Poor Furnace Performance

[TLScout]

It is 45 degrees outside. I have a 2023 Cougar 23MLE fifth-wheel with a dometic propane furnace. The furnace is operating, but the temperature of the air coming out of the heat registers in the living space is much cooler than I would have expected—barely warmer than the ambient room temperature. The furnace has to run continuously to maintain 69 degrees inside. In my previous trailer (a Forest River bumper-pull with Suburban furnace) the furnace output was much better (warmer) and cycled on and off to maintain a consistent temperature in the coach. I noticed that the furnace in this trailer pulls its return air from the basement area and that I don’t have a direct cold-air return vent from the living space. My previous trailer pulled return air directly in from the living space.

Is my poor furnace performance normal for this fifth wheel trailer? I suspect it’s getting too much cold return air from the basement area and can’t bring that air up to a higher temperature to dump in the living area. I’m wondering if I would get improved furnace performance in the living space if I opened up and installed an air return in the pantry wall (which is near the furnace) to bring more pre-heated air into the furnace.

Has anyone done this? Any other thoughts or inputs before I start cutting a hole in my wall?

[dutchmensport]

Couple things going on here.

First, the return air flow back to your furnace from inside the living area of the coach is most likely, the vents located on the steps of your camper between the lower floor and the upper floor.

If those vents are covered, you will not have furnace air circulation inside the coach living aea.

Second, a great amount of heat is being blown under your floor. There are open ducts under your floor to help throw heat under there. It's designed this way to help keep your pipes from freezing. You can expect about 50% of the total heat generated from your furnace to blow under the floor. You will never fell or know this inside the coach.

Third. You are right in the fact the air under the floor is being pulled into the furnace. And you are right that is is cold air, even though some heat is being pumped under there too. What is happening is, cold air is being drawn from outside the underbelly of the camper. If you remove the back wall of your front pass-through storage area, and look inside that cavity, you'll be shocked at all the holes you see day light coming through. When the furnace kicks on, it's sucking cold air through every one of those holes, and yes .... making the furnace blow colder air.

What needs to be done first: make sure nothing is blocking the vents on those steps. Second, fill all those holes with putty, foamy insulation in a can (Stuff), and secure the underbelly Coloplast with more screws. Blocking all those holes will GREATLY improve the furnace's performance.

Sealing up all those holes will also keep those cold drafts away you feel on your feet when you walk on the lower level floor. Also, in the Summer, when the air conditioner runs, the air conditioner won't be sucking hot air from those same holes, pulling it through that vent in the steps and into the living are of the coach, making the air conditioner work harder, and appear to not get cool enough inside.

Closing up those holes will make a lot of difference on a lot a different levels in your camper. I plugged all of mine a few years ago. I used over 20 tubes of Liquid Nails and 10 cans of Foamy Insulation (Stuff). But the difference was remarkable when it was all finished.

[jsb5717]

45 degrees isn't that cold. The furnace should be able to cook you out...so something is definitely amiss. Our Dometic Furnace can keep us very comfortable with temps even in the teens.

If the furnace is working and blowing some heat (ie - as opposed to shutting off early after a brief ignition and blast of warmer air) then I'm not sure why it's underperforming. Hopefully one of the Chucks can speak into that.

As to the air return, I tightened ours up a lot. Now, our furnace heated us well from the start. But we were experiencing a lot of unwanted hot air blowing into the trailer from the underbelly during the hot months. I got behind the basement wall and sealed up every opening into the underbelly with spray foam. I also cut rigid foam to seal above the basement wall. Our air return is under our steps so I made sure that the only air that the furnace breathed came from the coach. That stopped the unwanted hot summer air and also improved the performance of the furnace.

Seems to me that your furnace should be heating your coach without doing anything. But having it breathe only air from the coach can only help it.

As to your air return, seems like you should have one. If you don't I'm hesitant to recommend cutting holes but it's a possible solution.

Oh, and Welcome Aboard! Thanks for joining. Let us know how this goes

[TLScout]

Originally Posted by dutchmensport

Couple things going on here.

First, the return air flow back to your furnace from inside the living area of the coach is most likely, the vents located on the steps of your camper between the lower floor and the upper floor.

If those vents are covered, you will not have furnace air circulation inside the coach living aea.
.

My floorplan does not have an air return in the steps. That’s why the first thing I thought I’d do was to create one either there or in my pantry which is closer to the furnace. I fully understand about all of the gaps and air leaks coming in through the underbelly. That will likely be my second thing to do. I’ll see benefits from that in many ways all year long (pests, cooling air loss, etc.). Thanks for the help.

[JRTJH]

I think I'd first make some "judgement calls" about the volume of air blowing out of the floor ducts in the trailer cabin. It almost sounds like the ducting is loose (or not even connected) at the furnace plenum. What it sounds like, to me, is that one or more of the ducts is disconnected and only minimal air pressure is being blown through those floor registers.

I'd check the furnace plenum to make sure all the ducts are properly connected, then start comparing the register output to try to identify any with significantly stronger or weaker air flow. That may give you some "hint" as to whether there are disconnected duct lines or even a torn or crushed duct in the underbelly.

It sounds to me like there is an "air distribution problem" not a "furnace hot air capacity problem".

[dutchmensport]

Well, this has me completely miffed then? If there is no return, then how in the world is the air circulating inside the coach? But, that could explain why the air flow is so bad too. There has to be circulation some how? surly?

[JRTJH]

Originally Posted by dutchmensport

Well, this has me completely miffed then? If there is no return, then how in the world is the air circulating inside the coach? But, that could explain why the air flow is so bad too. There has to be circulation some how? surly?

Like you, I'm not sure where his "return air" is coming from. Theoretically, if the belly is sealed, any air blown into the belly(say from a disconnected duct) could pressurize the entire underbelly and that "air pressure" could be what he feels coming out of the floor vents. That could explain why the temperature is so much colder at those vents. It's being "cooled in the basement" and only slightly warmer than ambient air by the time it makes its way to the back of the trailer to be forced up, into the cabin through an open floor vent.....

As you suggested, it "could be" a return air problem and the supply runs from the furnace to the floor vents are OK, or it could be that the return air is working properly and the issue is in the supply runs, from the furnace to the floor vents.

Unfortunately, to make troubleshooting even more difficult, there could be issues with both the return air drawing from the outside, unheated area AND problems with leaking/crushed/damaged ducting to the floor vents.

[jsb5717]

One thing the OP could try is to turn on all the lights inside the coach. Then open up the basement wall and see where light is coming from. It might reveal an air return.

[Roper46]

I just did a virtual tour of the 2023 Cougar 23MLE and there is definitely no return air in the steps, it is carpeted. I looked in the rear kitchen area and all along the floor in the living area and nothing. Then I looked upstairs and I cannot see what looks like a return air area.

But I would think there would have to be one for the living area somewhere.

[jasin1]

Originally Posted by TLScout

It is 45 degrees outside. I have a 2023 Cougar 23MLE fifth-wheel with a dometic propane furnace. The furnace is operating, but the temperature of the air coming out of the heat registers in the living space is much cooler than I would have expected—barely warmer than the ambient room temperature. The furnace has to run continuously to maintain 69 degrees inside. In my previous trailer (a Forest River bumper-pull with Suburban furnace) the furnace output was much better (warmer) and cycled on and off to maintain a consistent temperature in the coach. I noticed that the furnace in this trailer pulls its return air from the basement area and that I don’t have a direct cold-air return vent from the living space. My previous trailer pulled return air directly in from the living space.

Is my poor furnace performance normal for this fifth wheel trailer? I suspect it’s getting too much cold return air from the basement area and can’t bring that air up to a higher temperature to dump in the living area. I’m wondering if I would get improved furnace performance in the living space if I opened up and installed an air return in the pantry wall (which is near the furnace) to bring more pre-heated air into the furnace.

Has anyone done this? Any other thoughts or inputs before I start cutting a hole in my wall?

you say it’s running continuously? are you sure the fan isn’t set to “on” and is running all the time? when you do that the furnace burner will cycle off and on via the thermostat setting but the fan will never shut off….you will feel much cooler air if you check it between burner cycles….but it will blow 24/7

you said it’s maintaining 69 degrees so i’m thinking that’s the issue..or perceived issue

also look under the dinette seat storage area when you walk in the door…they may have moved the return over there so you don’t see all the wires and junk in the basement like you do when the grill is in the steps…or maybe one of or all of the floor grills is a return as well as a supply…it looks like they changed to plastic modern floor registers that may have openings around the perimeter directly into the basement ( unlikely though)

[sourdough]

Here's a link to a trailer walk through;

https://www.youtube.com/watch?v=6S4wpIVp9I4

At the 3:25 mark you can see the return air vents under the stairs. Your trailer does not have those? I looked at the Keystone 3D walk through but it does not let get where you can view them.

[jsb5717]

Originally Posted by sourdough

Here's a link to a trailer walk through;

At the 3:25 mark you can see the return air vents under the stairs. Your trailer does not have those? I looked at the Keystone 3D walk through but it does not let get where you can view them.

Well, that seems pretty clear. You'd think the OP wouldn't be able to miss those. So if his steps don't have those then...why?

If he was thinking about cutting some in that would be a good place.

[RollaMo]

Here is screen shot showing a 2023 23MLE with NO vents in the steps, just like the OP mentions his is like.

Did they make a change during the production run?

[jsb5717]

Hmmm...I just saw another walkthrough that looked like this. I'm guessing this is what the OP is talking about

[jasin1]

The pictures i posted on post 10 were screen shots of a walk thru…the only place i could see where its possibly located is under the dinette seat as you walk thru the door on the left…there were none shown in the steps

[jasin1]

Originally Posted by jsb5717

Hmmm...I just saw another walkthrough that looked like this. I'm guessing this is what the OP is talking about

lol this is what i posted above in post 10

[TLScout]

Originally Posted by JRTJH

It almost sounds like the ducting is loose (or not even connected) at the furnace plenum. What it sounds like, to me, is that one or more of the ducts is disconnected and only minimal air pressure is being blown through those floor registers.

I'd check the furnace plenum to make sure all the ducts are properly connected, then start comparing the register output to try to identify any with significantly stronger or weaker air flow.

Yes, I thought about that as well and best I can tell--all of the hoses are connected to the plenum. There was a little bit of air leaking from a few of the connections at the plenum so I sealed the leaking ones with some metal ducting tape. It might have helped a little, but not much. I'm getting decent flow at all of the registers--but it's just not up to the temperature it should be. I still think it is a problem getting good return air from the living area into the furnace to be re-heated. The only way return air can get back into the basement area and into the furnace is through cracks and seams.

[ChuckS]

Your furnace should be the Atwood AFM/DFM 35 series

BTU input is 35K
BTU output is 25K

Have you used a thermometer and measured the output air temp at each floor duct yet?

The further away from the furnace fhe duct is the cooler the air will be and the volume will be less

I would check the air duct from the furnace plenum to the floor duct for kinks, etc

The stairwell return ducts .. which your Floor plan doesn’t have don’t do squat for overall performance of airflow front the furnace.

My stairwell ducts have been blocked off for the ten years I have owned my unit .. at 0 degrees outside temp my furnace will run you out of the unit if you set the temp above 65 degrees..

I set our furnace at 55 to 58 degrees at night when in cold weather and it runs a few minutes here and there to maintain the set temp.

YMMV

[TLScout]

Originally Posted by jasin1

you say it’s running continuously? are you sure the fan isn’t set to “on” and is running all the time? when you do that the furnace burner will cycle off and on via the thermostat setting but the fan will never shut off….you will feel much cooler air if you check it between burner cycles….but it will blow 24/7

also look under the dinette seat storage area when you walk in the door…they may have moved the return over there so you don’t see all the wires and junk in the basement like you do when the grill is in the steps…( unlikely though)

Thanks for the suggestion about checking the fans--but I'm sure I have the HVAC fans set correctly. I've turned off all of the rooftop systems and fans and the only blower that is running continuously is the one for the furnace that circulates air through the floor vents and underbelly. I can lower the thermostat and the propane furnace will turn off as expected. I just can't get good warm air flow into the living space.


The exhaust from the furnace going outside is hot, so I know that the furnace is heating up the air exchange area--I just think its pulling cold air in from the underbelly rather than re-circulating air from the living space.

[TLScout]

Originally Posted by sourdough

Here's a link to a trailer walk through;

At the 3:25 mark you can see the return air vents under the stairs. Your trailer does not have those? I looked at the Keystone 3D walk through but it does not let get where you can view them.

Thanks for finding this video!! That is certainly my floorplan and rig--but I do NOT have the under-stair return air vent as shown in the video. I've looked throughout the coach and there is no return air vent in my camper. I'm starting to think that they "forgot" to install it. Right now--the only way that air gets back to the furnace from the living area is through gaps in the floor/walls and drain openings.