Furnace Performance

[2010lexingtongts]

I recently bought a 2010 Lexington 255 GTS.  My home gas furnace kicks on and immediately starts throwing out warm then hot air.  In the RV , 55 degrees, with a 1/2 tank of propane, I get cool air for a few minutes, and then barely warmer air but never like at home.  Takes 2 hours to go from 55 to upper 60s with thermostat (analog) set at 80.  Is this normal for a RV furnace?  I can run all three stove burners at once with good flames on all 3.

[wolfe10]

2010lexingtongts,

Welcome to the FMCA Forum.

Yes, there will be a delay between thermostat signaling the furnace to turn on and gas valve opening/igniter sparking-- the PC board needs to see the SAIL SWITCH signal that there is sufficient air flow before initiating "fire". A few minutes sounds long, though.

Have you checked for ducts in the basement that may have come loose so the furnace is heating mostly the basement.

Assume you have stood outside and verified that the furnace exhaust IS hot.

[wildebill308]

46 minutes ago, 2010lexingtongts said:

I recently bought a 2010 Lexington 255 GTS.  My home gas furnace kicks on and immediately starts throwing out warm then hot air.  In the RV , 55 degrees, with a 1/2 tank of propane, I get cool air for a few minutes, and then barely warmer air but never like at home.  Takes 2 hours to go from 55 to upper 60s with thermostat (analog) set at 80.  Is this normal for a RV furnace?  I can run all three stove burners at once with good flames on all 3.

Welcome to the FMCA Forum.

The "I get cool air for a few minutes" part is normal as Brett said it has to go through a purge cycle before it will light the burner. It should blow hot air after that. I would check the things Brett mentioned and make sure the vents/cold air return are open and not blocked and let us know what you find.

Bill

 

[dickandlois]

2010lexingtongts, Looked through the brochure for you coach and there is no mention of a furnace. Find that unusual.

They do list a 13.5 BTU Roof AC unit and a 15.5 roof AC unit with a heat pump as an option.

Wonder if you could post the Make and the model of the furnace installed in your coach? From the description of the startup cycle, it sure sounds like there is a Atwood or Suburban unit installed though.

This is a link to the brochure 

https://library.rvusa.com/brochure/lexington2010.pdf

Rich.

[wildebill308]

Rich, I can't find one listed either. However in the pictures there appears to be a cold air return under the refrigerator and a hot air duct under the oven. I would be calling Forest River for more information.

Nice looking coach 2010lexingtongts. One more thought, make sure your thermostat is on "gas heat".

 

Bill

[bm02tj]

You need to have the gas pressure checked and if 10 or 11 in WC then have taken apart and the orifice cleaned as bugs may have filled with mud 

[manholt]

Don't know where you live.  Mud daubers goes anywhere to build their nest...have not heard of anyone getting stung by them, about the size of a hornet!  I found a small nest in my bathroom in the coach  a few years ago and could not figure out how they got in/out, until about a week later, I'm taking my evening shower and one flew by me to the nest, then a couple left, they got in and out thru a small hole in the screen to the fan and then between the lid and side...later that evening I got rid of the nest, put a piece of duck tape on screen and later had screen replaced !  I also put a Maxxfan cover on!  So, whatever exhausts opening you have from fridge, heather outside, put a screen over it.

[BillAdams]

7 hours ago, 2010lexingtongts said:

I recently bought a 2010 Lexington 255 GTS.  My home gas furnace kicks on and immediately starts throwing out warm then hot air.  In the RV , 55 degrees, with a 1/2 tank of propane, I get cool air for a few minutes, and then barely warmer air but never like at home.  Takes 2 hours to go from 55 to upper 60s with thermostat (analog) set at 80.  Is this normal for a RV furnace?  I can run all three stove burners at once with good flames on all 3.

NO!  This is absolutely not normal.  Yes, you should get air only for a short period of time while the sail switch trips and verifies that air is circulating.  After that the burners kick in and you should get HOT air from the furnace ducts.  If the 255 GTS means it's a 25 foot coach then you should be warm and comfy in less than 10 minutes.

[2010lexingtongts]

Thanks for the feedback.  The RV is in storage in the Denver area (and was bought from a dealer used and supposedly from previously owned in Colorado Springs) so I don't have access to the owner's manual right now.  I looked the other day and I think it was Dometic, but the manual  was for many different sizes so I don't know the size now.  The outside vent does blow hot air exhaust.  Funny the owner's manual doesn't list a furnace but it does have one.  I'll get the gas pressure checked when I can as that would explain why the furnace is under performing but the stove tops work great.

[wildebill308]

I bet it is the air ducts, either blocked or kinked not letting the air to flow freely. 

Bill

[wolfe10]

10 minutes ago, WILDEBILL308 said:

I bet it is the air ducts, either blocked or kinked not letting the air to flow freely. 

Bill

Maybe, but if too many blocked, the SAIL SWITCH would not close and furnace would not try to ignite.  That is the fail-safe for insufficient air flow.

[abyrd]

I had a similar problem,  the over temperature device would shut the burner off and the fan would run until it cooled down enough for the over temperature to automatically reset.  After further investigation was determined the there was inadequate air flow thru the heat exchanger.  After reviewing the furnace installation instruction, I discovered that the factory installation did not provide the minimum required duct size.  I added an addition register and worked fine.

I purchased the DP used when it was a few years old didn't realize the problem until the first winter. 

Jim 

[wildebill308]

1 hour ago, wolfe10 said:

Maybe, but if too many blocked, the SAIL SWITCH would not close and furnace would not try to ignite.  That is the fail-safe for insufficient air flow.

Who knows with out better information we are just guessing. Could be the duck's are not connected. If the exhaust is blowing hot then it is going some ware maybe the basement or up behind the refrigerator.

Bill

[manholt]

If the owners manual don't show the heater, it could be that the previous owner, was in the process of installing one, when he/she got the marching order and had to put it up for sale!  Common denominator being Colorado Spring and the Air Force Academy!

[tbutler]

You have to remember that the furnace is heating not only the air but all the cold furniture and the walls and ceiling.  If the outside temperature is really cold and if the insulation in the coach is thin, you could be losing heat to the outside through the walls and ceiling.  All RV's are not insulated as a house is.  We have a 40 foot coach and one furnace.  It sometime takes 20 or 30 minutes to cycle off for that kind of temperature change then will run again shortly.  This may repeat for several hours until everything (walls, floors, stuff in cabinets, clothes in closets, etc.) has warmed We have good insulation and double pane windows except the windshield.  Do check the functioning of the furnace but don't expect home performance from an RV furnace.

[2010lexingtongts]

I opened the vent under the fridge and the vents are connected, but I couldn't get to where I could see the flame.  It definitely was heating but the question now is whether it is heating enough.  I saw no evidence of insect stuff.  It is a Suburban furnace but I still don't know the size.

[wolfe10]

Did you (carefully) feel the exhaust (outside the coach)?

[2010lexingtongts]

Yes, heat is coming out of the vent, but I don't know what "normal" is?

[abyrd]

The over temperature device on my Atwood is 190 F. After increasing the air flow by adding new register the temperature varied between 150 F to 170 F depending on the inlet air temperature.

 

Jim

[wildebill308]

It (the exhaust) would be hot enough to burn you if you touch it.

You probably won't see a flame unless there is a window to the heat exchanger.

Look and see if there are other heat vents and that air is coming out. Hopfualey hot air. 

Bill

[abyrd]

Bill you are correct, you will not be able to see any flame.

The combustion chamber is separate from heated air passage that circulates the heated air into the coach.

[dickandlois]

The Coach we bought has 2 furnaces. A 20,000 BTU and a 35,000 BTU.

      Living at the Northern Latitudes - that was a selling point. With high winds(Big lakes do not restrict them) Ice storms and some impressive snow storms and the loose of power> The Coach is our backup for lost power and extra sleeping space for those family gathering or a warm retreat for others cough with few options.  

Note, just found this in one of the newer HR owners manuals and I can not remember ever seeing it before.

NOTE: It is not advisable to use the furnace to heat the interior of the motorhome during transit. ? 

Find it interesting, because we have traveled in 10 deg. weather and 400 cubic feet of volume can get cold with only the engine cooling system as the heat source.

Rich. 

Additionally - made up a full sized insulating sheet of Mylar R-4 for the windshield and the entry door. Both have a single pane of glass. Makes a big difference. They do not take up much space when roiled up and very lite weight.