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I have a forced hot water (baseboard) heating system in my home and added central air conditioning about 10 years ago. The cooling system's air handler is in my attic, and duct work was added for the 1st and second floors for cooling. There are 3 returns on the 2nd floor, and about 10 supply vents throughout both floors.

My question/issue is that two of the returns and 3 of the supplies have pretty bad (cold) drafts throughout the winter. I measure the temperature at around 50 degrees F on them. All the others are at/near room temperature.

I'm considering blocking them for the winter months by purchasing covers, or likely a DIY project like http://www.instructables.com/id/Winter-HVAC-Hack.

My main question is that should there be any drafts at all. Are the drafts a sign of duct leaks that should be found and repaired by the HVAC company?

  • Does your air-con unit have a heat setting? Many do, and it may be cheaper than using the baseboard heating, depending on the energy source. – Someone Somewhere May 2 '16 at 9:49
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The air in your duct work is cold because it is running through the attic which is not heated. There will be some air flow through the ducts because they are not a "sealed container" they are designed to move the air in your home.

As for the DIY project if your covers are metal I would suggest using a magnetic tape or adhesive sheets to attach them. Or they make covers:

For the ceiling registers you will want to make sure the magnets are strong enough to hold material tightly.

  • What I find confusing is that there seems to be a random set of drops/returns that have a lot of cold air coming out of them and the rest have none (as verified by my laser temp reader). All the drops have slats that I can shift to close most of the air passage. Should blocking all the returns (that don't have movable slats) be enough? – tmcallaghan Jan 3 '14 at 20:06
  • With out knowing your specific duct design it would be hard to know why some do and some do not. Blocking the returns that are moving cold air should do the job. – BD72 Jan 8 '14 at 21:00
  • Thanks. I've blocked them all with home made covers that I secured with zip-ties. – tmcallaghan Jan 9 '14 at 14:45
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I had the same problem with cold drafts coming thru the ac vents that are not used for heating in the winter (I too have baseboard hot water heating and only use the ac and ducting in the summer).

I have 3 returns and a lot of supply vents and covering each one individually would be time consuming and not practical.

Instead I pulled out the filter from my air handler (which like yours is also in the attic) and covered it with plastic sheeting. This blocked the air circulation between the returns and supply vents and eliminated the drafts.

I have not heard of others using this method but it worked very well in my situation.

  • Sounds like something worth trying (blocking the system) but mine won't be as easy I only have electrostatic filters not something I can easily cover up. – tmcallaghan Jan 5 '18 at 15:44
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Go buy a new filter. They are shrink wrapped in plastic. Pop it in, come cooling season you have fresh filter waiting for you.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. – Daniel Griscom Oct 15 at 3:17
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A few months ago when we bought our home, I immediately noticed the cold air flowing in through the ceiling AC vents and particularly where the "20" by "20" filter is located in the ceiling. (It's a bummer to change because it is located in the ceiling at the top of the stairs...one false move and I'm going to be in a dozen casts!) Anyway, I did exactly what was suggested in reply #3 above and what a huge difference it made! For my other small ceiling AC vents that also leaked badly, I closed the vents with the little "handle" as best I could and yes, cold air still leaked through, though somewhat reduced. The vents are not magnetic so commercial "magnetic" products were not an option. So, I took large zip seal FREEZER bags (thicker plastic than non-freezer bags), sliced them on all 3 seams and got 2 small "cheepo vent covers" from each bag. I had to trim them a bit for a good fit on the vents. I put clear packing tape on one edge of the sliced bag, taped it to the metal part of the vent (avoiding the ceiling paint) and then taped the other 3 sides of the bag) to the remaining 3 sides of the vent, being careful to fully surround the bag and vent with tape, leaving no gaps. WOW. What a difference! Not a fun project to be sure, but cheap, effective and they can be easily removed and reused each year by just replacing the tape.

  • Great ideas. You'd think there is a tremendous commercial opportunity here. – tmcallaghan Mar 12 '18 at 11:55

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