Handyman suggested cutting hole in 1330 sq. ft. attic for second attic ventilator. Does this make sense?

protist, 15 days ago (edited 15 days ago)

What reason does your handyman give for needing a second fan in your attic? What’s going to be different for your house? I’m assuming your attic is a typical uninsulated attic in the US. I live in Texas, and as far as the eye can see there are houses with uninsulated, passively-ventilated attics. Almost no one has powered attic ventilation. I have a thick layer of blown-in insulation up there, and with the volume of air your handyman wants to move, I’d be concerned the insulation would move with it.

In an ideal world, all our attics would be inside the insulated envelope of our homes, but our building standards are not there. So where you can affect energy efficiency is in improving the impermeability of your insulation as it currently exists. If you’re going for energy efficiency, slightly lowering the ambient temperature of your attic in the summer heat is just not an effective solution. Spend that money instead on fully sealing all the holes around joints and fixtures that are currently leaking air between your living space ceiling and your attic, and improving the R value of your attic insulation.

I don’t know if what I’m talking about applies to your house, but if so, check out this Matt Risinger video for a lot more detail.

TheDorkfromYork, 15 days ago

First off, thank you for the advice.

The reason the handyman gave for installing two fans was basic, to improve the dispersal of hot air. My partner and I concluded that removing heat would be the most effective first step to decreasing the temperature of the house, but we can be talked into considering insulation first. We’ll look into leak patching and into insulation.

Do you happen to know if during the winter months, if insulation would significantly block the house from being heated by the sun? We are looking to get a heat pump in the long run and originally planned to have the insulation done at the same time, but in the meantime, winters can get cold here and any heat we get goes a long way.

stands_while_poops, 2 days ago

If you’re gaining heat from the winter sun you’re likely losing more heat than you’re gaining from poor insulation.

TheDorkfromYork, 2 days ago

Good point. Thank you.

protist, 14 days ago

Improving the insulation barrier between your ceiling and attic will only serve to increase your home’s heat retention in the winter. When it’s cold outside, the sun heating your attic is not going to increase the heat in your home more than the cold ambient temperature in your attic is going to decrease it. Before you pay to have this work done I’d genuinely consider whether there are other projects that would be much more impactful you could do instead. Definitely get other opinions from contractors first (never just get one quote for any project, prices and recommendations can vary widely) and see if you can get a certified home performance contractor to take a look at your goals

stands_while_poops, 2 days ago (edited 2 days ago)

3000CFM is probably too much. Your exhaust needs to match your soffit intake in terms of how much air they move. You can’t just exhaust air without replacing that air. Find a roofing contractor and not a handy man. If you’re forcing 3000CFM out and your soffit vents combined allow for 1000CFM, there are still 2000CFM that need to come from somewhere and it could start coming from your conditioned space through air leaks from things like light fixtures and drywall gaps.

It sounds like you’re wanting to vent the attic to cool the house? If so, insulation is your best bet. Yes it may also prevent you from gaining heat in the winter from the sun, but it will also keep the heat from your HVAC inside which is way more efficient than relying on an insignificant amount of heat from a winter sun. We recently increased our insulation to R50 and it has helped lower our bills and equal out the temperature of the house

pdavis, 13 days ago

I thought ridge vents were all the rage these days. I installed ridge vents and then put up Reflectix Reflective Roll Insulation from the soffits up to 12-18 inches from the ridge. It reduced the heat in the attic by a noticeable amount and wasn’t too expensive or difficult to install. I also blew in additional insulation. I plan on adding additional venting in the soffits in the future. My experience is that fans fail, require maintenance, use energy, and tend to only cool the attic off in certain areas if not well planned out with supporting architecture and venting.

Acedia, 15 days ago

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.

Acedia, 15 days ago

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.

TheDorkfromYork, 15 days ago

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.

Acedia, 15 days ago (edited 15 days ago)

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.

If you have an electric stove, that’s 50A 240

intensely_human, 14 days ago

Is it possible the 1500 cfm fans are intended to be run at lower capacity, and are just sized for a factor of safety?

TheDorkfromYork, 15 days ago

So the product he is installing, on Amazon, says it runs off 120 volts. Here is the link to the amazon listing.

www.amazon.com/…/B01AA6Y2YS

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.

Acedia, 15 days ago

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.

TheDorkfromYork, 15 days ago

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.

Thank you for your comment.

apfelwoiSchoppen, 15 days ago

Yeah, that 240v line run suggestion puts a gigantic question mark on anything they’ve suggested at all. I’d recommend a second opinion.

BearOfaTime, 15 days ago

240v for an attic fan? Wtf?

Yea, fire this “handyman”. 240 in the US is for high load devices, like AC, electric stove (electric heat is a direct short), electric water heater.

A fan draws a very small amount of current - less than 5 amps at 120v.

I have a small portable blower (this uses a compressor wheel, so draws more current than a fan), and it’s rated for 5 amps.