Vent Fan. How much for a mobile, marine, or off-grid electrical academy?

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Vent fans don’t take much power by themselves, but they are typically in use for HOURS per day, which is why they need to be accounted for when sizing  the batteries and solar in a mobile, marine, or off-grid electrical system, and that’s exactly what I’m going to teach you here in lesson #9 of this Electrical System Sizing chapter of the Mobile, Marine, and off-Grid Electrical Academy.

Now the methods of estimating power usage I’m going to teach you in this video will work for many different electrical devices, so if you keep an open mind and think critically, you’ll be able to apply this information to your own specific project.

Vent Fan. How much power for a mobile, marine, or off-grid electrical system VIDEO

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How Much Power does a Vent Fan Use?

The instruction manual for the MaxxFan Deluxe says that it requires a 5 amp, 12V service.

Now this is a good starting point, and we ‘could’ say that 5 amps x 12V = 60W multiplied by 10 hours per day results in 600 Watt hours; BUT…  that would be an over-estimation because the 5 amps the device uses is partially due to the amount of power it takes to raise the lid, which only takes a couple of seconds and doesn’t really need to be factored into a power audit as the load is so small.

The MaxxFan Deluxe also has 10 different speeds, and most people aren’t running it on high all of the time, so we should also take that into consideration.

I went out and ran through all the MaxxFan speeds and measured their power draw in our van, and here were the results.

Now trying to say that: “From 7am to 10am, I’m going to run the fan at 40%, which is 7.5W… and then from 10 to noon – 70%, which is 19.4W… And then it gets hot after noon, so I’ll run it at full speed for 3 hours, which is 43.4W

After that, I’ll just turn it off for 4 hours and use the air conditioner

Well, that math would get complicated in a hurry to get that exact, so here is a more simplified plan.

When Steph and I lived in our van full time, it seemed like we would have the fan on high after the sun came up, and then on low after the sun went down.  

So for easy figuring, we could say that we ran the fan on speed 10 for 16 hours, and then on speed 1 for 8 hours.

This results in 43 watts for 16 hours and 2 watts for 8 hours which results in ((43×16)+(2×8)) = 704 watt hours.

How much power does a vent fan use from a battery bank?

In the context of an off-grid battery bank, if this power were being drawn from a 12V battery, 704 watt hours divided by 12V results in 59 amp hours, which is 59% of a 100Ah 12V battery for those 24 hours of fan usage at those two speeds.


Now you should have a good idea of how to calculate the power used by your vent fan in a mobile, marine, or off-grid electrical system.

We will refer to this lesson later in this academy when we discuss full power audits, so be sure to bookmark it for future reference and come back to it if you need a refresher.

In the next lesson, we are wrapping up this system sizing playlist with the grand finale: A complete start-to-finish power audit.


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