Thread: intake in crawlspace

Can you have an air intake for a high efficiency furnace in a crawlspace?

54541.jpg

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You would need to check the manufacturers installation instructions.
Of course the crawl space would have to be vented with ANY combustion appliance that draws combustion air from the space.

I would say yes, as long as its meets the requirements for no being a confined space. Not much different than a basement, just shorter so less overall volume.

Cory

More info is needed.

Make of furnace?
CS - ventilated to exterior or into basement?
Age of house?

Your picture tells us nothing other than its not vented to exterior.

US Dept of Energy
Furnace interaction with the thermal envelope typically takes the form of increasing infiltration (if the direct vent option is not supported), heat losses through the enclosure and interactions with the distribution system that can lead to duct leakage outside the conditioned space. Highefficiency furnaces use about 10 cubic ft. of air for every cubic ft. of gas burned, or about 13 cfm of air for the typical 80,000 Btu/hr furnace. The increase in heating load associated with the increase in infiltration, if outdoor air for combustion is not used, is on the order of 1% in cold climates, or about 800 Btu/hr in this example. In addition, furnaces that use indoor air for combustion may be competing with draft-hood equipped appliances, dryers, range hoods, fireplaces, and ventilation systems for air, resulting in nuisance heat outages. For this reason, direct vent systems are strongly recommended in this Measure Guideline for furnaces installed within the conditioned space.


PS The update feature on this forum is a pain in the ass!

I looked up a random brand, Lennox, high efficiency gas furnace, and the one thing missing in your pic is a debris screen. If yours was a Lennox, that is.

https://www.lennox.com/pdfs/installa...L193UH_IOM.pdf

Page 22 shows the intake pipe turned down to draw from the crawlspace. But you want to look up the installation manual for the make and model you saw.

So your question is Can you? Yes, you can do lots of goofy stuff. You mean is it allowed or permitted? and it might be allowed but as Jim said, the crawlspace must be ventilated.

And as Raymond said it is a dumass lazy approach to heating your home, at least that is how I read it.

In fact there may have been a pipe or hose taped to that short stub, from the looks of that chunk of tape. If it was me, I would report that the intake pipe from the exterior is missing, have it repaired. Why? because the furnace in your pic is creating negative pressure in the crawlspace, never a good thing.

If there is plenty of open space and air leakage, there may be adequate combustion air available in the CS even if there are no vents to exterior in the foundation.

Again many factors not provided by poster.

Originally Posted by Raymond Wand

If there is plenty of open space and air leakage, there may be adequate combustion air available in the CS even if there are no vents to exterior in the foundation.

Again many factors not provided by poster.

You are right but it is dumb science to draw from the crawlspace. It is cold outside, you are trying to efficiently heat your home. A $20 pipe can give you that efficiency. Instead, you pull cold air in under your floor?

Here is one setup I ran into last week - the intake was inside the furnace compartment and the exhaust had a run of approx. 30 feet with one 90 degree bend. Any thoughts?

Originally Posted by Jim Hintz

Here is one setup I ran into last week - the intake was inside the furnace compartment and the exhaust had a run of approx. 30 feet with one 90 degree bend. Any thoughts?

The manufacturer's instructions would be required to say if the vent is ok. You can usually run quite a distance with 3" pipe.

It looks like a rag or something is covering the combustion air opening in the housing. I would recommend extending the pipe at least to outside of the housing. I suspect that would be required, but again, the instructions have the details.

If handy I take a quick look (and photo) at the instructions so my comments are accurate. If I can easily find the instructions on line, same thing. Otherwise you have to defer to others, which I hate to do.

- - - Updated - - -

Originally Posted by Jim Hintz

Here is one setup I ran into last week - the intake was inside the furnace compartment and the exhaust had a run of approx. 30 feet with one 90 degree bend. Any thoughts?

The manufacturer's instructions would be required to say if the vent is ok. You can usually run quite a distance with 3" pipe.

It looks like a rag or something is covering the combustion air opening in the housing. I would recommend extending the pipe at least to outside of the housing. I suspect that would be required, but again, the instructions have the details.

If handy I take a quick look (and photo) at the instructions so my comments are accurate. If I can easily find the instructions on line, same thing. Otherwise you have to defer to others, which I hate to do.

- - - Updated - - -

Originally Posted by Jim Hintz

Here is one setup I ran into last week - the intake was inside the furnace compartment and the exhaust had a run of approx. 30 feet with one 90 degree bend. Any thoughts?

The manufacturer's instructions would be required to say if the vent is ok. You can usually run quite a distance with 3" pipe.

It looks like a rag or something is covering the combustion air opening in the housing. I would recommend extending the pipe at least to outside of the housing. I suspect that would be required, but again, the instructions have the details.

If handy I take a quick look (and photo) at the instructions so my comments are accurate. If I can easily find the instructions on line, same thing. Otherwise you have to defer to others, which I hate to do.

Originally Posted by Jim Hintz

Here is one setup I ran into last week - the intake was inside the furnace compartment and the exhaust had a run of approx. 30 feet with one 90 degree bend. Any thoughts?

The manufacturer's instructions would be required to say if the vent is ok. You can usually run quite a distance with 3" pipe.

It looks like a rag or something is covering the combustion air opening in the housing. I would recommend extending the pipe at least to outside of the housing. I suspect that would be required, but again, the instructions have the details.

If handy I take a quick look (and photo) at the instructions so my comments are accurate. If I can easily find the instructions on line, same thing. Otherwise you have to defer to others, which I hate to do.

The fresh air requirement is competing with the exhaust given the set up.. Looks like a lot of dirt from back drafting (?) on interior cabinet, bottom right area.