Basement Cold Air Return

brockmiera · 01-17-2013, 03:25 PM

So I have a ranch house with a full basement. The basement is unfinished but has diffusers in each of the "room" off of the main trunk line.

In the upstairs I have two cold air returns. Both in the hallway and maybe 3' from each other.

My question is do I need a cold air return in the basement too? If so can I just put grate on the bottom of the cold air return from the main level?

brockmiera · 01-21-2013, 01:59 PM

Someone out there has to have worked on a 1950's ranch with full basement before. The basement is quite warm even in the coldest weather we've had here this year. I'm just worried that when I put up walls and finishes that it might change.

Doc Holliday · 01-21-2013, 02:10 PM

you can never do any any harm to an hvac system with more return air. now days in new construction homes, wherever there is a supply in a room there is as well a return.

you can add a return in the basement and it will feel much more conditioned than with simply supplies. if the air isn't moving to and through the system than how's it being "conditioned" in the first place?

brockmiera · 01-21-2013, 02:18 PM

Quote:

Originally Posted by Doc Holliday

you can never do any any harm to an hvac system with more return air. now days in new construction homes, wherever there is a supply in a room there is as well a return.

you can add a return in the basement and it will feel much more conditioned than with simply supplies. if the air isn't moving to and through the system than how's it being "conditioned" in the first place?

That makes sense. How would I go about doing this? Should I simple add an air diffuser ( i think they are called that) Into the existing air returns from upstairs?

The ones from upstairs just use the floor joist cavity now. I can get some pictures up tonight.

Doc Holliday · 01-21-2013, 02:30 PM

cut into the return plenum itself, located at the rear of the system, with a collar. attach a duct from there to the newly installed return air grill wherever you can mount it in your basement.

can you take some pics so we see what you do?

drtbk4ever · 01-21-2013, 03:37 PM

I was told that the best location for the returns is at floor level where the cold air sits. So maybe you could run the duct (as per Doc's suggestion) down one of your new wall cavities to a return air grill at floor level.

brockmiera · 01-21-2013, 04:09 PM

I'll get some pictures here in a few hours. What do you want pictures of? I'll get one of the entire basement, one of the existing returns, one of the furnace. Anything else?

JScotty · 01-21-2013, 04:53 PM

Quote:

Originally Posted by drtbk4ever

I was told that the best location for the returns is at floor level where the cold air sits. So maybe you could run the duct (as per Doc's suggestion) down one of your new wall cavities to a return air grill at floor level.

I generally prefer them high, mainly because low you tend to get a lot of dirt sucking off the floor. Low is generally better for cooling as you're pulling colder air, high is better for heating.

Also another reason to consider returns in every room is pressurization. When you force air into a space & don't pull back out the space pressurizes. So when you try to open the door air will rush out and actually make the door harder to open. Also why doors somtimes close themselves.

concretemasonry · 01-21-2013, 05:13 PM

It all depends on the house design, use, what areas are finished and where you are. It is not as simplistic as a prescriptive code that is just a minimum. I have had many home with basements with finished basements an cold air returns are the best investment in a basement are what you can do if you have a good HVAC system with variable seasons.

We have a 2 story home (lower level is finished and conditioned and partially buried) with an open stairway(chimney effect) and run the fan 24/7 in the winter(heating season) and on auto fan in the winter for comfort. Yesterday, the temprature went from 40F at noon to -&F this morning and my wife left and immediately came back in and yelled saying I did not tell her it was cold outside, so she needed gloves. Tomorrow is will be -15 in the AM with a high of -2F. Nothing will change inside and it will be comfortable because we use good circulation and thermal mass of the soil/floor for comfort and economy. Our annual heating is lower than AC in MN and there are no humidity and dust problems because of cheap 1" filters changed ever 1 to 3 months.

Low cold air returns are absolutely necessary in a lower level for good cleanliness, comfort and circulation in a home. - Just don't try to out-guess Mother Nature and the weather on a short term basis.

Dick

drtbk4ever · 01-21-2013, 05:15 PM

Quote:

Originally Posted by JScotty

I generally prefer them high, mainly because low you tend to get a lot of dirt sucking off the floor. Low is generally better for cooling as you're pulling colder air, high is better for heating.

Hot air rises, so during heating season, by having your returns high, it is removing the warm air out of the room, not the cool air found along the flloor. A bit counterproductive.

During the cooling season having your returns up high would be a good thing to help remove the warm air from the room.

So it is a compromise. For a basement, which tend to be cooler than the rest of the house, I would want my returns on the floor to aid in heating season.

Quote:

Originally Posted by JScotty

Also another reason to consider returns in every room is pressurization. When you force air into a space & don't pull back out the space pressurizes. So when you try to open the door air will rush out and actually make the door harder to open. Also why doors somtimes close themselves.

Having cold air returns in each room will definitely help to move air through the room.

brockmiera · 01-21-2013, 05:38 PM

All good information. Last week it was in the single digits and near zero for a few days here in Colorado. Although it doesn't usually get that cold it really got me thinking. I was down in the basement scraping the mastic off of the concrete and noticed it wasn't cold at all. So then I placed my hand on the exterior concrete walls and same thing. Everyone from CO on here says their basement is ridiculously cold but mine is pretty warm. Any thoughts on that? I mean it is nice and cool in the summer. Warm in the winter. I don't wanna mess that up by putting a bunch of finishes down there.

brockmiera · 01-22-2013, 10:10 AM

Ok so the first two are the cold air returns from upstairs. The third is a view of half of the basement we are finishing now. the last three are the returns from below.

brockmiera · 01-22-2013, 10:11 AM

The Furnace is right behind the small brown wooden door shown in picture 4

Doc Holliday · 01-22-2013, 10:15 AM

Yeah, for ease and simplicity I'd simply cut into the metal backing of the already existing return chase of your hallway from underneath in the basement. This would mean the new basement returns would be up high.

Again, it's just the easiest and most inexpensive and least amount of headache for what's available to do install a return in your basement but yes, it can be done just like that.

brockmiera · 01-22-2013, 10:44 AM

Quote:

Originally Posted by Doc Holliday

Yeah, for ease and simplicity I'd simply cut into the metal backing of the already existing return chase of your hallway from underneath in the basement. This would mean the new basement returns would be up high.

Again, it's just the easiest and most inexpensive and least amount of headache for what's available to do install a return in your basement but yes, it can be done just like that.

Thats actually great news. Since the upstairs return uses two joist bays, do I have to use two joist bays below? It would be more straightforward to use only one joist bay but I can figure out how to frame out to use both of them.