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I have a finished basement with an open stair well to the 1st floor which even in the middle of the summer needs to be heated to stay at 69F degrees. There's also a large open foyer leading to the 2nd floor. I'm thinking of moving hot air on the 2nd floor down to the basement. Would this help?

Some house details:

  • Basement (1500 SQFT) is open to the 1st floor through stairwell
  • 1st floor (2000 SQFT) is open to the 2nd floor through foyer
  • 2nd floor (600 SQFT) has some common space and two bedrooms
  • Every room and a common space has individual returns
  • Basement is walk-out and there's no radon

There are 2 HVAC systems (both sitting in the basement):

  • The larger (100kBTU) system is zoned for the 1st and 2nd floor.
  • The smaller (40KBTU) system is zoned for a large south-west facing 1st floor office with many widows and the basement.

In the summer, the cool air sinks to the basement, and the heat must run to keep it at 69F. If I turn off the basement zone, the basement eventually settles at around 64/65. Heat seems to rise to the 2nd floor open space, where it's usually at least 80F at the ceiling when the AC is set to 75F.

This 2nd floor common space has a return at the top of a wall near the ceiling (conveniently right near the attic entry), and seems to be the hottest place in the house. I'm thinking of disconnecting this return in the basement, and using a Tjernlund M6 duct fan to move that warm air down dispersing it through the basement near the floor.

I'm hoping this would essentially circulate the hot air to the basement, pushing some of the cold air up. Or, potentially it could be done in reverse (move the cold air near the basement floor to the 2nd floor ceiling). Would this help? I don't want to have to run the heat in the summer, it seems like a waste and there's plenty of hot air around.

The Tjernlund M6 moves 500CFM and even at a higher static pressure (say moving 200CFM) it would exchange the entire basement volume throughout the house in 60 minutes. There's also a Tjernlund through floor (ASLL) fan, but this would move 75F degree air from the 1st level floor to the basement ceiling and only provides about 50CFM. It seems moving the 80F degree air from the 2nd floor ceiling to the basement floor would be a better choice.

  • There is usually enough leakage from the system in the basement to do a decent job of keeping the temperature reasonable. But there should also be some registers in the ductwork for the basement. The air handler typically also has an adjustable flap for regulating air to the different branches. If the basement has been finished, might the ductwork vents (and return?) have been sealed off? – fixer1234 May 7 '17 at 20:34
  • Your house sounds like a deathtrap in the event of a fire, with free air circulation between all three levels. I think your scheme would work best with pumping the cold air to the second floor ceiling, but you could try it both ways and see which works better in practice. – Ecnerwal May 8 '17 at 2:49
  • @techiejohn moving your hot air from the 2nd floor to the basement is probably a good idea and it seems you have the duct work to make it easy on you. As for pushing the cold air up - that will probably not occur hot air rises, cold falls. Make sure you pipe the hot air to the floor area of the basement. – Ken May 8 '17 at 3:52
  • Not sure how this is any more of a deathtrap than running the HVAC fan all the time, which also moves air between floors. – techiejohn May 8 '17 at 22:05
  • I already have ducts in the basement. The problem is that if I want the basement temperate to be anywhere near the rest of the house (75 house, 72 basement). The heat would have to run a lot. It already has to run in the summer just to keep the basement at 69 (which it does through the registers installed in this finished basement). – techiejohn May 8 '17 at 22:06
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I live about 30 miles north of Pittsburgh, Pa. so I am familiar with some of your problems. First: the office and basement should not be on the same zone. Since it is installed this way it may be impossible to change now. In summer the office needs lots of cooling to offset the southwest facing windows and the basement needs none or even some heating. Add returns, 2 or more, or as many as you can at the floor level in the basement, connected to the 1st. and 2nd floor unit. Do not disconnect the high wall return near the attic access, but add more if you can to take the hot air off the ceiling. Run the fan for this unit continuously, 24 hours a day on a low speed when the unit is not calling for A/C, to help recirculate the cold basement air. Close any basement supply registers in the summer when the A/C is running. Consult a roofing specialist to see if it would be advantageous to add a roof mounted, thermostatically controlled, attic fan, to vent the excess heat from the attic area. You said that every room has cold air returns. Are there both high and low returns in each room? If so, the highs are used in the summer and the lows in the winter except in the basement. Multiple story homes with open stair wells, open to all floors are very hard to heat and cool. All the heat rises and the cold air falls, as you well know. In my experience adding Tjernlund fans to circulate air is just another noise you will have to contend with. Hopes this info helps. Good luck, in solving your problems.

  • Office and basement are separate zones. The smaller system has 2 zones, 1 for the office, and 1 for the basement. This was recently installed specifically because the office temperate would be wildly larger than the rest of the house (because of the south west facing windows). The walkout portion of the basement faces north. – techiejohn May 8 '17 at 22:09
  • Yes, there are high and low returns in every room. I saw a YouTube video where someone cut a hole in the return of the HVAC to pull the cold basement air and circulate it through the house. I'm wondering if this is a better first step? – techiejohn May 8 '17 at 22:10
  • That is, take the returns of both the large and small systems, cut a 6" hole, and duct as a cold air return to the basement floor (this should be easy since both systems are in the basement already). Thoughts? – techiejohn May 8 '17 at 22:11
  • Since the hottest area of the house is the 2nd floor I would take the majority of the basement return air for that unit. Do not be stingy on the number of basement returns and remember to add extra returns if possible to the area near the 2nd floor ceiling. Cutting holes in the return ducts are OK if they are near the floor and there are no doors between them and the basement area. As I said in my 1st answer, it will be very hard to control the temps between the top and bottom floors due to the house construction. – d.george May 8 '17 at 22:31

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