357MDOK furnace not keeping up

[skidoomatt]

Originally Posted by JayG7800

3 - It would be nice to find a way to remove the 90 degree straight bends where the flex ducts connect to the top of the square duct runs. Again, I'm pretty sure this device doesn't exist either. I'm no expert, but 3 - 4" ducts pushing air to the direct bottom of the square living room run cannot be efficient in any way.

I agree with this also....I think flow could be much improved here. I have been searching also for a wye or duct transition pieces to try and use here but have not had any luck either. I am just gonna try and modify it myself to have a smoother transition. As things are getting cold here in Michigan and my camping season is done, I'm not sure if I'm gonna tackle this year yet or wait until next year.

If you come up with something before me, please share as I'd be interested in seeing what you did.

[JayG7800]

Originally Posted by skidoomatt

As things are getting cold here in Michigan and my camping season is done, I'm not sure if I'm gonna tackle this year yet or wait until next year.

If you come up with something before me, please share as I'd be interested in seeing what you did.

Yes, I am located in Vermont and the camping season is well over here, as well. I'm trying to get the furnace to be acceptable for next spring.

I rerouted, stretched and significantly shortened the three duct runs to the living room / kitchen square duct this morning. The one thing I noticed is the aluminum plate with the three collars which is screwed down to the top of the box duct, had it's holes not lined up at all with the actual duct run. See the attached picture. I removed the aluminum plate and re-cut the holes in the square duct so they now properly line up, and also moved it more toward the center of the vent. Also, the side of the plate which is closest to the wall was not taped down, it was conveniently tucked under the wall. I cut it down so I could properly tape and seal that side, as well. Before closing back up, I picked up a sheet of aluminum in the duct section at Ace Hardware, and cut a 2 1/2" x 14" piece and put it into the back of the rectangular duct at a 45 degree angle and taped it in place so it *might* help push more air down the rectangular duct into the living area.

I also moved the 2" bathroom duct run from the left side of the furnace to the 2nd open position from the left - swapping it with one of the runs to the living room.

Right now, 30 minutes later, the main cabin temperature sensor is now up 9 degrees (66F) and the bedroom is now up to 79 degrees (way too hot haha). So regardless, this is a huge improvement over how it arrived from the factory.

I need to test it out again when it's a little colder and less sunny outside to see how it behaves without those two factors. It is now up to 51 degrees outside. When I tested yesterday in the low 40s, it took one hour for the temperature to go up 3 degrees.


Future things to look at:

- Swapping the bathroom run from the 2" reducer right at the furnace to a 4" duct and splitting it down to two runs - one to the bathroom, one to somewhere else easy to get to.

- Disconnecting duct to bedroom to see if the aluminum plate there lines up properly - guessing it does since the bedroom is way too warm.

[3532]

Good work guys. I haven’t had time to mess with ours. Prolly be next spring. I’m confident we will get it to work after reading what your improvements have done

[JayG7800]

Originally Posted by 3532

Good work guys. I haven’t had time to mess with ours. Prolly be next spring. I’m confident we will get it to work after reading what your improvements have done

Yeah, it seems the furnace and propane supply is fine - whomever decided to rush through these ducts on the 357MDOK's - and probably more models - is the culprit. I forgot to attach the "after" pic post-cleanup, so adding it here for reference.

[JayG7800]

So I did another heating test again this morning after the modifications. Things are certainly better, but still not perfect by any means. This test was performed with the bathroom heat vent open and the master bedroom heat vent mostly opened. The electric fireplace was turned off. Thermostat was set to 70 degrees.

Time | Living/Bedroom| Notes
7:00a | 37 / 37 |41 outdoors, overcast
7:11a | 39 / 43
7:22a | 42 / 49
7:30a | 45 / 52
7:53a | 50 / 58
8:00a | 51 / 60
8:32a | 56 / 67
8:40a | 58 / 68
8:50a | 60 / 69
9:00a | 62 / 71 | Outside temp 47, still overcast.
10:00a| 68 / 78

I got sidetracked so I did not capture when the living room hit 70 degrees, but it still took essentially 3 hours to get up to temperature. I'm kind of curious how this matches other people with similar sized 5th wheels (~42ft).

I think I may be done messing with this for the fall. For the spring, I think I may just buy a portable electric space heater to use for an extreme cold heat-up event like the above test, plus turn on the fireplace for that added 5000btu. I may also try and see if I can build a better transition piece for the airflow to the main living area duct. I feel that if I mounted the transition duct plate (the sheet metal with the 3 duct collars on it) 90 degrees to the bottom of the duct, the air would at least be pushing more straight down into the square duct. I'd the have to build a tapered enclosure to transition from the ~18" transition piece down to the 2"x24" rectangular duct. I still don't know if that would make a huge difference, and not sure how difficult it would be to build and then secure in place.

I was really hoping to see it get up to temperature in 60-90 minutes, but it just isn't happening as-is from low temperatures.

[billcf7]

Take your house down to 37 and see how long it takes to get to 70, I don't think you'll see much difference

[JayG7800]

Originally Posted by billcf7

Take your house down to 37 and see how long it takes to get to 70, I don't think you'll see much difference

Yup, very true. I feel the only time this would matter would be when setting up on a very cold day. I feel pretty confident with these numbers that the furnace can certainly keep up during normal camping weather.

My old 33' Puma TT, on the other hand, could heat up in half this time - then again, 10' shorter, less slides, and lower ceilings.

[3532]

Sure sucks to burn a lot of propane on these tests too!! I appreciate all the feedback and hope I can contribute to the cause at some point !

And I agree there is a lot of cubic feet in these campers to warm up. Having the electric fireplace sure helps if that’s an option camping , I wish the a/c units had heaters in them also !


Thanks guys

[skidoomatt]

Nice work! Thanks for sharing all the feedback! I agree 2-3 hours coming up from 37 doesn't seem too bad.

[JayG7800]

So, one other item I came across this weekend was the possibility of using a 4" HVAC duct fan - perhaps putting this just before the transition from flex duct to the box duct. I wonder if this would help give the living room that extra "push" when needed. Just passing along a sample link - there are a ton of different brands / types on Amazon: https://www.amazon.com/AC-Infinity-R...p/B07ZL6FDYG/r

[skidoomatt]

Just thinking out loud here....

I've found these oval to round 90 degree duct "boots" as they are called. My thought is that I could put two of these side by side (oval end would slip inside the rectangular floor duct) in the end of the rectangular floor duct where it stops just inside the basement area. Mine is only capped off with HVAC tape, so it would be easy to put these in. I'd attach with some screws and more HVAC tape to seal everything off. I would then make a new "adapter plate" like the one the three ducts attach to the top of the rectangular duct with now, but just for one of the three ducts as the other two would be attached to those elbows.

My thoughts here are two of the ducts would now be blowing directly into the rectangular floor duct and would hopefully help "pull" the air blowing out of the duct attached to the top of the rectangular floor duct. Or maybe that top one would disrupt the flow of the other two too much?

I was also thinking of changing the flex foil duct coming off the furnace with semi rigid ducts, thinking it would be less restrictive. I understand all this would require some straps to support this so it doesn't become disconnected during travels.

Below are pictures of the items I was thinking of using. What does everyone think of this? I know this may be hard to picture and I wanted to draw a fancy diagram but didn't have it in me to do so at the moment. (lol) I'm no HVAC guy by any means....just trying to figure out how to optimize this poorly designed system.

Let me know your thoughts....

[JayG7800]

Originally Posted by skidoomatt

I'm no HVAC guy by any means....just trying to figure out how to optimize this poorly designed system.

Let me know your thoughts....

I think you're on to something here. I have my camper all closed up for the winter at this point, but building off your idea, they also make straight boots like this: https://www.plumbersstock.com/swbs41...ight-boot.html

That would take the 90 degree bend out of the equation for 2 of them, I think? These are taller than the box duct I think - if I remember right it was something like 2"x24"? A piece of sheet metal could be laid down on top reducing the height from the boot to the box duct. Maybe put the third duct off to the side of the box duct with something like this: https://www.plumbersstock.com/swbe41...-end-boot.html

I'm no HVAC guy either, but the less turbulence, the better the airflow should be.

[skidoomatt]

Jay,

Yes I did see the straight boots, but nothing seemed to match the size of the floor duct (2"x14" I think) and I was trying to find something I could piece together somewhat easily as I don't currently have any sheet metals tools besides an old dull pair of tin snips. Maybe time for some new tools?

My camper is all closed up for the winter too but as I could not find any indoor storage that wasn't already full, mine will be sitting at my house for the winter...which isn't all bad, since it will give me the opportunity to tinker with little side projects like this.

[skidoomatt]

So a little follow up on what I did with my trailer this spring...sorry, totally forgot to post here.

I removed all three flex ducts from entering the top of the rectangular floor duct which feeds the mid bunk and rear living area. I purchased the 90 degree elbows I posted about and also bought a "T" section. I also bought some semi-rigid flex duct to replace the flimsy stuff.

First I capped off the 3 open holes in the floor duct. Then I opened up the end of that duct and fitted my two 90 degree elbows in it. Connected the new semi-rigid duct to one of the furnace outlets. Added the "T" to the other 90 degree elbow and then connected the semi-rigid duct from the "T" to the other two nearest outlets on the furnace. I moved my bathroom connection to the left side of the furnace and left the duct feeding the front bedroom in place and added a blank cover plate to the other outlet in the right side of the furnace where one of the the main floor ducts was originally connected to.

With everything loosely fit I did a test run with the furnace.....much better airflow out of the floor vents in the mid bunk and rear living area! Bathroom and front bedroom no noticeable change in airflow. The mid bunk could probably use a vent with a closable damper on it so that room wouldn't get too hot. The furnace ran perfect with no shutting down for an extended period of time. So with that I went and taped and screwed everything together.

Due to the timing of our trips this year and the weather, the furnace has gotten little use, but I feel better knowing it will function when needed due to my fix of the duct work for better airflow out of the furnace. And throughout our trips this year, nothing has loosened or come apart either....surprising considering the crappy roads we have here.

So, this is what worked for me...really wish Jayco would have put some more effort into the airflow design on these units as it's obvious the furnace was not happy with the OEM design.