Heating, Air Conditioning, Fridge, HVAC/Adding HVAC register


QUESTION: This should be an easy one for you. For background, I am a long-time DIYer (done lots of simple drywall, carpentry, electrical wiring, and plumbing work), so I should have the "handyman-ness" to tackle this... I just need to know the best approach and (probably) some things to avoid.

15 year old 2600 sf house (we just moved in). Basement is divided about 60/40 (60% unfinished, 40% finished including a bathroom). The finished part has a couple of small HVAC registers running to it and is fine, temperature-wise. The unfinished part has a single small "opening" (just a short section of 4-inch or so diameter pipe sticking down from the plenum). It, however, is in a location that makes it pretty much useless for our goal, which is to get heat to the "main part" of the unfinished section.  

It seems like I should be able to block off that "opening" and put a register in the "main part" fairly easily and without having a noticeable impact on the air flow balance (do you guys still worry about that?).  In the "main part", I have pretty much unfettered access to the plenum and to a couple of branches that feed 1st floor registers.

Is this as simple as it seems? Any tips on putting a register (or whatever is appropriate for a basement setting) in the "main part"? As an example of the type of detail I don't know about: Should the opening be pointing down (vertical) or horizontally?

Thanks for your time!

ANSWER: Add a 10x4 register, installed in a 90 degree register boot connected to the side of the main through a 6" adhesive collar with damper (you can google any terms you don't understand, the parts should be on the shelf at Lowe's, Home Depot or your local HVAC distributor). If that's not enough heat, add another.

Blank off the one opening with sheet metal screwed and taped with UL181 foil tape.

Cutting the register directly into the main will create turbulence within the main, and registers aren't approved for balancing (thus the need for the damper mentioned earlier).

This could change the air balance in the entire home.

If you have a gas or oil furnace, do not even think about putting a return in the unfinished area if it contains the furnace. In fact it would be good to look at the return ducts in the room/area containing the furnace and seal any unsealed joints with UL181 tape or mastic ("duct sealant"). This goes to the risk of circulating combustion products to the living space.

---------- FOLLOW-UP ----------

QUESTION: Thank you for the very detailed, informative answer. Your comment " do not even think about putting a return in the unfinished area if it contains the furnace" gave me pause because the furnace IS in the unfinished area AND there is 4" opening on the "main return body" (obviously my terminology might be flawed) about 5 feet above the floor (and 5 feet from where the filter sits). The opening can be opened and closed with a sliding piece of sheet metal, and there's a sign that says to close it in the summer (inferring that it should be open in the winter). Isn't that essentially a "return"? And if so it violates your "no return in the same area as the furnace", right? It's concerning because of the risk you mentioned and that it was presumably installed that way (that is, it's not some home-made aftermarket doo-dad put on later... based on its appearance).  

One other followup on your recommendation. Is it OK to install the collar & boot at the END of the "main" (what I think is called a "plenum"... the big rectangular section of ductwork which feeds several registers)? I ask because there is a steel support beam in the way on one side, and the "main" is close to the basement wall on the other side, so I might have trouble coming out the side.

Thanks again for your info. If the answers to either of those questions is on your website, feel free to refer me there instead.

You need to blank off the opening in the return - Sometimes I wonder what people were thinking.

Yes, you could connect the register to the end of the main. The register should point down to get the heat to the floor.

Good luck!

PS: There are some images on the "Metal Ductwork" page that might be helpful, and there's probably a bunch of stuff on U Tube.

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Fred Weldin


I can't help you if your whatsis won't work, people (Especially if it's a refrigerator); I have no experience with appliances, and I haven't been involved with H&AC service and repair since March 08, 1996 (Thank the Lord); I always send a "standard" reply to appliance questions and H&AC "Service and Repair" questions (about 20 a month), so if you want to know why your whatsis isn't working like it used to, ask someone else. A lot of my answers arenít read by the questioners; in that event, I always send reminders to read the answers for a month or more (the word "idiots" comes to mind - actually there's another more appropriate word, but discretion prevents its use here). If you have questions about how big a unit you need, if one room's warmer than the others, if you want an opinion oas to scope of work on bids received, etc. just ask. Do visit www.askweldin.com, there's a lot of good information on sizing, ductwork, efficiency, as well as some techniques accomplished DIY-ers can use to troubleshoot and improve their H&AC. Finally, I want to thank all of the kind, serious people whom I meet here: I enjoy working with you. My wife says I'm "snarky" from time to time; as for you others, please use your imagination as to the responses swirling on the snarky side of my brain when I read your questions.


53 years in the business. See www.askweldin.com


B of ME U of D 1965, numerous classes, seminars and a lot of "Hands On" learning since.

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