What's up with the Furnace Design?

[dewdev]

After reading these posts (and the link that Rivernerd provided), I have a few question and am looking for you-all opinions.

First - FYI, I do not plan to change the heater supply piping, at this point in time, as I only camp in the shoulder seasons (which can be somewhat cold in New England).

Second - I am thinking of adding a high and low return air vent to the closet as OTT has done in their newer models. Other than provide some ventilation to the closet, what benefit will those vents do to the overall cabin heating situation?

Third - I plan to add a return air vent low in the bathroom wall. Is adding a 4" round return air vent on the aisle side of the front dinette seat (return air to the same area as the bathroom vent provides) of any additional benefit to heating in the lower piping/tank areas and the cabin heat?

Thanks

[Chukarhunter]

I worry about Oliver owners with the Suburban furnace that close any heat vents (supply vents) in the trailer.  This is almost always detrimental to the functioning a an HVAC system but in the case of my generation of the LE II it can be dangerous.  According to my furnace manual, the furnace requires 25 square inches of unobstructed hot air venting to work properly.  Even a few feet of lightweight flex duct will restrict airflow and any bends in the flex duct will restrict airflow even more.  The two 4" round supply ducts in the Oliver total exactly 25 sq. inches at the furnace so technically, when the runs of flex duct are considered, Oliver has not ensured sufficient airflow for the furnace to operate at its best as it is.  (An analogy would be someone that exceeds the GVWR of their tow vehicle).  Closing one of the two cabin vents inevitably causes a sharp increase in back pressure against the furnace fan with the result that the fan cannot move as much air across the heat exchanger and into the cabin.  The result is hotter air coming out of the remaining open vent but less Btu's in total flowing into the cabin, and the likely overheating of the heat exchanger resulting in the furnace shutting down prematurely (short cycling).  In milder weather, this might not be noticeable but it is dangerous in colder weather because if the high temperature limit switch in the furnace ever fails, there is a serious risk of a fire.  The only safe way to increase the flow of hot air into the Oliver's cabin is to increase the number or size of return vents, which will reduce cabin pressurization when the furnace is running and thereby enable the furnace to move more air (and Btu's) through and out of the supply ducts.

In my experience, the key to comfort and balanced heating in the Oliver along with a warm bathroom is to ensure that all the hot air from the cabin must flow through the entire basement on its way back to the furnace, thereby heating the entire basement as well as the cabin. This requires additional return vents in the middle and front (bathroom) of the cabin.

[Rivernerd]

1 hour ago, Chukarhunter said:

In my experience, the key to comfort and balanced heating in the Oliver along with a warm bathroom is to ensure that all the hot air from the cabin must flow through the entire basement on its way back to the furnace, thereby heating the entire basement as well as the cabin. This requires additional return vents in the middle and front (bathroom) of the cabin.

I concur.  That is why I added 4" return air vents in the closet and under the front dinette seat. (Our Hull #1291 came with a return air vent in the bathroom.)

The return air vent under the front dinette seat is particularly important, because it channels more warm air through the "basement" of the street side of the trailer, and ultimately back to the furnace on the curb side.  This is important not only for furnace airflow balance, but to help keep the tanks and plumbing in the "basement" from freezing.

In my opinion, Oliver should install such return air vents in all new trailers.   It would add little to production costs, yet would make Olivers a much better "4-Season trailer," as Oliver aggressively advertises.

 

[Gliddenwoods]

Rivernerd

Please share what product, and source to purchase, you used to install new air return vents.

Thank-you

[Rivernerd]

11 hours ago, Gliddenwoods said:

Please share what product, and source to purchase, you used to install new air return vents.

I could not find the exact same product on the market today.  But, any 4" white round plastic vent cover will work, like this one available from Amazon for about $10:

https://www.amazon.com/Pack-Covers-Plastic-Protective-Ventilation/dp/B0822VXRNQ?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&smid=A2KUAC0DBLTG46&th=1

Good luck!

[Ronbrink]

On 1/22/2024 at 10:40 AM, Chukarhunter said:

My primary concern is the ability to keep the plumbing from freezing even when the cabin is warm.  I have placed internet connected thermometers in the basement by the outside shower hoses and other spots, and found that the basement temperatures can fall to 30 degrees or more below the cabin temperatures when outside air temps drop into the low 20's or teens. 

Just brainstorming here, but if one were to disconnect the duct hose from the aisle grille below the curbside bed and route it over to the outdoor shower components within the street side bed rear hatch, heat may then be sufficient enough in that area, and maybe even the basement, during extreme conditions. The abandoned grille could then be closed off to lessen concerns expressed by some, regarding short cycling of the heater due to that grille’s close proximity to the main furnace return, as well as too much heat at the rear of the cabin. As discussed, additional return vents fore at the bath and/or dinette seat, and aft at the street side bed area would improve air flow within the street side hatches and cabin areas. 

[rich.dev]

27 minutes ago, Ronbrink said:

Just brainstorming here, but if one were to disconnect the duct hose from the aisle grille below the curbside bed and route it over to the outdoor shower components within the street side bed rear hatch, heat may then be sufficient enough in that area, and maybe even the basement, during extreme conditions.

I was thinking of doing exactly that, then I saw the recommended duct lengths in the Truma manual (attached) just recently! It might still work, but I haven’t sat down yet to really mull it over! 

 

Truma furnace duct length.pdf.pdf

[Gliddenwoods]

1 hour ago, Rivernerd said:

I could not find the exact same product on the market today.  But, any 4" white round plastic vent cover will work, like this one available from Amazon for about $10:

https://www.amazon.com/Pack-Covers-Plastic-Protective-Ventilation/dp/B0822VXRNQ?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&smid=A2KUAC0DBLTG46&th=1

Good luck!

Thank-You

[Ronbrink]

15 minutes ago, rich.dev said:

I was thinking of doing exactly that, then I saw the recommended duct lengths in the Truma manual (attached) just recently! It might still work, but I haven’t sat down yet to really mull it over! 

 

I have the Dometic furnace in my 2020 OLEll. I can’t imagine an extended run length to the other side of the basement would exceed that of the distance to the bath. I didn’t look, but maybe the Truma manual is referencing total combined length limitations. It will be interesting to learn what’s determined when you “really mull it over”! 

[MAX Burner]

On 1/22/2024 at 2:31 PM, Steph and Dud B said:

That's what's we do. The first vent under the curb bed is closed.

Same here, works well and warm air trickles from the wet bath vent below the TP dispenser....FYI

[dewdev]

Today I added two 4" vents in the closet (one low and one high) in the same locations that OTT is installing in the newer Olivers.  Additionally, I added a 3" return air vent in the bathroom that vents into the underside of the forward dinette seat like OTT is now installing. I also added one 4" return air vent like Rivernerd recommended on the hall side of the forward dinette seat. I will be testing the heating system with these new vents later in the early spring,

The real reason that I am adding to the post is becasue I wanted to share where I purchased these vents. I looked on Amazon for 4" vents, like some have suggested, to get a price. I then called OTT and got a price for their vents. The price that OTT is charging is substanitally less than Amazon's price. I purchased from OTT 3-4" vents and 1-3" vent for about the same cost as Amazon was charging for one 4" vent.

IMO, for those with older Oliver's, that want to added return air vents, I recommend to purchase them from OTT and save youself some money. Plus my new vents now match what OTT is now installing.

 

[MAX Burner]

10 hours ago, dewdev said:

I recommend to purchase them from OTT and save youself some money. Plus my new vents now match what OTT is now installing.

Great post, @dewdev!  Thanks for sharing - we've got this mod listed on our spreadsheet as a priority...  I'll be calling Ryder this morning!  Thanks again!

[taylor.coyote]

Lots written about the furnace but everyone seems generally satified with its ability to warn the cabin living space. We have been in the Anza Borrego area (45-night / 75-day) and headed for colder weather. Even with modified ducting (hard elbows at furnace, hard straight runs passing through the water valve area and cutting 3.5' off in the bath vanity) our heater works hard to get the cabin temperature above 65 degree (starting at 55 degrees inside).  We find 65 comfortable but concerned about heating when it's 25 degrees outside. Is this normal?  please share your heating experience. 

Edited November 29 by taylor.coyote

[Geronimo John]

On 1/23/2024 at 11:48 AM, dewdev said:

I plan to add a return air vent low in the bathroom wall. Is adding a 4" round return air vent on the aisle side

My concern with this mod is that  humidity from showers will be vented to the basement.  That could be a problem in the cold areas of the basement in winter.  in summer it may be a source of moisture for growing mold/mildew.  Some have stated that such a vent would allow more air to flow into the bath area from the furnace.  I doubt this due to the poor quality and long duct run to it.  Frankly just keeping the bathroom door open when not in use will well ventilate the space with zero potental for unanticiated impacts below.

If you want to vent the curbside front basement, I suggest adding transfer vent in the front curbside seat base area.  Likely facint the CO/Propane detector.

GJ

Edited December 5 by Geronimo John

[Geronimo John]

These vents from Amazon.com matched our 2018 OE2 quite nicely.

GJ

 

 

[jd1923]

On 11/29/2025 at 11:03 AM, taylor.coyote said:

… our heater works hard to get the cabin temperature above 65 degree (starting at 55 degrees inside).  We find 65 comfortable but concerned about heating when it's 25 degrees outside. Is this normal?  please share your heatings experience.

Original owner replaced the Suburban furnace with an Atwood, so ours is somewhat different.

It works great, coming up to temp in a few minutes. So, if you set yours to 70F, will it not get there? We set ours at 64F overnight, comfortable sleeping temp, but I often bump it up to 68-70 in the evening when I feel cold.

I also did duct work. Removed the duct under the beds, removed the furnace outlet facing the rear, so that greater airflow would be in the proper direction. The air out of the kitchen duct is HOT to the touch and now we get decent heat to the bathroom.

Does the heated air at the kitchen duct feel HOT? Do you feel good heat outside at the exhaust? Hard to determine cause from afar…

Edited December 5 by jd1923

[taylor.coyote]

thanks for sharing. we sleep with the temp at 60F with no issues. The issue is if it's 40F outside, a cold trailer takes at least an hour to get to 65 and I don't think it can get to 70F.  The vent under the bed flows at 119 degrees, the kitchen at 99 degrees and the bath 72. We camped two nights ago at 20F. No problem to maintain the desired 60F while we sept but it topped out at 68F when we turned it up in the moring. I have read that 120 -140F is the temperature expected from an RV propane heater.  Our heater is adequate but at the bottom of what seems to be expected from an RV heater.

I would like to hear about other's heater experience / performance in cold weather. 

[Ronbrink]

20 hours ago, Geronimo John said:

My concern with this mod is that  humidity from showers will be vented to the basement.  That could be a problem in the cold areas of the basement in winter.  in summer it may be a source of moisture for growing mold/mildew.  Some have stated that such a vent would allow more air to flow into the bath area from the furnace.  I doubt this due to the poor quality and long duct run to it.  Frankly just keeping the bathroom door open when not in use will well ventilate the space with zero potental for unanticiated impacts below.

If you want to vent the curbside front basement, I suggest adding transfer vent in the front curbside seat base area.  Likely facint the CO/Propane detector.

GJ

I think it is important to run the vent fan when showering, as well as post showering for a while with the door closed, to remove as much moisture possible; even in cold weather conditions. While running with the door closed, the vent fan creates a negative pressure within the wet bath and draws heated air in through the vanity HVAC duct and any installed lower vent from within the under dinette area for that matter. Once the wet bath is completely dried, the vent fan can be turned off and door left open, whereby conditioned air entering the under dinette area via an installed lower vent is less likely to cause adverse effects and possibly improve return air ventilation. 

Edited December 5 by Ronbrink

[Geronimo John]

Totally agree.  I also keep the bath vent open  so as to create a chimney effect from the lower hull screened weeps and other sources.  Sort of an energy way to bring in a limited amount of fresh air.  Esspecially impotant to do so when using an open flame heate inside.  For that cracking a window is meeded as well.

GJ

[Rivernerd]

On 12/4/2025 at 5:56 PM, Geronimo John said:

My concern with this mod [adding return air vent to bath] is that  humidity from showers will be vented to the basement. 

Our Hull #1291 came with such a vent installed by Oliver.  I believe that venting was required by Truma when installing our Truma Varioheat furnace.

We have noted no moisture in the basement from the shower.  We run the bath exhaust fan when using the shower, and for 10-15 minutes thereafter, venting most of the shower-generated moisture outside.

Edited December 6 by Rivernerd
typo

[jd1923]

(Post deleted after noticing I was answering an old post.)

Edited December 6 by jd1923

[jd1923]

On 12/4/2025 at 9:36 PM, taylor.coyote said:

thanks for sharing. we sleep with the temp at 60F with no issues. The issue is if it's 40F outside, a cold trailer takes at least an hour to get to 65 and I don't think it can get to 70F.  The vent under the bed flows at 119 degrees, the kitchen at 99 degrees and the bath 72. We camped two nights ago at 20F. No problem to maintain the desired 60F while we sept but it topped out at 68F when we turned it up in the moring. I have read that 120 -140F is the temperature expected from an RV propane heater.  Our heater is adequate but at the bottom of what seems to be expected from an RV heater.

I would like to hear about other's heater experience / performance in cold weather. 

These are bad numbers, so I would conclude your furnace needs some sort of maintenance. An easy task is to remove the exterior panel and LP vent. Make sure all is clean and there are no flow obstructions. Fire it up for a minute with vent off and see if you can observe the burner in action for a clean blue flame. Check for any documented manufacturer's troubleshooting steps.

I say these are bad numbers in comparison to our Atwood furnace. We left camp for a long dinner with friends last night. Since we left our dog in the cabin alone, for safety reasons, I turned off the HWH and furnace and the LP at the tanks.

When we returned it was 57F in the cabin (outside was 49F and windy). I turned the thermostat up to 66F and although I did not time it, it seemed like 20 to 30 minutes max and the cabin was up to 65F. I do not have a proper instrument to measure air temp, but I placed a meat thermometer in the main duct. It started at 119F and stepped up to 172F! After I heard the gas shut off, the temp dropped back down at a similar rate.

I also have an infrared temp gun which measures surface temps. The inside of the duct measured in the 140s. Our furnace works better than new with ducting changes I've made, and given the numbers, yours seems to be in need service!

Hope this helps and please let us know what you find out! JD

[Snackchaser]

JD is right, your numbers seem too low.  This can be caused by several things.  Most frequently it's low gas pressure in the burner caused by  a restricted orfice jet clogged with debris.  If fan runs without heat then could be the Sail Switch sticking.  They can get corrosion on the pivot and need to be cleaned.  If the gas sounds like it's pulsing, and you hear clicking, then it could be a failing Limit Switch.  Then there is the flame sensor, looks like a thermocouple rod, they can get sooty from a poor flame.

Take a look and listen while the furnace running; you should hear the gas roaring with a good steady burn.  If it's weak or whistles then check the orfice.  Flame should be steady and strong, not yellow.  If it cycles about every minute-- with a burn then a click, then it's likely the limit switch.

There are videos for all of this.  I'd recommend shutting off the gas, opening the unit up from the outside, and just doing a thorough inspection and cleaning of things that you can easily access.  Then you can try it again and see how it works.

Stay warm and check out the Borrego Springs underground visitor center.  I helped build it about a half a century ago.

Cheers, Geoff

[Geronimo John]

7 hours ago, jd1923 said:

no flow obstructions

Mud Dobbers and Mice Nests have been seen before in furnaces.

GJ