Furnace intake not outside.

I’m in training and inspected a house as one of my mock inspections today. The house had a newer furnace installed in 2004 and the exhaust vented outside through a PVC pipe, but I didn’t see an intake next to it? Is this acceptable? Shouldn’t the intake come from the outside?

It depends on the manufacturer. I always look up the installation instructions when I come across this. Even when the manufacturer says it ok, they generally recommend that the air from outside as a best practice. I put that in my report for informational purposes.

If the air comes from inside, combustion air requirements obviously apply.

In a lot of areas including mine the attic is considered as outside. Depends on your local AHJ.

That thread is just me and Bob going back and forth on the issue. I am sure there is a better one :slight_smile:

Is there adequate combustion air volume in the area of the furnace?

Appliances located in most basements, attics, etc get adequate combustion air from leaks in the building shell. Confined spaces can be a problem, however, if the home is airtight. There should be at least 50 cubic feet of volume in the room for every 1000 BTUs per hour of appliance input. Less than that, you want to recommend to either install an opening to another interior space or bring in the air from the outside.

I don’t even bother telling my clients this James. All I do is draw what is the best design because I have a HVAC background. Explain to them why it is better from outside and leave it at that.

Can you explain to me why the outside is better than a well ventilated attic???

Is that an acceptable practice ?
I’m in Florida and we don’t have many of these, if any .
So ! The question is genuine.

Yes, HE furnaces.

Hola checo a mucha sangría hoy ¿eh?
Enviarme una de esas havanas.

Me gusta un buen cigarro.

Safe to say lately you cannot find a thread without arguing back and forth between individuals but it still provides the basic information that it is acceptable by most manufacturers.

What is it ?

True, I just meant there has to be a thread with better inspectors arguing about it :slight_smile:

I wasn’t argung just asking;-) and I don’t consider my self better than the next dude

Charley I am speaking of our location where most furnaces are in the basement. Yes you would be correct for your area and I was not refering to attics.

Ok I can go with that nothing wrong with taking it outside but here we also have some basements and depending on SQ footage C air is allowed to be taken from the basement. C air reqirements should be determined by SQ footage and the BTU rating of the gas appliance not the location

Roy L., many High Efficiency furnaces use pvc to exhaust.

Like these:


Larry what is your take on recommending protection from possible summer nesting in the exhaust and supply vents?