Cat 4 furnace verbiage

[William J. Decker]

Can anyone give some verbiage on this issue.

Rheem 2005 sealed combustion cat 4 furnace installed in an attic room. The combustion intake air vent was open to the attic, not taken outside.

Buyer talked to the village code people and theu said it was OK.

I was always informed that Cat 4 sealed furnaces should take their air from outside.

The attic room had 2 vents to the attic.

Comments to support my arguement?

[Charley L. Bottger]

Originally Posted by wdecker

Can anyone give some verbiage on this issue.

Rheem 2005 sealed combustion cat 4 furnace installed in an attic room. The combustion intake air vent was open to the attic, not taken outside.

Buyer talked to the village code people and theu said it was OK.

I was always informed that Cat 4 sealed furnaces should take their air from outside.

The attic room had 2 vents to the attic.

Comments to support my arguement?

Cannot support you Buddy they are not required exterior to the home in my area just inspected one this week made its turn right in the middle of the attic space. Would be a different story if the attic was sealed but with a vented attic what is the difference. We have been taking combustion air from attics on other furnaces for a hundred years why not this one.

[mthomas2]

If a CAT IV furnace has *both* a combustion vent pipe *and* a combustion air intake pipe, every installation instructions I've seen require that the termination of *both* pipes be in the same atmospheric pressure zone. If the combustion air intake pipe (connected directly to the furnace) terminates in the attic, and the combustion vent pipe is venting to the exterior, they are not. (Note that this is NOT the same as the same furnace drawing combustion air from a utility closet drawing combustion air from the attic.)

[Matt Berman, CMI]

There are some cat 4 furnace mfgr that allow you to pull combustion air from the surrounding space as long as it is not a confined space. York is one i can think of.Matt

[Matt Berman, CMI]

Read installation instructions,they should be at or near furnace area .Matt

[mthomas2]

For an example, see item 2 at the top of page 11 (document page number, shows up as page 17 in my Adobe reader) here:

http://www.thermopride.com/manuals/mg1010.pdf

An attic is not in the same "atmospheric pressure zone" as an exterior location as wind forces will often be produce pressure differences between the inside and outside of the attic. Again, note that this applies only to the situation where the furnace is drawing combustion air via direct connection to an intake pipe, not to an arrangement in which the furnace is drawing its combustion air from a utility closet with a properly sized connections to a vented attic.

[Charley L. Bottger]

Originally Posted by mberman

There are some cat 4 furnace mfgr that allow you to pull combustion air from the surrounding space as long as it is not a confined space. York is one i can think of.Matt

So Is American Standard

[William J. Decker]

Thanks, Mike.

Client is lawyer and the sellers are very defensive.

Never allow the local AHJ to determine what is right. They are (usually) less informed than the local HVAC guys. No CE requirements.

[Gary Reecher]

What do the furnace's installation instructions say? Though village codes say it may be alright if the installation instructions require a combustion air pipe outside of the structure then one will have to be installed.