High efficiency furnace intake in garage

[Darren Buckley]

What are the requirements for high efficiency furnace air intake locations? In theory if the intake is located in the garage, couldn't it pull in gasses from the garage releasing them into the conditioned space?

[Scott Patterson]

What are the requirements for high efficiency furnace air intake locations? In theory if the intake is located in the garage, couldn't it pull in gasses from the garage releasing them into the conditioned space?

I assume you are asking about the combustion air intake and not the return air intake.

The combustion air has nothing in common with the conditioned air in an HVAC system, it is a non issue. Look up the brand you are posting about on the company website and you should be able to find an instalation guideline that shows how the Cat IV intake should be installed.

[Jack Feldmann]

Mr. Wood,
I'm shocked you are shocked at Scott's response. Was there some part that you don't agree with? I assumed that Darren was talking about combustion air, and not return air too.

[Jim Luttrall]

What are the requirements for high efficiency furnace air intake locations? In theory if the intake is located in the garage, couldn't it pull in gasses from the garage releasing them into the conditioned space?

NO, it would not.

[Lon Henderson]

What are the requirements for high efficiency furnace air intake locations? In theory if the intake is located in the garage, couldn't it pull in gasses from the garage releasing them into the conditioned space?
By "intake" you must mean the combustion air intake which draws in air for the furnace to burn. That should not be in the garage and must draw from a fresh air source.

[Scott Patterson]

Mr. Patterson I am shocked with this comment without seeing a picture.

That is why I clearly said "Combustion" air and not "Return" air.... Kevin, don't be so shocked it nothing new and is printed in every install guideline and I think taught in most home inspector 101 basic training courses.

[Scott Patterson]

Scott the reason we need a picture is to determine if the furnace itself is in the garage or the CPVC air supply goes through the wall to supply the High Efficiency Unit. I would still recommend a supply from outside anyways regardless.


Why recommend that the combustion air should come from outside? Not all manufacturers require this and even with a conventional gas furnace the combustion air comes from inside...

[Billy Stephens]

Simply put Scott the air has to come from somewhere, so the house has to provide that air. This does cost money where intalling one from outside has a one time small cost and a gain in many other ways.

OK, I'll Bite.

Please explain some of these "Gains."

[Rick Cantrell]

OK, I'll Bite.

Please explain some of these "Gains."
When you draw combustion air from within the house (thermal envelope), you are using air that has been heated. Since the air was heated, this is a waste of energy. Also, The air that goes up/ out the flue has to be replaced. It is replaced with outside (unheated ) air, through cracks, around doors and windows.

[Billy Stephens]

When you draw combustion air from within the house (thermal envelope), you are using air that has been heated. Since the air was heated, this is a waste of energy. Also, The air that goes up/ out the flue has to be replaced. It is replaced with outside (unheated ) air, through cracks, around doors and windows.

So this intake from the garage is part of the thermal envelope?:(

[Jack Feldmann]

Maybe its because I'm in backwards Tennessee, but we don't usually condition air in garages.

[Rick Cantrell]

Maybe its because I'm in backwards Tennessee, but we don't usually condition air in garages.


So this intake from the garage is part of the thermal envelope?:(

I thought everyone had air conditioners in the garage, I do. Really.
(At one time I tried woodcraft. I had a window unit mounted. I had a really nice sawdust making machine. I could make the prettiest pile of sawdust you ever did see. I did make a cutting board once, but not much else. )

Getting back on topic
I am guilty of thread drift
OP said garage, then as I read on the conversation went to inside the house.
So I was speaking of drawing combustion air from inside the house.
I would still prefer not to draw air from the garage. I spent a lot of money to get that smell of fresh cut wood in the garage. Don't want it to get sucked out.

[Jerry Peck]

Maybe its because I'm in backwards Tennessee, but we don't usually condition air in garages.

And when that is done (it is allowed) the garage system is not permitted to be connected to the living area system, so what little is being wasted would be less than one opening of that big, huge, large garage door ... by the time the operator opens the door, and then closes the door, even for a person to walk through, the wasted energy going up the vent is like a mole hill next to Mount Everest - it is dwarfed in size.

[Scott Patterson]

Simply put Scott the air has to come from somewhere, so the house has to provide that air. This does cost money where intalling one from outside has a one time small cost and a gain in many other ways.

I understand the pros of using an outside combustion air source, but I don't understand why you would call it out/report on it during a home inspection when nothing is really wrong with it if everything else is done properly.

[Billy Stephens]

People count on me to make more than a decision to follow the minimum installation instructions. I recommend what I would want.

That's great Kevin would you show us in this link taken from your web site that states you do this?

International Standards of Practice for Performing a General Home Inspection - InterNACHI (http://www.nachi.org/sop.htm)

[Billy Stephens]

Not needed on the website. It is just one of my elevator pitches. Plus since any client gets direct acces to my Safe Home Guide I make sure any easy thing to do that provides more safety is recommended whenever possible.
I

Just making sure.:(

[Scott Patterson]

People count on me to make more than a decision to follow the minimum installation instructions. I recommend what I would want.

Are you sure that the manufacturers installation requirements are the minimal? What you or I want might not always be the best course of action.

[Rich Goeken]

Mr. Patterson I am shocked with this comment without seeing a picture.
And why would you need a picture?

The answer is correct. The installation manuals that come with high-efficiency units detail the requirements for sizing, methods of installation, locations, and spacing of intake and exhaust. These manuals are usually online at their respective websites. However for your enlightenment, in some cases intake may be in the garage and exhaust may be outside.

Again, I am amazed at your comment.

[Rich Goeken]

Are you sure that the manufacturers installation requirements are the minimal? What you or I want might not always be the best course of action.

Just a sidebar on this. When some contractors bid on a retrofit to a high-efficency system, some low ball by not extending the intake and exhaust to the outside, only the exhaust. But they may overlook make-up air as it may not be sufficient for the installation. An item to be looked at when inspecting.

[Scott Patterson]

Pay particular attention to page 5 and page 10. I have already had quite a debate about this on another MB.
http://www.thecomfortzone.com/heating_air_conditioning/documents/document_library/Furnaces/G1D91BU_G1D93BC_G1D93BU_Installation_Owners_Manual .pdf

That manual is for three models made by LENNOX... Again every manufacturer will have differing requirements and in some cases similar requirements, that is why it is always best to defer to the individual manufacturers requirements.

[Lon Henderson]

Can someone show me any installation manual or code that drawing combustion air from a garage is allowed?

[Rich Goeken]

What the Flip Wilson are you talking about.
I was responding to post #3. But apparently that was not included. There have been some data base issues today.

[Greg Madden]

Is there a code issue with punching a hole for the intake (from the garage to conditioned space) through what may be a firewall?

[Scott Patterson]

Is there a code issue with punching a hole for the intake (from the garage to conditioned space) through what may be a firewall?

Sure, it just needs to be properly sealed. In my area the "Red" or "Orange" spray fireproof foam is allowed by the AHJ's.

[Jerry Peck]

Is there a code issue with punching a hole for the intake (from the garage to conditioned space) through what may be a firewall?

In addition to what Scott said, the duct needs to be minimum 26 ga, sealed, continuous to the furnace, seal to the furnace, and otherwise installed and sealed such that the combustion air duct does not provide or create any opening between the garage and the house.

[Rod Butler]

Can someone show me any installation manual or code that drawing combustion air from a garage is allowed?

I know you asked for a manual and I don't have one handy but I am going to respond anyway. The logic I would use is that if you can have a water heater in the garage why couldn't you have a furnace? As long as the combustion chamber is sealed from the supply air stream (you'd better hope that it is) then I can't see why there would be an exclusion.

- - - Updated - - -


Can someone show me any installation manual or code that drawing combustion air from a garage is allowed?

I know you asked for a manual and I don't have one handy but I am going to respond anyway. The logic I would use is that if you can have a water heater in the garage why couldn't you have a furnace? As long as the combustion chamber is sealed from the supply air stream (you'd better hope that it is) then I can't see why there would be an exclusion.

[Lon Henderson]

The logic I would use is that if you can have a water heater in the garage why couldn't you have a furnace? As long as the combustion chamber is sealed from the supply air stream (you'd better hope that it is) then I can't see why there would be an exclusion.


I thought of water heaters in garages too, and it makes sense that if the furnace flame is more than 18" above the garage floor or the unit is sealed, then there shouldn't be a problem, but I can't find anything actually saying that.

[Jerry Peck]

I thought of water heaters in garages too, and it makes sense that if the furnace flame is more than 18" above the garage floor or the unit is sealed, then there shouldn't be a problem, but I can't find anything actually saying that.

It's in the code .. "ignition source" is to be 18" above the garage floor.

"IGNITION SOURCE. A flame spark or hot surface capable of igniting flammable vapors or fumes. Such sources include appliance burners, burner ignitors and electrical switching devices. "

G2408.2 (305.3) Elevation of ignition source.
Equipment and appliances having an ignition source shall be elevated such that the source of ignition is not less than 18 inches (457 mm) above the floor in hazardous locations and public garages, private garages, repair garages, motor fuel-dispensing facilities and parking garages. For the purpose of this section, rooms or spaces that are not part of the living space of a dwelling unit and that communicate directly with a private garage through openings shall be considered to be part of the private garage.
- Exception: Elevation of the ignition source is not required for appliances that are listed as flammable vapor ignition resistant.

(while I am at it)
- G2408.2.1 (305.3.1) Installation in residential garages.
In residential garages where appliances are installed in a separate, enclosed space having access only from outside of the garage, such appliances shall be permitted to be installed at floor level, provided that the required combustion air is taken from the exterior of the garage.