Ask Dave: Why is there no airflow from one of my RV’s furnace vents?

Dear Dave,
How can I get to the vent piping to find out why one of the three heat vents isn’t
putting out heat? The other two are putting out plenty. I’ve taken the cover off, but
can’t see anything. —Cynthia, 2012 Thor Four Winds

Dear Cynthia,
You did not provide a model, so I am not sure if your Four Winds is a Class C or a Class A. However, it looks like both models use the corrugated hoses to the vents rather than a metal plenum. [From Merriam-Webster: plenum: an air-filled space in a structure, especially one that receives air from a blower for distribution (as in a ventilation system).]

You should be able to locate the furnace by looking at the outside of the rig where you would see an intake and exhaust vent. In some of the photos I found on the internet it looked like the furnace was covered up by cabinetry and most often the lower drawers. You should be able to pull out the drawers or open cabinetry and have access to the furnace. You might need to remove a frame box or wall. There were times I have even had to remove the false floor of a wardrobe!

Check the furnace knockouts

The furnace has knockouts. Since you indicated two vents have airflow and the third does not, there should be three holes knocked out of the side of the burner assembly. As I’ve said many times, I never say “always” when it comes to RVs; so there might only be two knockouts and a “T” in one of the hoses. I would first take a look at all the hose connections, as typically low or no airflow is caused by a hose disconnecting from the burner assembly.

If all the hoses are connected properly, follow the hose that is going to the vent with no airflow and look for a collapsed hose, bend, or kink in the hose. Another issue could be the connection of the hose at the vent. From the photos I have found online, the vents are round and typically found in lower cabinetry such as kitchen, dinette, and even the bed pedestal. This means the ducted hose has to run through cabinetry and even sometimes down in the basement.

Try an endoscope to search for the issue

If you do not have access to see all the hose, I would use an endoscope and start from the vent inside the rig and fish it as far as possible. It might be a little challenging as the ribs of the hose will not make a smooth path for the camera end. You can find an inexpensive endoscope on Amazon here. There are also units that have a hand-held monitor so you don’t have to use a phone.

Another tool that may be handy is a fiberglass “fish” that will hold the camera end up slightly, which makes it easier to push the camera in further. You can find them on Amazon here.

 You might also enjoy this from Dave 

No airflow to RV’s bedroom heat vent. How do I see what’s wrong?

Dear Dave,
We think there are two issues that need to be addressed. But first, there is no airflow to our RV’s bedroom heat vent. Can we open the underbelly cover to see the plumbing and duct system? It appears sealed, but there are larger bolts. —John, 2021 Crossroads Hampton 380RKS

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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