Hello All,Starting to prepare for my first winter in my trailer and have been thinking about heating. I am full timing right now and would like to use electric as my primary heat source to save my propane. I have a heated underbelly that is warmed by the furnace. What I have been thinking is that if I can use the furnace in a fan only mode to circulate the heated air created by my electric heater this should transfer heat to the underbelly without using the propane.What do you think? Anyone made a mod to their furnace to use the fan only?Thanks for your feedback.Terry

Yes, that would work, but there is another option and that is to add to your gas furnace.Check out this product CHEAP HEAT

You would have to run another 12V DC power source to furnace fan motor and switch the existing power source off because furnace fan only runs when t-stat calls for heat...which also causes the gas valve to open, spark electrode to light main flame etc.And your electric heater would not put out enough HOT air to sufficiently heat the underbelly, tanks etc. Are you going to be stationary or traveling?Stationary......have a local propane company set up 100$ propane tankYou need the propane furnace as primary and electric heaters as secondary....unless you decide to install the electric heater modification to your existing furnace discharge plenum.Heat source has to be at plenum in order to blow HOT air thru out rig.

Traver8 wrote:Hello All,Starting to prepare for my first winter in my trailer and have been thinking about heating. I am full timing right now and would like to use electric as my primary heat source to save my propane. I have a heated underbelly that is warmed by the furnace. What I have been thinking is that if I can use the furnace in a fan only mode to circulate the heated air created by my electric heater this should transfer heat to the underbelly without using the propane.What do you think? Anyone made a mod to their furnace to use the fan only?Thanks for your feedback.TerryThe amount of heat that this mod would put into the underbelly is so slight as to make it a waste of time and effort.Your propane furnace puts HOT air into the underbelly... Your proposed mod would put ROOM temperature air into it.Even most heated underbellys don't work as well as many imagine.Mostly because the insulation is lacking. I have never seen a TT that addressed the frame rail heat sink issue. Two steel I beams running the length of the TT uninsulated and conducting cold into the underbelly.After my experience of near zero temps I January, I found the limitations of my TT.I totally disassembled my underbelly,and put heat tape on ALL waterlines with insulation, improved the heat vents going into it, and super insulated the underbelly, including the frame rails.This January will be the test, as to just how effective all this was... I am sure it will be quite a improvement.

Huntindog wrote:Traver8 wrote:Hello All,Starting to prepare for my first winter in my trailer and have been thinking about heating. I am full timing right now and would like to use electric as my primary heat source to save my propane. I have a heated underbelly that is warmed by the furnace. What I have been thinking is that if I can use the furnace in a fan only mode to circulate the heated air created by my electric heater this should transfer heat to the underbelly without using the propane.What do you think? Anyone made a mod to their furnace to use the fan only?Thanks for your feedback.TerryThe amount of heat that this mod would put into the underbelly is so slight as to make it a waste of time and effort.Your propane furnace puts HOT air into the underbelly... Your proposed mod would put ROOM temperature air into it.Even most heated underbellys don't work as well as many imagine.Mostly because the insulation is lacking. I have never seen a TT that addressed the frame rail heat sink issue. Two steel I beams running the length of the TT uninsulated and conducting cold into the underbelly.After my experience of near zero temps I January, I found the limitations of my TT.I totally disassembled my underbelly,and put heat tape on ALL waterlines with insulation, improved the heat vents going into it, and super insulated the underbelly, including the frame rails.This January will be the test, as to just how effective all this was... I am sure it will be quite a improvement.Based on actual measurements of the temps inside my enclosed underbelly over the last 4 years in temps down into the 20's I think you would be surprised just how warm the underbelly is just from the natural radiate heat from the floor into the enclosed underbelly w/o any supplemental heat from the furnace. The temps I have measured are between 10 and 15 deg above the outside ambient temps. Now I do have some extra insulation in my underbelly over about 2/3 of the area between the frame rails. My remote sensor probe is about 6" from the frame rail and about 3" down from the floor. This 10 to 15 deg delta observation has been for ambients down into the upper 20's so in really cold and windy conditions I can't say what the temp would be, but the spread actually gets larger the lower the outside ambient temp. With zero heat from the furnace ducts my WAG would be nothing would freeze down to ambients in the high teens to low 20's. If you could just circulate the temp inside the trailer thru the existing furnace ducting you might keep the underbelly temp above freezing for temps down into the single digits.I think if I were to want to camp in really cold weather and use electric heat as much as possible I would cut like a 2 or 4 inch hole in the floor at the area around the waste tank plumbing and valves and around the FW tank and lines and run some duct to the inside of the trailer and mount one of the small computer fans in the duct to take the air from inside the trailer and direct it into the underbelly. Potential locations for these vents could be under or near the tub base or bath lower cabinet and around the area of the water pump. Of course all this would be highly dependent on exactly how the lines run in the underbelly and where the tanks are located.Larry

there was just a very good discussion on cold weather thing, with some of the same contributors. It would be worth your while to read it for some good info on preventing freezeups.

Furnace Fan Only Mode? | Good Sam Community

Gdetrailer
Explorer III
Nov 21, 2013
wrvond wrote:
Gdetrailer wrote:

Rigging the furnace fan could be done, basically would need to add a 12V SPDT (Single Pole Double Throw) relay in between the fan motor and the control board. The relay basically selects between the control board or direct 12V to the fan motor. Then a simple toggle switch can be used to turn the relay on for bypass.

Completely unnecessary if your thermostat has a 'fan only' position.

:R

Boy, you REALLY showed me...

Umm.. IF the OP of this thread HAD that SAME systems and T-Stat, they WOULD NOT HAVE POSTED their question in this thread in the first place.

In the second place, for your information, the MAJORITY of RVs DO NOT USE the type of T-stat you posted. That system COSTS MORE so most manufacturers opt for the SIMPLER HEAT ONLY T-Stat which does not have a fan only option or A/C control.

Besides even with the T-Stat you posted, it DOES NOT TURN ON the furnace fan (which IS what the OP is asking about). It only turns on the AC FAN. While one could simply turn on the A/C to fan only and circulate the air that way, it doesn't address the OP's concerns of getting heat to the HOLDING TANKS while not running the propane furnace.

I will stand by my original post on how to make the change AND as to why I know that it is not a good idea to make this change.
LarryJM
Explorer II
Nov 21, 2013
Old-Biscuit wrote:
That only controls the Cooling blower (A/C FAN)........

The furnace blower only operates when HEAT is selected.
Furnace blower only runs when furnace is operating.

Now you can run the furnace and have the A/C fan running (without compressor---cooling) to help circulate the air inside RV

Yep, however I have found like another poster mentioned if you put your electric heater in the area of the A/C and then run just the A/C fan on low that helps distribute the heat a little better through out the trailer sort of like using a fan to distribute the heat around when using an electric heater.

Larry
Old-Biscuit
Explorer III
Nov 21, 2013
That only controls the Cooling blower (A/C FAN)........

The furnace blower only operates when HEAT is selected.
Furnace blower only runs when furnace is operating.

Now you can run the furnace and have the A/C fan running (without compressor---cooling) to help circulate the air inside RV
wrvond
Explorer II
Nov 21, 2013
Gdetrailer wrote:

Rigging the furnace fan could be done, basically would need to add a 12V SPDT (Single Pole Double Throw) relay in between the fan motor and the control board. The relay basically selects between the control board or direct 12V to the fan motor. Then a simple toggle switch can be used to turn the relay on for bypass.

Completely unnecessary if your thermostat has a 'fan only' position.
Huntindog
Explorer
Nov 21, 2013
Gdetrailer wrote:
Traver8 wrote:
Hello All,

Starting to prepare for my first winter in my trailer and have been thinking about heating. I am full timing right now and would like to use electric as my primary heat source to save my propane. I have a heated underbelly that is warmed by the furnace.

What I have been thinking is that if I can use the furnace in a fan only mode to circulate the heated air created by my electric heater this should transfer heat to the underbelly without using the propane.

What do you think? Anyone made a mod to their furnace to use the fan only?

Thanks for your feedback.

Terry

Rigging the furnace fan could be done, basically would need to add a 12V SPDT (Single Pole Double Throw) relay in between the fan motor and the control board. The relay basically selects between the control board or direct 12V to the fan motor. Then a simple toggle switch can be used to turn the relay on for bypass.

HOWEVER running the fan by it's self is going to waste your heat. The reason for this is the furnace fan motor does double duty, it not only blows the inside air across the heat exchanger, it ALSO drives a fan on the burner chamber. This means the burner chamber is going to have COLD, COLD outside air being drawn into the burner chamber and PUSHED through the BURNER SIDE of the heat exchanger.

This will CHILL the heat exchanger and the inside air drawn across it will be cooled. Added to this you will be drawing warmer inside air (which in a RV is very humid) and condensing the moisture on the cold heat exchanger. This is going to cause a lot of rust to form on the heat exchanger.

Honestly, I really don't understand why folks who camp in the winter seem to be extremely cheap. SPEND the money on propane and use your furnace the way it was designed...

Excellent points! I have had my furnace apart, and that is exactly how it works... I had not thought it through as far as you did for this question...
Not only won't this idea work well,,, it will make it worse as well as being bad for the furnace.
LarryJM
Explorer II
Nov 20, 2013
Huntindog wrote:
It all depends on just how cold it gets. My first two TTs did not have enclosed underbellys. They were good into the teens.
This last one with a heated enclosed underbelly with factory insulation gave up at about 6 degrees.
Of course every TT is different but, I do not believe that putting room temp. air down there will do much more that make the TT colder inside.
BTUs are BTUs, and a electric heater doesn't have nearly as much as the TT furnace... And BTUs are the most important factor.

My point was there are what I believe over concern over using electric heat with it's lack of heating the underbelly and that concern for the most part is misplaced. As long as you are using say a max of 2 1500W heaters to heat your trailer just the radiate heat might be all that is needed to keep the underbelly area above freezing. If you can't keep the inside of the trailer at 70 deg with electric heat then that is probably still above the crossover point where temps in the underbelly will become a real concern.

As I mentioned it is extremely easy to stick a temp probe down say the hole in the floor for like the water pump and actually measure what is going on instead of simply guessing and speculating w/o any factsa which is IMO what about 99% of these posts about only using electric heat and underbelly temp concerns.

Larry
jimw606
Explorer
Nov 20, 2013
I installes a dedicated wall plug and circuit in my old Fver. Ran a heavy extenion cord and had an electric heater anytime I needed it. Worked vey well.
Gdetrailer
Explorer III
Nov 20, 2013
Traver8 wrote:
Hello All,

Starting to prepare for my first winter in my trailer and have been thinking about heating. I am full timing right now and would like to use electric as my primary heat source to save my propane. I have a heated underbelly that is warmed by the furnace.

What I have been thinking is that if I can use the furnace in a fan only mode to circulate the heated air created by my electric heater this should transfer heat to the underbelly without using the propane.

What do you think? Anyone made a mod to their furnace to use the fan only?

Thanks for your feedback.

Terry

Rigging the furnace fan could be done, basically would need to add a 12V SPDT (Single Pole Double Throw) relay in between the fan motor and the control board. The relay basically selects between the control board or direct 12V to the fan motor. Then a simple toggle switch can be used to turn the relay on for bypass.

HOWEVER running the fan by it's self is going to waste your heat. The reason for this is the furnace fan motor does double duty, it not only blows the inside air across the heat exchanger, it ALSO drives a fan on the burner chamber. This means the burner chamber is going to have COLD, COLD outside air being drawn into the burner chamber and PUSHED through the BURNER SIDE of the heat exchanger.

This will CHILL the heat exchanger and the inside air drawn across it will be cooled. Added to this you will be drawing warmer inside air (which in a RV is very humid) and condensing the moisture on the cold heat exchanger. This is going to cause a lot of rust to form on the heat exchanger.

Honestly, I really don't understand why folks who camp in the winter seem to be extremely cheap. SPEND the money on propane and use your furnace the way it was designed...
VAfan
Explorer
Nov 20, 2013
I use a 1500 watt electric heater and the AC fan on low….along with the furnace. Worked great for our fall camping – down to the upper 20’s at night.
ReferDog
Explorer
Nov 20, 2013
You can purchase 12V tank heater, in a blanket type, they have a self regulator that measures Out side air temp might give it a thought last trailer I owned had that system .

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