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How can I evenly heat a house with a partial basement, as shown in the diagram below? The rooms over the slab are consistently several degrees cooler than the rooms over the basement, particularly when the doors are closed for a while.

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The portion of the house on the slab foundation is heated from ceiling vents whereas the portion of the house that is over the basement is heated from floor vents. The ceilings are 9 feet high, which may contribute to the inability of the heat from the ceiling vents to circulate throughout the rooms.

This is a new house with good insulation and windows. The portion of the house over the basement is mostly one open space, whereas the portion of the house on the slab is divided into two bedrooms and two bathrooms.

I have tried closing or mostly closing the vents in the portion of the house over the basement in an attempt to get more heat to the portion of the house over the slab. Leaving doors open helps the issue some, but it is not desirable to have to leave the doors open all the time.

Is the HVAC for this house set up appropriately? What measures would help heat the house evenly?

  • In the area of the house that's cold, do each of the rooms have both a register and a return? This is a forced air heating system, right? What is the outdoor temperature? Is the basement heated? Was the entire house built at the same time? Are there more windows in the cold area? – Tester101 Oct 26 '16 at 12:42
  • You need either to balance the airflow (and stop closing doors or install some air returns) or put in separate thermostats to control separate blowers. Do you even have blowers, or is this supposed to be a fully passive system? – Carl Witthoft Oct 26 '16 at 14:47
  • Could you amend your diagram to include the air returns? – Bryce May 16 '18 at 21:28
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Hot air rises, so the area with overhead vents are fighting convection. You might install a reversible ceiling fan, a small vent booster fan or an in-line duct fan, at the expense of a bit of electricity and perhaps noise.

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My house has the exact same issue. I have what is referred to in the midwest as a California room (no idea why). Room that is slab only with a huge amount of windows.

So the possible issues:

  • poor barrier on the slab. I noticed a change from going from carpet to best pad plus carpet - no more cold carpet. Which means the slab was cooling the room in the winter.
  • Often these types of rooms have more windows
  • which really comes down to these types of rooms aren't insulated as well - especially if built 20+ years ago.
  • your attic is way cooler than your basement in the winter
  • the runs through your attic out to this room are way longer

Solutions:

  • get an oversized furnace (I did this and it helped dramatically). Bigger furnace outputs heat faster so chances are this room will get hotter air. I noticed the outputted air in my California room as 8 degrees hotter when I upgraded. Not that an oversized furnace in this case is not performing worse, because you have a special case for one. If you got the right sized one, you would overuse it.
  • Run wider ducts to attic and to room.
  • Make sure these ducts are double taped and glued at seams.
  • I see better airflow with rigid ducts - much better.
  • Make sure your ducts are well well insulated in the attic.
  • Think about reinsulating the room or buying better windows for that room.
  • Buy an electric fireplace for that room.

Any or all of the solutions I gave you will work/help. I wouldn't upgrade to a bigger furnace unless my furnace was on its last leg. Wider ducts might be close to impossible or easy too (or maybe not doable until furnace upgrade). The first two things are sealing those ducts and insulating them because this is $50 at most and a long-term investment that will pay off. Reinsulating the room means taking down drywall probably unless you need new siding. So buying an electric fireplace might be one of the easiest things.

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