troubleshooting furnace
December 14, 2011 8:32 AM   Subscribe

The house I rent has forced hot air. There is a broken register on the side of the furnace which is stuck open, blowing hot air into my basement which I barely use. Can I tape this closed w/ some foil tape or do I need to replace the register? Or should I leave it open for some reason?
posted by pilibeen to Home & Garden (15 answers total)
The venting for my furnace has a register in the basement too. When I had a service professional down there two years ago I asked him about it and his response was "do you want to heat the basement?" To which I said no and he said... "then you can close it".

I am not a HVAC pro and this is not HVAC advice. YMMV.
posted by FlamingBore at 8:38 AM on December 14, 2011

I've seen magnetic register covers at the store.
posted by bentley at 8:40 AM on December 14, 2011 [4 favorites]

(Sorry, I hit Post too soon.)

For instance,
posted by bentley at 8:41 AM on December 14, 2011

I'd use the metal/tape wrapped insulation and cover it, or use the register cover suggested. Whichever is cheaper.
posted by rich at 8:43 AM on December 14, 2011

You can probably close it. Only reason you might want to leave it open is to control humidity in the basement, but that might be more efficiently done with a dehumidifier. (And it's probably more important in the summer anyway.)
posted by Kadin2048 at 8:50 AM on December 14, 2011

The energy assessment folks taped mine closed with foil tape. They also sealed the duct joints with some kind of putty if you want to get super efficient.
posted by victoriab at 8:53 AM on December 14, 2011

My husband is a HVAC professional, but he is not your HVAC professional. He has used foil tape to close off the registers in the house in rooms where we don't need much heat.
posted by drlith at 9:04 AM on December 14, 2011

You can certainly reduce the airflow into lesser-used spaces, but I'd be cautious about turning it off completely. Cooling the basement off too much can move the dewpoint into the inside of the wall. This causes condensation on the walls and so can promote mold growth.

If, after taping, you find you walls are damp, you may want to open the register up a bit again. A friend of mine did this and ended up with a quite expensive mold abatement bill when he discovered the problem.
posted by bonehead at 9:08 AM on December 14, 2011

In my old office we used the magnet covers to block vents that blew directly onto the desk. The nice part about the magnet is that they are not permanent and don't leave behind any residue.
posted by teleri025 at 9:30 AM on December 14, 2011

As long as you still have regular air circulation throughout the basement you'll be fine. Aluminum tap eis what is used for this if the register is broken, or the magnetic covers. Both are fine, although the tape may be a challenge to get off cleaning if it's attaching to a painted surface.

My office is in the partially finished basement of our house, we also have a bathroom down here so we keep the registers in the adjoining rooms slightly open to keep air circulation going and to insure the floors above us don't get too horribly cold as our 1 year old refuses to wear socks.
posted by iamabot at 9:54 AM on December 14, 2011

There may (should?) be a lever on the duct work back near the furnace that will close it off at the source.
posted by COD at 10:06 AM on December 14, 2011

Where the air pressure is strong, and that most likely includes your basement, the magnetic covers sometimes don't work well. They get blown off, or at least moved around so that there is major leakage. I have found the best solution is to remove the register, put heavy duty foil, or several layers of foil, on the inside of the register and then replace the register. The structure of the register will provide sufficient support to prevent the foil from moving, bowing out, tearing etc. It works very well and you can achieve a complete seal. If you want at least some small amount of flow into the space you can create an opening in the foil over a portion of the register. In one room I left the central 10% open and it worked well.
posted by caddis at 10:20 AM on December 14, 2011

Used caddis' method since I had everything on-hand. Took just a couple mins and seems to be a good seal. Thanks for the help everyone!
posted by pilibeen at 11:16 AM on December 14, 2011

Don't block the register without asking your landlord! It may well be always open for a reason: to heat water pipes, for air balancing through the system, to reduce noise, for moisture control etc. I have an always on register in my basement and a return in the basement too. They increase overall flow through the system, improve efficiency and reduce noise as well as adding a layer of freeze protection to the main cold water pipes. The system was purposefully designed and built that way. I'd be very annoyed if someone permanently blocked part of the system off.

You're not saving any energy by closing forced air registers. The fan pushes the same amount of air no matter what. You are just making the system noisier as more air gets shoved down fewer pipes and you're creating cold spots that will precipitate damp.
posted by fshgrl at 11:57 AM on December 14, 2011

fshgrl writes "You're not saving any energy by closing forced air registers. "

This isn't true; at least in the general case. Imagine the simplest case of a house evenly divided into just two rooms only one of which contains the thermostat. Completely blocking hot air from going to the room without the thermostat would roughly cut your heating bill in half. This is because even though the furnace uses the same amount of energy when running it would only run half as much.

So in the case where blocking the basement register reduces the temperature of the basement then pilibeen would indeed save energy and money. As other have said care must be taken that they don't save so much energy that moisture becomes a problem or pipes freeze.
posted by Mitheral at 7:27 PM on December 14, 2011

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