Depends on the cfm (cubic feet per minute) of the fan. This will tell you how much it's working to replace the air in your house.
Also depends on your current circuit, and your circuit current, lol. I'm willing to bet that the current circuit is 20amp, so I don't know why he's trying to replace that. I'm willing to bet the fan is also using almost all of the available circuit. You need to find out what the draw is on the fan for that. A 20amp circuit can handle 2400 watts. But due to code limiting draw at 70%, you can only put 1680w on there legally. That's for saftey(fire) reasons.
Also, is this supposed to replace the air in the house, and attic? Because 3000cfm is akin to a wind tunnel. That would replace the air in an attic and house in about a minute. Without proper air exchange points, that actually sounds problematic to seals.
The fans only would remove air from the attic. I didn't consider the seals. I'll make sure to bring up the air exchange points when I talk to the handyman again, but I'm considering dropping him. Thank you for your comment.
As a 25 year construction worker, many of which have dealt with electricity. Two full years as an electrician.
Running one 240 circuit might sound intimidating. But it's an efficient way to run a lot of juice to one location. All of your large appliances are ran on a 240, if they're electric.
I can't exactly explain to you why, but most efficient electric motors are 240. I agree with his initial recommendation. Without being on site, or having exact measurements, I cannot say that the cfm is uncalled for. I was going off of your 1300sqft est on the attic.
Just know that the things you are looking for are appropriate air exchange. Not too much, not too little.
Edit
With 240, it's more about the amperage. Basically he's talking about still running two 20A circuts, but in one wire. Level two car charges are like 48A 240, and level three is like 100A 240.
I appreciate your comment, and I agree and understand that some appliances function better off of 240 volts, but with this extra context, wouldn't this particular fan not benefit from a 240 volt line because the unit is only rate to operate at 120 volts? I believe this would damage the fan, or outright destroy it.
So with the whole 240/120 thing you're talking about phases. These are basically electrical currents that function like wavelengths, operating at specific frequencies. The amperage basically says how much punch that phase/frequency can have.
If you put two twenty Amp circuits on the same neutral. The electricity will pass through both motors, and come back to the panel. The panel will read that those breakers are putting out more than 20A and trip the breakers.
BUT
If you put those breakers on different phases, the wavelengths alternate. Instead of really high peaks and valleys, there are more frequently occurring similar ones. So the breakers will read with in limits, and function. This is called sharing a neutral
What your guy is trying to do, is save a lot of work, and some money on material. Instead of running two wires, he's trying to share neutrals.
Each fan would be 1500 cfm. I'm guessing the attic is about 3500 cubic feet.
I forgot to say this, but the current circuit, as far as I can tell, doesn't connect to the breaker box. The lines are dead and the attic ventilation fan hasn't worked since we bought the house. The fan doesn't spin smooth when manually rotated, so we assumed it needed replacing.
The handyman originally insisted on installing a 240 volt wiring and circuit breaker. I don't know much about electricity but that set off red flags. I have no problem going with higher gauge wiring if the cost is cents more, but there is no reason to run that many amps unless we're plan on charging an electric car in the attic.