In taking this course I wanted some input on the pictures of this warm-air, gas furnace. It has an inducer, type B vent. A fairly large area the furnace is in. However there are to two air-vents about 10 feet from the furnace that has a gas-vented water heater next to it. The vents connect to a finished area of the basement with a return. Would this not be going against the statement: “Never install a Category I furnace using the CAZ as the return air plenum; duct the return plenum to return registers in other parts of the house. The return air side of the forced air furnace should have no communication with the CAZ at all.”
What does “CAZ” mean, Robert?
I’m a little slow having been cooped up for for so long, and all.
Combustion appliance zone.
I think the cutouts for the grills, in the picture below, are for potential combustion air and not part of the return air system.
And, I don’t see how the vents are connected to the return air system.
They are not connected to the system. Bad choice of words. They communicate in this way: when the system is on the return will also pull air from the furnace room area because of these vents. There is also a gas water heater. Could this contribute to backdraft?
When what system is on?
Oh, you mean when the furnace is on.
Personally, I think there is way too much air available for that to happen.
But, alas, I suppose it could produce a negative draft but I find it hard to believe with what I see in the pics. JMHO…YMMV
I always perform a CAZ test when there are atmospheric drafted and non sealed combustion appliances. You don’t need a digital manometer but it helps fo define specific values at which point the appliances fail the test. The only way to know is to perform a CAZ test. The system in question is of poor design. Those vents should be blocked off into the mechanical room. If supplying heat to the room was the motivation for these vents then they should have just cut a register in the supply duct or plenum. Common practice is to bring two in combustion air ducts from the outside into the room. One high and one low. The only way to know is to test.
I once had a furnace and water heater in a small closet. No combustion air supplied. Tests were coming in at negative 10pa and I still couldn’t get the water heater to back draft. A few weeks ago I did a CAZ test on a laundry room with atmospheric gas water heater. Although I was only getting negative 3pa the water heater would not stop backdrafting with the dryer running.
I agree with Walter on this and the common practice of supplying combustion air being from outside with one high and one low. However, I don’t believe the reason for the vents was to heat the room.
So, a CAZ test it is…
The finished area has supply registers, do the vents are not for heating. Perhaps they are wanting to increase the area for combustion air.
That is what I was thinking when I looked at your pics.
And I see nothing wrong with what they did. Not how I would have done it but so what.
So my final question then is what is meant in the course material that: “The return air side of the forced air furnace should have no communication with the CAZ at all.”
And thank you, everyone, for your input!
One final note. There appears that there was an open duct that lead to outside. However, it has been terminated. The furnace is original to the home. See the photo, red rectangle.
IDK, Robert. Maybe the ten foot rule of no return air ducts within 10’ of the furnace.
Otherwise, you may want to ask Ben Gromicko regarding the wording and meaning.