reached at 11: AM, 32F outdoor, furnace will take the afternoon off. :)
Excellent information. My own house does NOT have slab rigid foam (much to my dismay, I learned the benefits after it was built). In fact, my situation is as Doug's above. Single furnace, thermostat at upper level, single zone. I'm playing with the idea of multizone as I finish the space. In any case, better to have it and not need it right?
I'm also insulating according to Martin's guidance. Spray foam over concrete and blown fiberglass in 2X6 walls with Membrain barrier.
Jon R made a good point in the mixing of heated air and comfort. High supplies and low returns or vice versa in the lower level will promote good mixing. Generally not enough supplies or returns are put in the lower levels as in our case, 4 supplies in basement, 11 supplies on main level. Even though heat loss through insulated basement walls does not come close to the heat loss through all of the main floor building elements you still need an adequate number of basement supplies. Error on the side of too many and let the heat work it's way to the main level.
Excellent advice and common sense approach Doug. HVAC for downstairs is first week of May. I'll certainly talk with him about that.
One more update on basement floor slab temperature. 62F was the center of the slab, near the footing with full height basement wall, 57F, slab temp near basement walkout, 55F. I suppose if we kept a basement temperature closer to 70F these slab temps would be correspondingly higher. However, with the Earth connection to the basement slab in a cold climate, there will always be a temperature differential during the heating season. I offset this loss some in the cooling months with a large (dampered, closed in winter) return near the basement floor allowing the cold air near the floor to be mixed in before traveling over the cooling coil of the AC. With a couple of large deciduous trees shading the house in the summer months our cooling costs are very low if we use the AC at all.