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Old 06-18-2021, 04:42 PM   #1
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Heatwave! Use roof vent fan with A/C?

We are renovating an old 34' class A motorhome. We have it plugged in to shore power at our home (husband installed a 50amp breaker and plug receptacle).

We are in AZ having 116F temps! The rig has 2 AC units but we are leery to run both while still running our home AC. We haven't yet installed our hardwired EMS.

Soooo.. the question is whether it is advised to open and run our roof vent fan (in the main area of the rig) while also running the AC. Is this counterproductive? The AC has been running since morning but the inside rig temp (at 3:30pm) is reading 104F.
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Old 06-18-2021, 04:50 PM   #2
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Obviously one AC unit is inadequate, chances are that even two units would be insufficient. I would try multiple fans to move the air.
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Old 06-18-2021, 04:58 PM   #3
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^ Agreed. One unit is insufficient.

The roof fan vents air (presumably) from inside to outside... Is that just pushing out the cool air that the AC is producing or is it helping move hot air out of the MH?
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Old 06-18-2021, 04:59 PM   #4
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Your house has plenty of power if it's a 100 amp service or better. It would be pre 1960 to not be.
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Old 06-18-2021, 05:00 PM   #5
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I also doubt 2 ACs would cool it off. Forget about renovating until the temps cool way down. Or.... pack your renovating stuff and move up to Flagstaff, Pinetop or Greer!
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Old 06-18-2021, 05:03 PM   #6
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Quote:
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^ Agreed. One unit is insufficient.

The roof fan vents air (presumably) from inside to outside... Is that just pushing out the cool air that the AC is producing or is it helping move hot air out of the MH?

There is no cool air (104*) to be vented, only hot air.

Like many soldiers I survived two summers in a "hot place", large fans made it tolerable.
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Old 06-18-2021, 05:19 PM   #7
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There is no cool air (104*) to be vented, only hot air.
Haha... yes, I suppose you are correct!!
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Old 06-18-2021, 05:38 PM   #8
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I dont think the fan and AC will work.. I know when its hot and we are running the AC, and we cook something and run the fan the camper warms up a few degrees. The air that is pushed out has to be replaced by air from outside.
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Old 06-18-2021, 05:53 PM   #9
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I know that when it is over 95 here in Texas 2 A/Cs are barely enough to cool off our 30 foot Class A. It become tolerable but not cold. Some days both A/Cs will run until 10 or 11 before they shut off.
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Old 06-18-2021, 06:13 PM   #10
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Any chance you could knock together a quick frame and put a tarp over part of it even? Most RVs only have a couple of inches of insulation. With that kind of sun beating on it he's working in a furnace.
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Old 06-19-2021, 05:40 AM   #11
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Quote:
Originally Posted by Time2roll View Post
We are renovating an old 34' class A motorhome. We have it plugged in to shore power at our home (husband installed a 50amp breaker and plug receptacle).

We are in AZ having 116F temps! The rig has 2 AC units but we are leery to run both while still running our home AC. We haven't yet installed our hardwired EMS.
With a 120/240V feeder to your coach, presumably each A/C unit is on its own leg (L1 and L2 from the main panel). So each one is pulling something like 15A or so. Your home A/C, depending on number and size, might be drawing 40A or more from both L1 and L2, since it/they’re 240V units. The two coach units add to that. But that’s still way under 100A on each leg, and 100A is small for a residence service size in the last 50 years, which is more likely 150-200A anyway.

Or put another way, adding 3600VA to a system capable of 24,000-48,000VA is not likely to be a problem, but if it worries you, don’t run the clothes dryer at the same time (~5000VA - more than both RV A/C’s combined).

Quote:
Originally Posted by Time2roll View Post
Soooo.. the question is whether it is advised to open and run our roof vent fan (in the main area of the rig) while also running the AC. Is this counterproductive? The AC has been running since morning but the inside rig temp (at 3:30pm) is reading 104F.
As someone said, if you’re blowing inside air out through the roof, other air has to come in through the cracks and windows, and if that air that’s coming in is 116F, you’ll be shoveling sand against the tide. Seal it up, shield it from the sun the best you can, and put a fan inside to move air around. That’s all you can do.

Oh, you could also add a portable A/C unit, which will have to be vented out a window, but I see folks here posting about using them with pretty good success, so that’s an option. And I still wouldn’t worry about the power draw.
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Old 06-19-2021, 09:06 AM   #12
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Reflxit on the outside of the windows is the most effective way to cool it down. You can put it on the inside of single pane windows but it's less effective.
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Old 06-19-2021, 09:44 AM   #13
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Look in your circuit breaker box. There should be main breakers. If they are 150 and or greater. You will be fine to run the camper 2 ac's. If they are 100 amps most likly you are fine. Most houses AC units draw between 17 and 30 amps.

But rember, if you draw to much the circuit breakers in the house should be designed to trip.
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Old 06-19-2021, 10:03 AM   #14
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I agree. Run exhaust fans or run two A/C's. Add a room fan directed at the workers for added cooling in either case.

Running A/C and exhaust fans at the same time is pointless. Try it. You will see.

House power will carry the load for two RV A/C's. Worst case is house circuit breaker will trip. Just reduce loads in the house and reset the breaker.

I wish you good luck and happy trails ahead!
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