Sealing Off Heating Vents

[L C]

Is it ok to seal off the vents where the heat isnt needed all that much? When we had our central AC repaired, I asked the guy if this was a good idea, he said it wasnt but I dont remember the reason. With propane going up we will go broke heating our 4 bedroom house this winter. If its ok to seal off the vents in the back of the house we would save a ton of money . We do close the vents but heat still escapes from them. I saw some magnetic vents that would probably work. Thanks

[Heathcliff]

Sure you can. And it can be as simple as cardboard and duct tape. A few things to consider though:

1. Leave enough vents open that you are not impairing the operation of the furnace blower. If you are closing off more than, say, 25% of the vents, you might want to consult an HVAC person.
2. Make sure you will not allow parts of the house to freeze, paying special attention to areas with plumbing.
3. Make sure you don't close off vents in the vicinity of the thermostat. That would just make the furnace run MORE.
4. There may be controls built into the ductwork that allow for shutting off particular areas - if so, that might be a better way to do it rather than covering up vents. If you can, look at the ductwork to see if there is anything that looks like a handle you can turn.

[Blattus Slafaly]

If your inside walls are not insulated and have spaces under the doors all you are making are some big drafts into your house from the closed rooms. This would make your furnace run more.

[trader4]

How is that going to make the furnace run MORE? Say I block off the vents and return to a bedroom that has two outside walls, two inside walls, and one door. Let's say the door has a half inch gap under it. What physics explain the furnace using more energy, instead of less?

[ransley]

You will need to measure the air temp just above the furnace, there is an acceptable amount of temp rise before you overheat and shorten the life of the furnace.

[jmeehan]

There is not easy answer to that one, other than it depends.

Blocking off too many vents will cause a higher than designed load on the fan. That can damage the fan motor. It also can cause other problems like over cooling of the A/C coils which can then freeze over and do damage. The same sort of thing can happen when it the heat is on and it could shout down due to getting too hot.

In the typical home blocking off one vent is not very likely to cause a problem, but there is some point where it will cause problems. Maybe two maybe 10 maybe one. No one here can give you a definitive answer for your home situation.

BTW it likely will reduce efficiency, even if it is a single vent. It may do that even though it may reduce cost.