I'm going to be adding 3 cold air returns in my newly finished basement. (I have 4 heat ducts going there already) All of the current air returns have very short runs from upstairs and all go into the top of the main air return duct near the furnace.

The returns in the basement will have to go further distances than the ones coming from upstairs. Will this cause them to not work as well?

Is there any reason they need to go into the top of the main return duct? Can I put the new ones into the side of that main duct just the same?

Thanks,

Returns cannot be placed where you feel like. Duct design has to be done. This is called a "Manual D" calculation.

Returns cannot be placed where you feel like. Duct design has to be done. This is called a "Manual D" calculation.

ABSOLUTELY!

Improper ducting can (and most likely WILL) result in misery, woe, and general unhappiness. Call a contractor out (use the company you've already used and trusted) and have them tell you where and how to place the ducts.

If you don't do it right at this stage, you (and your spouse!) will be kicking yourself for not having done so 2 years from now.

If you have a good relationship with your heating and cooling contractor, they may just come out and do you a freebie, depending on how complicated it is.

K, I guess no one wants to answer my actual questions but just offer their comments. The basement is already done (without the help of any contractors) The heating ducts were already in place by the original builders in the unfinished basement 5 years ago but they didn't do any cold air. I'm adding them to the one bedroom in the basement and one in the main room on the only wall that is an option. Thanks anyway

K, I guess no one wants to answer my actual questions but just offer their comments. The basement is already done (without the help of any contractors) The heating ducts were already in place by the original builders in the unfinished basement 5 years ago but they didn't do any cold air. I'm adding them to the one bedroom in the basement and one in the main room on the only wall that is an option. Thanks anyway

Unfortunately, we have already answered to the best of our capabilities. There are too many variables in ducting that can affect system performance, thus our vague answers and referrals to contractors. Measurements need to be taken, the distance of runs, number of turns, diameter, blower capacity, btuh output of furnace, etc. etc. etc. There are reasons the HVAC industry has established the Manual-D, and this is one of them.

You can not possibly find the answers you seek here with the limited information you offer, and I doubt that anybody wants to get involved in teaching ducting principles and airflow properties to a layman-it's difficult enough for the professional.

A heartfelt congratulations on your successful remodel, but as many others, I think you may have put the cart before the horse here. The ducting should have been figured out first and then the construction done. I wish you well, but you may be in a bit of a pinch here. Sorry.

You can cut the returns in the side of the plenum, it won't make any difference, the longer duct runs in the basement will have more resistance to air flow and this is where proper sizing comes into play, normaly you can't oversize the return duct unless you are trying to move more air from a certain part of the house then the rest of the house. Hope this helps, Mike

Any return you can get from the finished basement will help. If its as small as 4 inch or as large as 10 inch, its better than none. It may not pull as strong as the others but it will help with your air exchange.