Why no continuous furnace fan option?

[Williebago]

I am on my second 35 foot gasoline powered Class A coach and both have two roof mounted Dometic heat pumps and a separate gas furnace, one an Atwood and the other a Suburban. The heat pumps have high/low/auto fan positions, but the furnace only has an auto position. Why is this?

My stick and brick house furnace has a continuous fan setting. It would be nice when it was really cold to have this option so the furnace could supply some warm air to protect the water tanks and piping in the basement, whether driving or parked and plugged in.

[hohenwald48]

I installed a switch that allows me to turn on the furnace fan constantly if I want. It involved some splicing and wiring inside the furnace unit. I only use it to keep the basement above freezing when necessary. It's a pretty simple mod if you can read an electrical schematic.

[sundancer268]

I run my Suburban Furnace going down the road anytime I am cold. The dash system will not supply enough heat to keep us warm. Though I have found out that if the furnace flame goes out, the fan will keep running blowing cold air, so maybe you could just shut off the propane and start the furnace, the flame will not light and the furnace will go into the fault mode and the fan should keep running. At that point you can turn your propane back on and the furnace will not start up though the fan will still be running. When you get to where you need the furnace and the propane is on, just shut off the furnace at the thermostat for a minute or so until the fan quits running and then turn the furnace back on. I found this out when we woke up freezing one morning where the furnace had gone out during the night and the fan had not shut off, it was just blowing cold air. I pulled the furnace fuse and then restored power and the furnace took right off and started supplying heat. I later discovered all I had to do was shut it off at the thermostat and it would restart when the thermostat was turned back on.

[Heisenberg]

Mine heats everything back to the waterheater from the engine coolant via a switch on the dash. While travelling.

[dodge_guy]

Not sure about anyone else, but I don't want to hear the furnace fan running 24/7!

[doxiemom11]

We have been in some pretty cold temps where it did not go above freezing in the day and for several days in a row. With the furnace set at 60 at night and 68 during the day, no problem with the tanks. I don't think they need continuous heat to keep from freezing unless you are in the minus temps, then maybe.

[Williebago]

I have three remote thermometers at key locations in the basement around water piping and in the wet bay. When driving down the road in my gas coach, the basement thermometers indicate temps about 10 degrees above the outdoor ambient. So when driving below 20 degrees outside, it would be nice to have the furnace fan pump cabin air into the basement to protect things.

I recognize the furnace fan is a real drain on the batteries, but that would not be a problem if parked and plugged in or while driving with the engine alternator doing the charging.

On a side note, the furnace manual says do not run the furnace while driving.

[dougrainer]

I have only seen one of these and they are usually in hi line 5th wheels. Doug


https://www.camperpartsworld.com/RV-Atwood-Furnace-Excalibur-xt-25000-40000-BTU.html

[time2roll]

The furnace runs and cycles independently on its own controls. Thermostat just says go or stop.

This is different than the A/C unit that can be controlled with thermostat selections. At home the central AC and Heater are the same unit so again they can be controlled by the thermostat selection for fan.

[RoyF]

To address your concern about pipes freezing in the basement, why not get an external thermometer to put in your basement. Then you can keep tabs on how the basement temperature compares with the temperature outside.

If there really is a danger of freezing in the basement, you could allways use an (old style) light bulb near the pipes.

[DrewE]

Another reason why there is no continuous fan setting for RV furnaces is that the fan motor serves two purposes (there are two fans connected to the motor shaft). One fan is the circulator fan for the heated air, running on the house side of the heat exchanger. The other fan moves combustion air through the burner and heat exchanger on the other (outside) part of the heat exchanger. If there is no flame, the heat exchanger is going to be taking heat from the interior air and transferring it to the colder outside air. You'd be cooling the RV, not just circulating the air.

Household furnaces either don't have a fan on the burner side, relying on convection, or else have a completely separate blower assembly that can be controlled independently.

[Johno02]

Understand your problem exactly, and the other reasons are all correct. We use two small Vornado fans, one on the doghouse in front, and one in the back bedroom blowing to the front. We have found that these make a lot of difference in keeping temps more even all over the coach. And it's a cheap solution.

[Sam_Spade]

Williebago wrote:
but the furnace only has an auto position. Why is this?

Under what conditions are you likely to use the gas furnace ?
When you don't have access to shore power and don't want to run the generator all night, maybe ??

The gas furnace is there mostly for use when on battery power only.
Running the fan continuously would accomplish little to nothing BUT would sap the batteries rather quickly.

It is designed that way on purpose.

[dougrainer]

RV furnaces are designed to operate with a specific RPM. That is so the safety controls will function as designed. IF you had a continuous fan mode, that means the safety controls would have to be bypassed. COST is a factor. Home systems cost a lot more and the control systems cost a lot more. When you have that level of cost, the Home systems are designed to have continuous fan operation. Roof top RV AC/HP units do not have RPM needed safety systems. So, they can have whole RV fan operation. COST is the reason. Doug

[rockylarson]

The air flow from the fan moves the sail switch that tells the furnace that it is ok to release propane and start the igniter.
Not an expert but that is my simple understanding. Somehow I don't think having that safety feature open or not functioning is not advisable.