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!