Yesterday I posted a question from Cynthia regarding no airflow in one of her RV’s furnace vents. Today I received a response from her with several photos of the vent tubing and thought it would be a good follow-up for readers to see what might be the issue.
My RV is a 2012 Thor Four Winds 28Z. I was able to get into the furnace behind a grate below the fridge. There were two cutouts to my left, one to the right, and the front cut out just blew through the grate. There are four vents: one in the bedroom, one in the bathroom, one in the kitchen when slide is out, and the one at the top of the entry stairs that seems to come in from underneath the shower. —Cynthia
As I suspected, the vents are incorporated into the lower cabinetry and use corrugated tubing or hoses snakes in and around the furnishings.
Bent hose
At first glance I would say the hose on the right is severely bent and could be causing an airflow issue; however, it is not certain which vent this goes to. But what concerns me is the open hole in the middle. According to Cynthia, it just blows air straight out the hole thru the grated cover! If the hoses are bent like this and the photo below, the air could naturally blow straight out the hole rather than the other hoses.
Since this is a 2012 model, I wonder if the vent has ever worked or if this just started. Cynthia also stated that the vent in question is the one going to the top of the entry stairs, which seems to come from under the shower. Here is an example of the floorplan.
Hose may not be attached
With the furnace located underneath the refrigerator, the hose would need to come underneath the floor, come up under the shower, and make another 90 degree turn to attach to the vent shown in the photo. I would suspect it is either kinked or came loose. I would suggest removing it from the cabinet to see if the hose is attached.
I received this today from Cynthia.
Good morning, Dave,
To answer your questions, I don’t know whether it ever worked or not as the motorhome is new to us. We purchased it in December.
A LOT of warm air comes out of the front opening. It blows out through a grate below the refrigerator. The distance between the opening and the grate is only about 6 to 8 inches. There is another opening on the right side of the furnace box, too. That side is inches from a cupboard wall. Should I close these? If so, how?
The vent opening into the bedroom is putting out too much heat. I’m thinking I should replace that vent cover with one that is adjustable so that I can reduce that air flow.
FYI–This motorhome is a Class C.
I have an endoscope coming from Amazon tomorrow, but, thanks to your troubleshooting, I am guessing my issue is one of equalizing the flow through the hoses.
Cynthia,
The open cutout blowing air under the refrigerator is definitely taking the majority of airflow and limiting the other vents. The problem with closing off vents or even putting a damper on the grate under the refrigerator is limiting airflow back at the furnace and temperature, which would cause a shut off due to low airflow at the sail switch or high temps at the limit switch.
I would suggest checking out the vent that is not working and trace it back to the furnace to see if the hose is disconnected or bent. Then you will need to evaluate the other vents and how well they are distributing heat to the rig.
You might also enjoy this from Dave
What’s causing the RV furnace to run a short time and then show airflow-limit fault?
Dear Dave,
My daughter just purchased this fifth wheel. When we turn the heat on it runs for a while then triggers the airflow/limit fault. I don’t know what to look for as the cause. I was thinking a dirty filter, but I can’t find one. —Ricky, 2020 Coachmen Brookstone
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Thanks for the follow-up Dave.
What scumbag would put a physical obstruction in front of the heat vent opening or did they cut the hole in the wrong place. Looks like a door jam or some sort of support bar. What shoddy work and or lack of planning.
Fantastic troubleshooting, Dave! Even when the problem you solve isn’t one that I have encountered, your answers are always so helpful; sometimes applicable to other things in my RV. Thanks!
I’d be careful with the endoscope as the walls on the furnace tubing can be thin.
Thank you, Dave! I echo what volnavy007 said. 🙂 Safe travels! 🙂
It’s hard to tell from the pictures, but it appears that the opening in the cabinet is for the return air. Having the unconnected port there would cause the hot air to just return back into the furnace and limit the air flow.
I agree with Bob. The grill under the refrigerator is a cold air return. The open port should have a duct connected to it otherwise the hot air will just recirculate back into the furnace. There is either a missing duct hose or that opening should be blocked off. I would first count the number of outlets in the unit and see
if you have the same number of ducts on the furnace, that should tell you if there is a missing duct or you need to block off the opening.
I had this problem with a new Grand Design Reflection fifth wheel in 2017. There was no heat in the upstairs bedroom and it was cold out…so I went to work finding out why. Remember this was a new off the lot trailer and had went through the dealers supposedly pre-delivery inspection. After tearing out a wall in the basement I found a heater vent hose laying on the basement floor…never had been attached…so much for an inspection. I fixed it with screws and gorilla tape..no more heat problems. Just shows dealer inspections cannot be trusted.
Those 90 deg bends, especially with the flex-duct shown, are creating a lot of turbulence and subsequent back-pressure in the ducting. Inexcusable for that path of least resistance center port being left open with no duct at all! There appears to be no pre-planning on how to distribute heat in this unit. (The duct work is very thin – so be careful with the endoscope; if you feel resistance – stop pushing!).
There is no HVAC engineer on this design team. Sad.
Thank you Dave and Cynthia with regards to heating duct problems in a 28Z Class C motor home. I experience the same issue with regard to heat vent at top of steps. Pictures and comments will assist me to deal with this issue. For what it is worth we have very little in the way of problems with this MH. has been reliable & no major issues . A little TLC and minor maintenance has gone a long way. Installed a sliding drawer under the bench seat and also access to under side of sofa for footwear. These two modifications have been incorporated in some of the newer models.