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Old 01-13-2025, 08:49 PM   #1
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Generator with underpinning?

Hello everyone, got a new-to-me 2005 Montana 37' 5th wheel. Came with a propane powered Onan 5500 in the front compartment.

I'm setting up at a new property I'll be developing, so it will be there for a couple years while we are on the project. For the winter season, I'm considering underpinning the RV with insulated foam board. Another guy did this and it made a world of difference.

If I lost power and switch the Onan on, would this be ok with underpinning??

The exhaust runs out the side, and I am considering hooking it to an extended pipe to get it further from the RV.

But what about airflow, air intake, and overheating?

I think it would help to not underpin the whole front tongue, and just go across the front of the landing gear. This leaves the front compartment door exposed at least, even though the bottom of the bedroom floor won't be enclosed that way.

I'm guessing the generator takes in air from underneath though, so I'm wondering if this would cause issues.

Would be great to hear from someone that knows more about this.
Thanks!
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Old 01-13-2025, 09:28 PM   #2
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If the cooling air stays under the camper, it will make some warm floors! Should be fine to run intermittently, but not unsupervised.
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Old 01-13-2025, 09:29 PM   #3
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...... Came with a propane powered Onan 5500 in the front compartment.
.
.....
Thanks!
That size Onan is air cooled so do not block the air flow.

You do not need a tail pipe extension but you should make sure your CO detector works.
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Old 01-13-2025, 11:27 PM   #4
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That size Onan is air cooled so do not block the air flow.

You do not need a tail pipe extension but you should make sure your CO detector works.

Is its primary air flow from beneath? I don't really see where else it would draw air from, other than the void space underneath the propane bottles in the side compartments.

With all the space under the RV, and foam board not being completely airtight everywhere, I wondered if it would still have plenty of air flow?

I was also kind of curious if the compartment door is actually supposed to be swung open a little bit.
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Old 01-14-2025, 07:52 AM   #5
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Is its primary air flow from beneath? I don't really see where else it would draw air from, other than the void space underneath the propane bottles in the side compartments.

With all the space under the RV, and foam board not being completely airtight everywhere, I wondered if it would still have plenty of air flow?

I was also kind of curious if the compartment door is actually supposed to be swung open a little bit.
Look underneath the generator, the bottom of the generator on our 5th wheel is opened. It draws cooling air from there.

Sometimes I open the front door, especially when it is hot. When it gets above 100 deg., I sometimes place a cooling fan on it as well. But when the temps are low, I leave the compartment door closed.

On the inside of the front compartment door, the panel is a little warped from the high temps. So, that is why I open the door in higher temps when we need the generator operating.

If concerned with the foam board, leave the bottom of the generator opened, then box in around it.
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Old 01-14-2025, 10:03 AM   #6
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Start the generator and watch were the cooling air blows out. If it is underneath do not block that part of the belly.
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Old 01-14-2025, 06:20 PM   #7
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The underside of the front compartment on mine has no air inlet or holes, other than the small slot the oil filter and a wiring harness fishes through.

There are some open areas going to the side compartments where the bottle are, so that must be where it is getting it from.
I'll run it and see where I can feel air moving.

The idea of just skipping the front compartment underpinning and running the underpinning across a little further back is probably the safest way to go 👍
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Old 01-14-2025, 08:41 PM   #8
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....
The idea of just skipping the front compartment underpinning and running the underpinning across a little further back is probably the safest way to go 👍
Use an Infrared thermometer and measure the floor temperature before and after and let us know. It depends on how well insulated your RV is.
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Old 01-15-2025, 06:34 PM   #9
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Use an Infrared thermometer and measure the floor temperature before and after and let us know. It depends on how well insulated your RV is.
They are supposed to come fix the heater on Friday, and the big freeze starts Sunday night. I'm not staying in it yet, but I'll probably wait until this hard freeze is over next week, then see if I can get the underpinning done and get moved in 👍
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