How to prevent/slow heat from rising up stairwell?
Hi all,
I have a two-story home with a forced-air electric HVAC system. Heat is provided via a heat pump, with the air handler in the attic. The supply registers on the first floor are in the ceiling. The house’s return is in the ceiling of the second floor.
I’ve noticed that hot air coming out of the first floor ceiling registers tends to stay fairly close to the ceiling and then travels straight up the stairwell to the second floor. This means the first floor is difficult to maintain temperature and the heat pump is constantly working, while the second floor is always warmer than the thermostat temperature setting. I know heat pumps are fairly efficient, but it runs constantly in cold weather and the auxiliary heat frequently runs to keep the first floor warm.
Does anyone have tips/tricks for slowing hot air from traveling upstairs? I have a fan in the stairwell and run it in the winter to force hot air down; I’ve also tried to plug up any cold air leaks on the first floor.
Thanks in advance for all thoughts/comments/suggestions.
– Mike
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Replies
Mike,
Your heating system is poorly designed.
To answer your question: The only way I know to prevent heat from rising up a stairway is to enclose the stairway and install a door at the bottom.
As you may know, an air handler should never be installed in an attic unless the attic is an unvented conditioned attic. If your attic is vented and unconditioned, that's Problem #1.
The more serious problems are (a) your house would benefit from two zones -- a downstairs zone and an upstairs zone -- on separate thermostats, and (b) the registers on your first floor should be located in the floor, not the ceiling.
The least expensive solution would be to install a ductless minisplit to handle your downstairs heat. Set the thermostat of the minisplit to 72 F (or whatever temperature you want), and set the thermostat of your forced-air system 5 or 10 degrees lower.
Performing air sealing work on your home's thermal envelope will reduce the severity of your problem but not eliminate it.
Some improvement may be had with smaller register boots and using register grilles designed for better "throw", angled downward and away from the stairwell. The narrower register opening increases the velocity to enhance both the distance of the throw and the overall mixing.
Oversized ceiling diffusers will tend to keep the warm air near the ceiling plane. That works OK during the cooliing season when the natural convection of the heavier cool air will automatically do the mixing, but it's your enemy during the heating season, resulting in the short-circuiting you are experiencing.
I was faced with a similar issue in my split entry. The basement heat pump is pointed almost directly at the stairs to get heat to a large area on the other side of the stairs from the heat pump.
I took my cue from heat traps for water heaters. The goal isn't to stop all air flow, the temperature differential will be very low, but to stop the heat flow. I installed a curtain at the bottom of the stairs. It's kind of crude looking and could certainly be made more attractive, but it's better than a door in my mind. (Honestly this is one of those "lets put this up temporarily for testing and I'll make it pretty if it works." projects. The problem is I still haven't made it pretty...)
So far it seems to be working brilliantly, the stairs is the coldest part of the house now instead of the hottest.
imgur dot com/a/sAtpi
Dear Martin, Dana, and Calum,
Thank you all for your helpful responses. This Q&A platform is such a valuable resource.
Mike
Commercial buildings handle this (I've done it in my home) with smoke baffles. They're primarily meant to mitigate smoke traveling up a stairwell but the same premise can be used for heat mitigation and can be installed in stairwells with lots of heat movement (in a main area of the home or near central vent)