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Old 02-05-2018, 11:02 PM   #1
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Can I run the furnace blower to recirculate air

Trying to keep my enclosed underbelly warm when running off electric heat.

Is there a way to run the fan for the floor ducts to recirculate air? When I set the thermostat to fan it goes through the ceiling vents.

Am I missing something or is there a simple modification? Ive been thinking about upgrading to a digital thermostat, the one I have is your standard slide type, non digital. So upgrading t-stat would be an option
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Old 02-05-2018, 11:20 PM   #2
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Originally Posted by quicky06 View Post
Trying to keep my enclosed underbelly warm when running off electric heat.

Is there a way to run the fan for the floor ducts to recirculate air? When I set the thermostat to fan it goes through the ceiling vents.

Am I missing something or is there a simple modification? Ive been thinking about upgrading to a digital thermostat, the one I have is your standard slide type, non digital. So upgrading t-stat would be an option
Since you have an old style slide thermostat I have to assume you are not talking about a heat pump system. No, your plug-in electric heater will not provide heat your underbelly of the trailer. Your Gas furnace may provide some radiant heat to help some but not much. Just your furnace fan will not work. Not enough heat.
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Old 02-05-2018, 11:41 PM   #3
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Since you have an old style slide thermostat I have to assume you are not talking about a heat pump system. No, your plug-in electric heater will not provide heat your underbelly of the trailer. Your Gas furnace may provide some radiant heat to help some but not much. Just your furnace fan will not work. Not enough heat.
IM not asking people If it will be enough heat, I'm asking if I am missing a setting to do it, or if there is a common modification to do it.

And I Don't use a plug in heater, The built in electric fireplace is enough to maintain temperature in the camper if it stays above 15-20 degrees, with the propane system as a backup

I had the suction hose for the water pump freeze between the tank and the pump and I need to try an prevent that until I can get the belly opened up to add heat tape or something
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Old 02-06-2018, 12:02 AM   #4
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I had the same idea as yours. Instead of a electric furnace I used a portable heat pump. I could not find a way to run just the furnace blower fan. The thermostat as wired only runs the A/C fan for air circulation. I am sure it can be done, but was more than I wanted to pursue. Good luck.
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Old 02-06-2018, 12:03 AM   #5
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Not sure which unit you have but on mine if I select the blower to manual (not au) then select heat the blower will run. Just set the thermostat to a low setting, maybe 55 or so, and the gas will not come on but the blower will.

You will get airflow from the furnace only. If you select “cool” then the ac blower sends air through the ceiling vents.
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Old 02-06-2018, 12:13 AM   #6
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The best retrofit is adding heat coils to your furnace. Then it will run in electric mode and heat the belly area.
I don’t have it but it looked like a great idea.
http://www.rvcomfortsystems.com/
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Old 02-06-2018, 01:26 PM   #7
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Originally Posted by quicky06 View Post
Trying to keep my enclosed underbelly warm when running off electric heat.

Is there a way to run the fan for the floor ducts to recirculate air? When I set the thermostat to fan it goes through the ceiling vents.

Am I missing something or is there a simple modification? Ive been thinking about upgrading to a digital thermostat, the one I have is your standard slide type, non digital. So upgrading t-stat would be an option
Try turning your fan from auto to on !!!
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Old 02-06-2018, 01:51 PM   #8
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Try turning your fan from auto to on !!!
I don’t believe the OP is attempting to run his ceiling A/C blower while his furnace is heating. I believe the OP wants his furnace blower to run without heat to blow electrically heated air under the floor. I don’t think (not as definitive as some forum guessers) this can be done with standard systems.
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Old 02-06-2018, 02:02 PM   #9
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For safety reasons, I do not think on the standard thermostats, that you can run the furnace fan without heat as the actual operation is controlled by the furnace control board. You may be able to to add a manual switch the run the furnace fan without the furnace firing, but even then you will be pumping 68-70 degree air into the belly vs the much warmer output from a running furnace. On a cold morning, it might work, but it it got really cold, I am not sure you will get enough heat to keep things from freezing. If you want to avoid using your propane heater, you may be able to add a duct to the belly and feed it from a separate forced air heater. Probably just easier to use propane unless you are not paying for electric and are paying for propane.
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Old 02-06-2018, 02:05 PM   #10
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Typically, you cannot run the blower on your gas heater by itself. If you know what you are doing, you could install a relay in the furnace to run the blower by itself.
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Old 02-06-2018, 02:09 PM   #11
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For safety reasons, I do not think on the standard thermostats, that you can run the furnace fan without heat as the actual operation is controlled by the furnace control board. You may be able to to add a manual switch the run the furnace fan without the furnace firing, but even then you will be pumping 68-70 degree air into the belly vs the much warmer output from a running furnace. On a cold morning, it might work, but it it got really cold, I am not sure you will get enough heat to keep things from freezing. If you want to avoid using your propane heater, you may be able to add a duct to the belly and feed it from a separate forced air heater. Probably just easier to use propane unless you are not paying for electric and are paying for propane.

That’s what I’m gathering is the thermostat just sends a heat signal to the furnace and the rest is controlled from
There. I’ll have to see if I can get to it to put a switch in.

And the not paying for electricity is why I want to do this. It’s the same price per day no matter the electrical usage. In addition it would be nice to circulate air when the furnace is being used but not commanded on to try and stop from having to overheat the camper.
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Old 02-06-2018, 02:34 PM   #12
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Can I run the furnace blower to recirculate air

Almost all RV furnaces run the fan for a few after the end of cycle. This is a safety feature to purge hot air and gasses. The fans can run separately. The control mechanism is a different issue. They use a logic board to control the burner and fan.
Short of wiring in a separate switch and bypassing the logic board I don’t know how it’s easily accomplished if you don’t have that function at the thermostat.
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Old 02-06-2018, 02:42 PM   #13
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I wouldn't run the blower on a switch assuming you would want the switch to be some distance from the furnace. Depending on the model of your furnace, the blower pulls 3 to 10 amps of current. If you send that current through additional wiring and a switch, you would reduce the voltage to the blower. I would use a DPST automotive type relay with a DC contact rating of at least 10 amps. The relay would be in the furnace to do the actual switching and you can mount your remote switch anywhere you could run the wires. I would wire the relays NC contacts in series with the 12 volt line to the furnace components and run the NO contact to the blower. That way, you remove all 12VDC power from furnace control board and only apply power to the blower.
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Old 02-06-2018, 02:45 PM   #14
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No, you are not missing a setting on your thermostat.
From the factory, R/V furnace fans are not designed to run separately.

With that said, I have done it (on an older unit) and so did forum member Old Coot.

I simply wired a 12v feed to the blower motor (via a fuse, switch & relay) that I could turn on at will. Worked perfectly. You may have to dissemble a couple panels & part of the plenum on the furnace to get to the blower wiring but it isn't rocket science. If you have a good knowledge of how the furnace operates it shouldn't be too difficult.
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Old 02-06-2018, 03:22 PM   #15
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No, you are not missing a setting on your thermostat.
From the factory, R/V furnace fans are not designed to run separately.

With that said, I have done it (on an older unit) and so did forum member Old Coot.

I simply wired a 12v feed to the blower motor (via a fuse, switch & relay) that I could turn on at will. Worked perfectly. You may have to dissemble a couple panels & part of the plenum on the furnace to get to the blower wiring but it isn't rocket science. If you have a good knowledge of how the furnace operates it shouldn't be too difficult.
Just went and pulled the access panel on the front of the furnace. They mount the burners on the interior side of the unit. So it looks like I will have to remove it from the trailer in order to get to the back of it to get to the wiring. ( it’s in a small compartment under my refer)

I’m not sure I want to do all that right now. I’m planning 3-4 days of maint. / modifications this spring/ summer and I may do it then but not right now.

It will have to be done with a relay and once I can get to the control board it will be quick and easy. I found a wiring diagram for the furnace in the owners manual that came with it.

It’s just to cold and on too steep of a grade to do anything right now.
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Old 02-06-2018, 03:35 PM   #16
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Don’t forget Flybob’s comments that it’s possible very little heat will go into the basement. Air will still blow out all your regular heat vents and only a small portion of “room temp.“ air will go in the hole.
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Old 02-06-2018, 03:37 PM   #17
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Don’t forget Flybob’s comments that it’s possible very little heat will go into the basement. Air will still blow out all your regular heat vents and only a small portion of “room temp.“ air will go in the hole.
Which is fine. If it’s cold enough to freeze this should also lower the temp in the trailer causing the propane to come on.

Even if I put in an override relay it will still be able to run the furnace when commanded on by the t stat
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Old 02-06-2018, 03:39 PM   #18
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Which is fine. If it’s cold enough to freeze this should also lower the temp in the trailer causing the propane to come on.

Even if I put in an override relay it will still be able to run the furnace when commanded on by the t stat
Got it. Proceed.
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Old 02-06-2018, 03:42 PM   #19
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I hope people are not taking me as an *******. I’m just after improvements. No matter how small they add up. Eventually I’ll have duct vent pointed at he fresh water tank, and heat pads on everything. But doing this is my only help when I’m running off of batteries as I can run all my 12v appliances and lights for 20 plus hours before the batteries reach 50 percent.
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Old 02-06-2018, 04:17 PM   #20
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I don't think anyone is discounting what you want to do at all, just pointing out some of the pros & cons.

When I did it, it wasn't for moving warm air but rather cool/cold air.

At the time, I had a trailer that had a single A/C unit that wasn't ducted but my furnace was ducted in the floor. (go figure) I used the furnace fan to distribute the cool air (cold air falls) throughout the trailer. Worked great!
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