Can I shut my upstairs heating vents?

November 18, 2012 2:52 PM

Why are there forced air heating vents in the second floor of my small rowhouse? Won't the hot air just head upstairs and even it all out?

OK, I framed the question a bit simply. I live in a small (1500 sq ft) urban rowhouse with forced air heat. Downstairs vents are in the ceiling, upstairs are on the floor (except in the bathroom).

I've had neighbors tell me to just completely shut all the upstairs vents, since the increased hot air from downstairs just floats up (the thermostat is downstairs). They say that since the hot air is being more "focused" to just the downstairs vents, it's more powerful, or efficient, or something. They all do this in their homes.

To someone who doesn't know better, this kind of makes sense. What am I missing?

posted by kinsey to Home & Garden (8 answers total)

With the different vents upstairs and downstairs, you have the option to have some element of control of the heat downstairs and upstairs.

If you want it colder upstairs, you can shut some or all of the vents upstairs and just allow the hot air to rise (which will happen, but not be as efficient as blowing air upstairs directly).

If you want it warmer upstairs, you can leave the vents all open or shut all the downstairs ones. It gives you some granularity of control.

I think a lot of people like it cooler upstairs, so the slightly inefficient convection of hot air up the stairs gives the same kind of temperature differential that they want anyway, which is why they 'all do the same thing'. We have a 4 floor townhouse and our vents are close in the basement, partially closed in the main floor, all open on the floors above. This gives us the nice warm second floor without over-warming the ground floor and still leaves the top floor cooler just because of how the place works. We'd have to shut more ground floor vents to get it as warm as we have it on the ground floor up there.
posted by Brockles at 3:02 PM on November 18, 2012

If you keep an upstairs room closed and with the vent closed, it won't get any warm air in it.
posted by DoubleLune at 3:03 PM on November 18, 2012

If you didn't use your lower rooms, then you'd want to shut them and only have the upper floor ones open. That might explain why they were built the way they were, even if your neighbors are right. I bet they probably are.
posted by Straw Cab at 3:03 PM on November 18, 2012

This is a frequently asked question of HVAC specialists. This is the most common answer—your HVAC system doesn't know that some vents are closed, causing it to generate excess air pressure for the available vents, which creates leaks in the ductwork, making it even more expensive to heat and cool the house.

If upstairs ducts weren't necessary, they wouldn't be put in homes. But they're universal in multi-story homes with forced-air systems. I had my home built two years ago to (then-draft) LEED Platinum specs, and even among us really hardcore energy-saving types, we've got upstairs vents, and they're wide open.
posted by waldo at 3:07 PM on November 18, 2012

Also, think about the air flow in your home: hot air exits the registers, loses some of its heat as it mixes with the cooler air in the room, and then is drawn to the cold air return for the furnace. Hot air downstairs won't really have a chance to get upstairs (and it'll be basically room temperature by then anyway, which defeats the purpose) because it's all going to end up going to the cold air return.
posted by backseatpilot at 3:46 PM on November 18, 2012

hot air exits the registers, loses some of its heat as it mixes with the cooler air in the room, and then is drawn to the cold air return for the furnace. Hot air downstairs won't really have a chance to get upstairs (and it'll be basically room temperature by then anyway, which defeats the purpose) because it's all going to end up going to the cold air return.

Or, if the return is upstairs or the unit is in the attic or something, it'll suck up warm air wafting up from downstairs so that your upstairs heating isn't very well distributed.
posted by LionIndex at 7:30 PM on November 18, 2012

Also, consider the location of your thermostat. The furnace will cycle off when the air temp reaches the selected temperature at that location. So, even if the downstairs air could rise to heat the upstairs, the furnace may not run long enough to generate the needed warm air.
posted by she's not there at 8:24 PM on November 18, 2012

Also, do you have an air-conditioner in your system? Because, e.g., waldo seems to be dismissing the possibility that the right use of your system is to close the top-floor vents in the winter (heating from below) and to close the first-floor vents in the summer (cooling from the top) -- you need all the vents because all the rooms need some degree of heating and cooling, but everybody's precise solution/preferences will differ. We have a four-floor townhouse and need not only to open and close vents, but to cover the top or bottom floor vents with magnetic panels to make the house work right in winter and summer (where "work" is defined as not baking upstairs or huddling under blankets on the ground floor). Our thermostat is on the 2nd floor, for what that's worth. And, with all of that, my daughter's room (3rd floor) is always cold in the winter, with vent open and roaring. You can't win.

Anyway, the ceiling/floor thing is just a cheap way to handle air distribution (one set of ducts with grates on top and bottom). Adjust things to fit your comfort levels, or adjust nothing if the house feels comfortable to you as it is.
posted by acm at 7:51 AM on November 19, 2012