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Open Roads Forum  >  Class A Motorhomes  >  General Topics

 > Why no continuous furnace fan option?

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Williebago

Wichita, KS, USA

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Posted: 11/19/19 10:13pm Link  |  Quote  |  Print  |  Notify Moderator

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.


WILLIEBAGO

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rk911

Wheaton IL

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Posted: 11/19/19 11:06pm Link  |  Quote  |  Print  |  Notify Moderator

we leave the fan on 24/7 at our home, too. don’t know but my guess is that our homes hold the heat better and longer than in our RVs. they cool down a lot faster and a running fan would just blow cold air.


Rich
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wa8yxm

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Posted: 11/20/19 05:07am Link  |  Quote  |  Print  |  Notify Moderator

THe fan burns 12 volt battery power. not 120 volt Mains power (though the converter does convert it) .. Frankly I do not know why no full time fan.

I do turn one AC on fan only for air circulation from time to time.


Home is where I park it.
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Argosy24

MI

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Posted: 11/20/19 05:39am Link  |  Quote  |  Print  |  Notify Moderator

A combination of the relatively small mass of the motor home cooling quickly, batteries dying even quicker, and a motor that isn't rated for continuous duty?

rockylarson

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Posted: 11/20/19 06:05am Link  |  Quote  |  Print  |  Notify Moderator

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.


Jan and Rocky
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dougrainer

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Posted: 11/20/19 06:20am Link  |  Quote  |  Print  |  Notify Moderator

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

Sam Spade

North Central Florida

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Posted: 11/20/19 06:48am Link  |  Quote  |  Print  |  Notify Moderator

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.


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Johno02

Lexington, TN USA

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Posted: 11/20/19 07:32am Link  |  Quote  |  Print  |  Notify Moderator

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.


Noel and Betty Johnson (and Harry)
2005 GulfStream Ultra Supreme, 1 Old grouch, 1 wonderful wife, and a grouchy, old, tiny dog


DrewE

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Posted: 11/20/19 07:54am Link  |  Quote  |  Print  |  Notify Moderator

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.





RoyF

Fayetteville Arkansas

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Posted: 11/20/19 09:31am Link  |  Quote  |  Print  |  Notify Moderator

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.

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