DIY Home Improvement, Remodeling & Repair Forum

DIY Home Improvement, Remodeling & Repair Forum (
-   HVAC (
-   -   Crawl space idea...good or bad? (

cdelsig 08-09-2012 04:22 PM

Crawl space idea...good or bad?
I'm renovating a house that is 67 years old. Not in terrible shape, but there are relatively minor issues with the plumbing, wiring, etc. Okay, a new septic system isn't relatively minor, but I'm going to contract that out.

My first question pertains to ducting. I know there is a supply, and there is a return. I also know that a crawlspace has to be insulated and vented in some way shape or fashion. Currently, there is no foundation insulation inside, and no insulation under the floor joists. The only part of my house that is on a crawlspace is an addition to the original house, which has a basement.

There is feed and return ducting going through the crawlspace at this time, along with water lines (supply and waste) for the bathroom, which is the only actual "room" above the crawlspace. Obviously, that's not the most efficient way to heat a house (currently forced air gas heat and room a through-the-wall A/C unit).

If I were to insulate the inside foundation well, would I be able use that space as a "return tank", bringing all the return air into that space, and then ducted to the furnace? This would keep the crawlspace heated to a point (and A/C-ed once I upgrade) and would also allow for the removal of any water that seeps up from the ground. Plus, any ducting and plumbing to the bathroom would go through this moderately conditioned space, too, leading to less heat loss for those runs.

I appreciate the advice and look forward to getting more wisdom in this area.


nealtw 08-09-2012 05:31 PM

There are those that like the idea of conditioning the crawl space. I am not a believer, I think you would be better to box in the the pipes and ducks and insulate all that with the floor and let the crawl space breathe. Your idea of dumping the air in there sounds good like capturing all that cool air in the summer, but what about fire stopping or what happens if something goes wrong and you have six inches of water down there?
BTW, welcome to the site.

cdelsig 08-09-2012 09:58 PM

Thanks for the welcome. The crawlspace would be "breathing" by having the return air dumped into it and then fed back into the furnace. Essentially, it's a mighty big section of ducting there. It would not stay there. Return air would come from the rooms in the house, into the crawlspace and then continue on (mixed with the air in the crawl space) to the furnace.

And, six inches of water down where?

nealtw 08-10-2012 12:01 AM

Draw a picture of the shape of the basement with the furnace location and crawspace. Now put an X where the return air will enter the crawl space. Draw a straight line from the X to the door from the crawl space and the to the furnace. That would be the air movement. The rest of the crawl space will not have air movement. In the winter the return will deliver warm moist and dirty air to the crawl space. As the air there will be cooler, the moisture will condence there and leave dust and moisture there. As far as 6 inches of water, maybe not, but septic systems back ups, perimiter drain fairlure, roof leak. The open hole for fire in the basement to climb to other floors instantly is the big problem.

cdelsig 08-10-2012 05:40 AM

Excellent points. I had considered the air flow, and was thinking of dumping the return air at the furthest point from the where it would re-enter the duct to the furnace.

I don't foresee much of an issue with the septic system, as I'm having to get an all new system installed as part of the renovation. That could still prove to be naivete as I've never lived in a house with a septic system.It's always been sewers.

What would the difference be regarding the fire stop? Is it because I've opened the ducting and previously, the ducting would have provided the fire stop (or at least slowed the spread)? the crawlspace has 4 block walls as it is under an addition to the original house. The space won't be "open" to the basement (the opening is a former foundation window that is approximately 32" x 24") as I will be putting some sort of custom panel there around the ductwork.

I'm not trying to be obstinate, at least not purposely. The way the space is now, I can't see how two vents would be adequate air flow and how I'm going to separate that area from the basement (the former owner had a piece of 1/4" MDF poorly customized to fit the area, but no other seal) and will have to add any insulation since there isn't any now. I'm really trying to make an innovative solution to a poorly contrived system. I'm trying to make things orderly and easier to troubleshoot and repair. Essentially, this house needed a lot of rehab and most everything is going to be replaced.

Thank you for the attention you are putting into my questions. I'm not intending to be difficult. I'm just very, very green with this.

nealtw 08-10-2012 07:30 AM

Where ever posible fire stopping should hold the fire back for 30 minutes for you to get the family out. As you are doing lots of changes in your house, you have the chance to
correct alot of things, firestopping should be on the list throught the house.

All times are GMT -6. The time now is 07:41 PM.