Retrun air pathway through crawl space

[mchild]

Is it at all reasonable to have a return air path unducted through a crawl space? The foundation is sealed to the outside with foam insulation and so the crawl is considered conditioned space. It has a full vapor barrier.

My home needs to have return air from the front of the house to the air handler in the furnace closet in the middle of the house. With the joist lay out, and the construction techniques of an old farm house (1889), it is impossible to install ducting and a return grill in the front of the house. The furnace closet is located in an area that is built on slab. Right next to the furnace closet is the kitchen and going through an unused section of a kitchen cabinet and the floor under it would provide access to the crawl space. The crawl space is very shallow.

The idea is to install a return grill under the stairs going to the second floor, which is at the front part of the house. Under those stairs are stairs going down to a hand dug cellar in the center of the crawl space. The grill would provide a pathway to the stairway going down to that cellar, which in turn is open to the crawl space. Then the air could be pulled through the crawl space to the opening in the floor from the kitchen and into ducting that would take it to the air handler.

The distance from the return grill through the crawl to the opening in the floor would be about 20 feet. The ducting would be about eight feet and would be sealed to the kitchen floor. Filtration would be at the air handler.

[Moose]

Duct it if at all possible.... make it possible. healthier by far.

[crmont]

Is the existing return pulled through the crawlspace?

[mchild]

Is the existing return pulled through the crawlspace?

Currently there is a single return at the extreme rear of the house. It is in a new section of the home added about 10 years ago. There are more supplies in the front so getting a return to the front has been generally viewed as a way to improve the overall comfort on the first floor. The crawl space for that new section is not part of the crawl space of the old section. So, we need more return air and getting it from the front of the house is where it needs to come from.

Every contractor that has looked at our setup said there wasn't any other place to put a return except for where it is at the back of the house. Then one suggested this approach, but admitted he had never done it before and wasn't 100% sure how effective it would be, but thought it would work.

Since I now run a dehumidifier in the hand dug cellar, I thought this might be a way to get the return in and keep the humidity in check at the same time.

[karsthuntr]

IMC allows this type of return as long as crawl is sealed completely. I wouldn't recommend it though.

[dash]

Some codes would not allow it,as there would be flamable wood in the return duct,instead of class one duct.

[ELEDSALL]

Is there anything wrong in general with using a sealed crawlspace return plenum? If this is a sealed crawlspace and meets the 25% volume test of the IRC, why won't this work well? A sealed crawlspace has to meet certain ventilation requirements. Wouldn't this just be killing two birds with one stone?

[karsthuntr]

Is there anything wrong in general with using a sealed crawlspace return plenum? If this is a sealed crawlspace and meets the 25% volume test of the IRC, why won't this work well? A sealed crawlspace has to meet certain ventilation requirements. Wouldn't this just be killing two birds with one stone?

You are adding volume to a house that now needs to be conditioned and for a couple more gallons of gas you can add duct work. This means a smaller unit and fewer problems.

[cem-bsee]

one can put a return grill in the floor, like in my Daughter's 1914 house --
then duct it anywhere --
you need to decide where such would be acceptable & out of the way of furniture.
or, give up some closet space & have a box inserted to allow the return grill be in a wall spot.

either way, plan on a 4" thick filter in grill-- BUT the duct work needs to be redesigned.

[r22jjc]

might be some safety concerns if you have any gas fired equipment in the basement.your asking for trouble with an open return from under a building.your gonna lose some control of what enters your home,even with a vapor barrior down your gonna pull moist air,dust,bugs and anything toxic from down below.how low is the crawl space?

[bobb25]

Sometimes “Ya gotta do what ya gotta do”. Old houses can have walls that are impossible to go through or around. You need to get adequate return air back to the unit. At the minimum, you should have return duct capacity equal to the supply ducts. It’s better to use an insulated crawl space than to use inadequate ducting.

[mchild]

Thanks all for the responses.

Sounds like there are two main issues - building code and functionality. In my area they are generally fairly loose on building code issues but we will have to check to see how they would deal with this issue. But, assuming they follow IMC then the issue is functionality.

To answer some of the questions posed. The crawl space is about 600s.f. and ~8 inches deep while the hand dug cellar is 9'W x8'L x6.5'H. So, yes there is some additional volume of air to be handled. But, this is air that needs some conditioning anyway to control humidity.

The first floor of the home has no closets so boxing out inside one for return ducting is not an option. Plus, getting ducting in the small crawl space seems to be the main issue as the waste line passes through the middle of where the ducting would go if it could be put in. Thus, it is using what little space there is. The contractor believes he can get into the area where the floor would be opened to at least put in a grill to minimize larger stuff getting into the ducting. Plans would be to have a large 4" media filter at the air handler. More frequent filter changes are a recognized possibility.

[bobb25]

I didn't see where you mentioned what type of system this is. If this is for an oil furnace or a gas heater without an inducer, then you will need duct work. Some inspectors are a PITA, and have no common sense or HVAC experience. If you are going to contact your local inspector, just call them and get a general feel of what they think. Don't let them know who you are.

[mchild]

I didn't see where you mentioned what type of system this is. If this is for an oil furnace or a gas heater without an inducer, then you will need duct work. Some inspectors are a PITA, and have no common sense or HVAC experience. If you are going to contact your local inspector, just call them and get a general feel of what they think. Don't let them know who you are.

Oh yeah, I forgot to mention that there is nothing in the small cellar that would emit fumes and the system that is being installed is a heat pump that will be replacing an oil furnace. There is a LP gas power vented water heater in the furnace closet.

[Dave-B]

I would be concerned that this would become a Plenum or "other space used for enviromental air". If this is the case then you should be aware that you cannot have any wiring in this "plenum" per the national electrical code.