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

Adding Ducts or just vent to basement

Posted by andrelaplume2 (My Page) on
Thu, Apr 16, 09 at 10:21

Well after 2 years we ALMOST had our new trane system heat pump installed....thats when the dealer became, shall we say, unrepsonsive.

I have a backup dealer and they are coming out with a contract though. One thing I need to decide is ducting for the basement that we are slowly finishing. The 'new' installer has a little bit different philosphy on this so I need some input.

I am finishing my basement, 750 sq ft; adding inslualtion and a ceiling. We currently have no heat down there. It got as low as 52 this year. Today its around 60. I doubt it ever gets above 67 in the summer, if that....not sure though. We are putting in a 3T unit for our 20 year old 2200 sq ft colonial. That should allow for a few ducts/vents in the basement I am told. Consensus has been adding some ducts/vents down there should have an impact but even after insulation and finsishing the basement, it still may need some electric baseboards here and there to take the chill off. I am ok with this. My thought was to add a few ducts/vents and see what happens.

Well, now I need to decide what to do since I am at a point where they will be coming to do the install AND I am ready to box in my main duct lines.

Option 1:
Add about 4 ducts and a return. These would branch off the main, have dampers and eventually release the air thru my dropped ceiling. I am looking at an additoal $400 - $500 for this. This would seem to need to be done now, before I box anything in. I'd likely want to keep the return closed until I was done working down there so as to keep dust out of the rest of the house.

Option 2:
Simply add vents to the main duct line, 2 - 4. Possible add a return too. Cost here is likely $100 or less; I was told I could almost do this my self, even after boxing in the main.

I hate to spend $500 to run ducts off the main if, in reality it will not make much more difference than simply adding a few vents to the main. Also, I may need to close these in the summer if it gets too cold down there so the less to remember to open/close the better. Also, is there any 'added' monthly cost to do it one way or another?

Which way?

Thanks...I sort of need to make a decision today so do not be shy!

Follow-Up Postings:

RE: Adding Ducts or just vent to basement

Of course the correct calculations will need to be made but I think it's a no-brainer to spend the extra and do it right.

The important thing is there'll be cold air returns down there, you may be glad of it in summer since, if it's cool down there, it may help with cooling upstairs.

RE: Adding Ducts or just vent to basement

Well, the second guy was just out and I signed. Based on the layout of our basement he suggested on single duct run (to be done immediately) and 3 vents to be placed in the main duct. He actually reccomended adding them one a time once the cool weather returns thinking I may not need that many. I said I'd pay to have extra runs put in but he felt I'd be wasting my money and the vents in the main duct would suffice. He felt I may need a baseboard or two take the chill off if necesary. Remember, the basemnt is not a separate zone. He said I should box in the ducts and install the vents myself, that it was fairly simple.

He suggested when my basement was complete, to have them back to install a return.

RE: Adding Ducts or just vent to basement

That's gonna be a lot of air coming out of those vents if not done right on the main trunk line. You'll want return air if you're putting supply air down there.

RE: Adding Ducts or just vent to basement

Yes we will need a return BUT with all the cutting/spackling etc (ie mess) it was reccomended NOT putting the return OR vents in the main duct, until AFTER the basement was complete.

The one new duct off the main WILL be run immediately since it is easiest to do it now while everything is still open.

RE: Adding Ducts or just vent to basement


you should insulate this area well. you really need a load calc for this addition. if this area is partially at or below grade, cooling should be relatively insignificant with heating more important. I would be a damper on the supply(s) to control air flow. one return should be OK.


RE: Adding Ducts or just vent to basement

thanks...we are insulating.

RE: Adding Ducts or just vent to basement

Sounds like the carriage is pulling the horse. Apparently there was no heat loss done here before the sale to determine the proper sized equipment first, or all of this guessing would not be happening now. You put the supply ducts down at the floor since warm air rises and you will also need a return at the floor top get the cool air off the floor.
The amount of supply air you need is dependent on the heat loss for that area.
Proper sizing will keep operating costs to a minimum along with less maintenance.

Here is a link that might be useful: FAQ about need for a heat loss

RE: Adding Ducts or just vent to basement

yes, cart pulling the horse to a degree....we are getting the heat pump and doing the basement at the same time...can only estimate how insulated the basement will be, that being said they told me no matter how well I insulated a 2.5t unit was too just barely covered the upstairs. Similarly a 3.5t would be too big. I am confident we got the right size. Balancing it out may be an issue down the road. I agree about the placement of ducts, ideally at floor level though I do not ever recall seeing it this way in a basement....ussually in or off the main duct.

 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