View Full Version : How to block an unused vent

11-09-2007, 06:57 AM
I have two bedrooms that are unused at the moment and for the winter I'd like to fully block their vents to retain as much heat as possible for the rest of the house.

Would it be best just to take the vent covers off, lay fiberglass insulation over the top and push the cover back on? I can't risk actually putting something into the vents as they are vertical and there'd be a risk of it falling.

Is regular roofing insulation OK to use? Other recommendations?

Just closing the vent is effective but still plenty of heat seeps through. I'm not concerned with freezing pipes in either of these rooms, and they'll still get some ambient heat from the rest of the house.

I also have a den with a horizontal vent I'd like to totally block off. The den has it's own fireplace and it's really just the noise of the vent, even closed that is bothersome. It's close to the heater in the utility room and it gets the full force of the blast. That one I could easily stuff with something to completely block it. I'm assuming I can just stuff it with some insulation but please let me know what you think? Thanks

11-09-2007, 07:17 AM
Do NOT use fiberglass insulation.

Fiberglass doesn't stop airflow, just slows it down. And using it to close off a vent, will lead to a lot of airborne fibers - which is really really really bad for you...

Take off the cover, cover the backside with plastic or a cut-to-size piece of cardboard, or duct tape, or... something solid / not porous.

If air still leaks around the edges, use some peel & stick foam weatherstripping.

11-09-2007, 07:20 AM
thanks frenchie, I'm glad I asked ! I'll give it a go.

11-09-2007, 07:26 AM
I'm glad you asked, too - you would have had an itchy winter! :)

11-09-2007, 09:57 AM
Depending on the available access and your willingness to make changes, you could put dampers in the ducts. You should also look to make sure that there aren't already some there.

If you significantly change the outflow of your ducting system, you may need to resize or adjust the flow of the blower motor. Closing off multiple ducts could create much higher pressure in the system, exaberating any leaks and put a bigger load on the fan, shortening it's life and increasing your power consumption. Some fan speeds are adjustable. Higher air flow will mean cooler air into the remaining rooms since it won't linger as long over the heat exchanger.

11-09-2007, 10:31 AM
You might want to keep some airflow going to those rooms. Your exterior walls are much better insulated than the interior walls. If those rooms get cold it's much easier for the cold to creep into your usable living space.

12-14-2007, 10:27 PM
I ended up blocking up a couple of the vents using some of the 'metal' duct tape (not all the way mind you; there is still some air flow). The two rooms are about 10 degrees cooler up there now, but still in the mid 50s.

And I was keeping in mind what jadnashua was saying about the airflow and the size of the motor, etc. but figured it's a big house these two rooms don't make much of a difference.

But one thing I forget... can you guess? The FILTER! I'm a new homeowner and though I have worked with heating systems before this is he first time it's all been my direct responsibility. I moved in last January, and never bothered to check the filter. I found a new one today in the garage and decided to take a look; the old one was incredibly clogged. I switched it out and wow, it's like I just set the system is free. It's actually a lot noisier all of a sudden by the vents, but I estimate the new filter has increased the airflow by over 30 percent!

So, in case there are other idiots out there like me, I implore you, go check your filters right away.

I'm in near disbelief as I type this because the heater came on and kicked off in about 1/3 the time it normally takes to bring the house up to temp... I'm cringing on the possible damage I've caused; not to mention the safety risk. And I'm also thinking how much lower my heat bill would have beenů