Return to the Heating & Air Conditioning Forum | Post a Follow-Up

How to seal a return

Posted by randy_r (My Page) on
Fri, Jul 9, 10 at 20:07

When I open the door to my basement I can feel air being drawn to my furnace which is located there. So I must have a leak in my return, right? How do I track it down and seal it?

Follow-Up Postings:

RE: How to seal a return

I'll tell you how I did it.

Get yourself a dowel, at least a yard long. Cut a strip of facial tissue about an inch wide and tape it to the dowell.

Then, with system running, run the tissue along all seams, joints, filter housings (where door are) and furnace/air handler doors, and you will know where the leaks are.

One area may be in hiding: if you have panning (check the edges, also), run the tissue along the tops of the trunks where the panning connects, and where the takeoffs are located.

That should do for a start.

Good luck.

Oh yes, I used the duct sealing compound from HD

RE: How to seal a return

That is a great idea!

RE: re: How to seal a return

I'm glad that you liked it. I developed that trick after I tried a tip that I learned on another forum.

To determine if you have a supply or return leak AND you have an attached garage, take a length of string (about 2-3 ft)and hold it next to closed door (leading to the garage). Crack the door open; the string should like perfectly straight.

If the string pulls outward, you have a return leak. Pulling inward denotes a supply leak. The (outer) garage door should be closed.

Oh yes, you can attach the string to the other end of the dowel.


RE: How to seal a return

I know incense sticks work rather well also. I would also pull the return vent covers off and shoot a few pictures down toward the floor in the wall pocket to see how big the hole is for the return air and some towards the sides to see if return air is being pulled between the sheetrock and studs. Hopefully this area has metal duct but if not air can be pulled from anywhere if the sheetrock is not tight against the studs. I did seal mine but it was a pain in the butt.

I do not remember how many square inches of return you need per ton... but you need to make sure you have no majorly restricted area in the floor opening like mine was not even half the size of the stud bay. I had 3x5" holes cut out in 3.5x14" available area which if everything had been sealed up would have caused the blower motor to fail in fairly short order.

I would do the supply side also after the return is done which can also have unbelievable leakage.

Also make sure the blocking is sealed at the top of the return to prevent air from being pulled out of the attic.

I looked up what I calculated for return area.

2cfm per square inch of return grill area. The hole in the floor or smallest flow area needs to be close to half the size of the grill area or larger to keep noise down and allow optimum flow.

You might have to find a place to add a return or might have to turn some 6x14's to 6x30's.

I am no pro and just had to go through a big duct repair job on my system. If any of my calculations or advise are off.. please jump in and correct me.

RE: How to seal a return

Funny yall should be talking about return air... I had a customer who was complaining about a noisy unit, water leaking on the floor and not cooling enough. Turned out his 10 year old system had never been cleaned but we couldnt even get to the coil above the furnace because the door to the closet was only about 6" taller than the top of the furnace. Also noticed something kinda funny about the return air...
Carrier Gas Furnace

Carrier Gas Furnace

The customer said he just about closed off the return air because he couldnt stand the noise of the blower motor when it was running !

RE: How to seal a return

fluffybunny....and you left him that ductboard..or did he buy it on his own? (LOL)
R/A isn't can see air bypassing the filter.
HO should do some caulking and lose the ductboard.

I test with a blower door for house leakage and ducts with a duct blaster(or sometimes flow hood).
You would be amazed at the leaks this methodology uncovers!
Look for spiderwebs as they spin their webs where air moves.
R/A should be caulked, platform that unit sits upon caulked to the walls of heating closet.

best of luck!

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Heating & Air Conditioning Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here