Can I cap a heat vent?

robynpaFebruary 24, 2008

We have a 5x8 bathroom that is too hot even with the one register cover closed. We are in the process of putting up beadboad on the lower 1/3 of the walls. I would like to just seal off this vent and put the beadboard right over top.

How can this be done? The guy at Home Depot said there were things called register caps but that they did not sell them. I have searched the internet and did not find any such product.

This vent/duct in on the top floor and is solid metal at the top of the register cover. So all the air that is forced up just pours out of the vent.

Is this an ok thing to do and what is the best method?


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Whenever you're covering up any vent, you have to consider the balanced airflow system that could be effected. If I were sealing off a duct, I'd want it sealed off right at the trunk line (which is one of the main supply lines coming off the unit) so that the air doesn't try to travel up this run and then stop, possibly causing excess static pressure. Perhaps this duct could be dampered, which means it isn't fully blocked off, but it is partially so that the airflow is limited. Some registers in my house on the middle floor were dampered to balance the system and I guess force more air upstairs. All in all, I'd just call in a professional to give you some advice on this matter. I have a similar vent right near my unit that EVEN WHEN CLOSED pours out tons more air than I'd like. I plan on having this fixed soon, though. Best of luck to you.

    Bookmark   February 24, 2008 at 12:52PM
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Thanks! How do I locate the trunk line to that vent and is sealing it off at the trunk something that I could do myself>

Thanks for your response!

    Bookmark   February 25, 2008 at 1:48PM
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The trunk line could be located in your basement if it's unfinished or it could be hidden beneath the wall. If this is the case, your only other alternative might be to seal it off at the vent. I'm not guaranteeing this won't have adverse effects on the system though whenever you tamper with airflow distribution. It's not something you'd want to do yourself unless you had sheetmetal, screws, mastic sealant, etc.

    Bookmark   February 25, 2008 at 6:09PM
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Duct tape it shut and see what happens. Chances are, you won't even notice it, except your bathroom won't be overheated any more. Then make a sheetmetal cap and permanently install it with screws. You can seal it with silicone. This is not rocket surgery.

"possibly causing excess static pressure"
- That's a good one...

    Bookmark   February 26, 2008 at 3:11PM
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"possibly causing excess static pressure"
- That's a good one...

Someone who has a lack of knowledge about air distribution would say something like this. When you force air anywhere, it's going to find a way out, or it's going to built up pressure. Do you know what static pressure is? The Carrier Infinity system has a special feature that measures this.

To the original poster: doesn't your register have a knob on the side that you can close it off with?

    Bookmark   February 26, 2008 at 4:28PM
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Will closing one vent make a huge difference? Probably not.

I'd be weary of someone telling you to just duct tape a vent shut. LOL

    Bookmark   February 26, 2008 at 4:30PM
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I'm redoing my kitchen and have a similar need. There's a heater vent right over the stove exhaust hood that sits in between the upper cabinets. I have a new cabinet that will need to go over this. There's barely any pressure coming from this vent.

So, what is the best way to cap this one vent to allow me to put the cabinet over it? Cap up in the attic at the branch? If so, how?



    Bookmark   March 14, 2008 at 3:20PM
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Are there any other vents in the kitchen besides this one? If this is the only one, I wouldn't cap it. Is the vent open to allow air to flow out? The lack of airflow is probably due to a poorly designed duct system or a damper not open/open all the way somewhere. Is there anyway to move this vent?

Is the branch line exposed--either in the attic or in the basement? If you could seal the vent off at the branch I'd do that. I just don't like the idea of sealing a vent off right at the end of that duct "takeoff."

Perhaps someone else will have another opinion on this...

    Bookmark   March 14, 2008 at 11:04PM
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You can't cap a heat vent off because if you do, the pressure will build up inside the capped off section until the ductwork explodes. How do you plan to explain THAT to your insurance company?

    Bookmark   March 15, 2008 at 2:06PM
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there are no other vents in the kitchen but the utility room, where the furnace is, is directly behind this particular wall. There's a no door separating the utility room from the kitchen. There's a vent in the utility room as well as in the family room which is directly adjacent to the kitchen. The kitchen sits in between the family room, which has two vents, and the utility room.

I believe I can access the main branch in the attic. I was thinking that if I am going to seal this vent doing it from the main branch would be the best option. This would make me feel better in avoiding any possibility of the heat drying the cabinet(s) out.

Relocating the vent would be fairly difficult as the kitchen is very big and the walls are all covered with cabinets.



    Bookmark   April 2, 2008 at 10:07PM
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For what it is worth. I found this insulated cap that you can easily install or remove if there are any adverse effects.

On an unrelated question. I am enclosing a deck that is adjacent to my boiler and utility room. The utility room gets very warm due to the boiler and hot water heater. Instead of putting heat in the enclosed deck I am thinking of putting in a couple of registers between the two rooms so the hot air can just spill into the deck. The question is if the air will circulate with any efficiency? Would putting registers both high and low cause a natural air circulation of cold on the bottom going into the hot room and hot at the top going onto the cold room?


Here is a link that might be useful: Insulated register covers.

    Bookmark   December 2, 2010 at 9:13PM
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Don't be retarded, its not going to explode regardless. Most branches serve more than one vent, and if its a vent farther down the line it may not be blowing much heat. If there are two vents or more on that branch, then sealing one vent will cause the others to have better hot air flow coming out.

    Bookmark   February 12, 2011 at 8:23PM
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I have a similar problem. I am changing a half bath to a full bath and there's a floor vent that is in the middle of the bathroom that limits my ability to place a shower (about 30" from outside wall). This is the last vent on the line and there is another vent about three feet away in the hall outside the bathroom, which by the way, will now be in the bathroom once it's enlarged. There is very little flow coming out as it is the last vent. Is it okay to seal this off and make the one in the hallway the last one?

    Bookmark   April 6, 2011 at 12:15AM
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Was a little funny reading this. One person is right about air build up, but not if you cover one or two vents. It would never be a good idea to block a majority of vents to a heating system. The heater is designed to operate with a certain amount of air circulation. However, covering up one or two outlets in a system that has ten or more offers little chance of danger, though it would be a good idea to monitor the blocked areas, as well as the heater, during the first few days after redirecting the heat to make sure there are no issues. Ultimately, this is a safe modification to make.I imagine that the original writer resolved their issue, however any of us can make modifications anytime.... happy renovating!

1 Like    Bookmark   September 27, 2013 at 2:26PM
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