Foo - Whole house fan -- separate circuit?

Does a whole house fan require it's own circuit? We just bought one, but I think it's only 1/3HP, a modest current draw. I don't see why it couldn't tap from the circuit powering the attic, which is never used anyways, but I thought I'd check anyways.

Depends on the amps and voltage being sucked up. Check the manufacturer specifications label.

If it you just hook it into the circuit that goes to the attic, unless you built your own house or ran all the wire, you can't be certain what is tied into it.

anectdotal evidence but in my house, my parents and my sister's, they are all on their own circuit.

120v @ 3.4A on high. We can be certain what is tied into the attic circuit though; turning off the breaker only shuts off power to the attic!

Our whole house fan is (stupidly) tied into one of the bedroom circuits. The attic circuit sounds like the best one to power your fan. If you wire it yourself, be careful about wiring methods. If you run NM-Cable (aka "Romex"), there are rules about protecting the cable from damage. Post if you're not sure what that means and are planning to wire it yourself.

Does a whole house fan require it's own circuit? We just bought one, but I think it's only 1/3HP, a modest current draw. I don't see why it couldn't tap from the circuit powering the attic, which is never used anyways, but I thought I'd check anyways.

I used one when I put mine in.

120v @ 3.4A on high. We can be certain what is tied into the attic circuit though; turning off the breaker only shuts off power to the attic!

That's only about 400W. A typical circuit in a house is 15A max, so if there's nothing else huge on that circuit, you should be fine.

Ok I'll try not to bore you to much but here it is, According to the NEC (National Electrical Code)
article 430.42 (A) Motors not over 1 Horsepower. One or more motors without individual overload protection shall be permitted to be connected to a general purpose branch circuit only where the installation complies with the limiting conditions specified in 430.32(B) and (D) and 430.53(A)(1) and (A)(2).

430.32(B) This article basically states that your automatically starting motor must have a separate overload device. and it doe's it's called a thermal overload, attic fans are built with them.
Article 430.53(A)(1) and (A)(2) deals with multi motors and this does not apply to you.

Ok, basically this means yes you can install the fan on that circuit and it will be safe.
The bad news is it sounds like this is a dedicated lighting circuit and that brings this complication, by installing the fan it will be considered as HVAC equipment and such equipment is by code required to have a separate receptacle and lighting circuit for purposes of maintenance, basically what this means is if you call me to work on the fan at some time I should be able to shut off the power to the fan and not lose the lights or recpt.(This is covered under multiple article of the NEC)

So here's the real question, do you plan to sell the house in the near future?
Will this work be inspected by your city code official?

If the answer is no I would simply do this.(not 100% by the book but safe.)
If there is no recpt. in the attic install one next to the light switch, be sure to use the same size wire that is there already.
Run the new wire from the new recpt. to the fan location, install a switch (this will allow me to shut of the fan to work on it with out shutting of the lites.) run a small length of wire to the fan junction box.
Run all wire to follow the wood structure away from walking areas or up in the rafters if you have a truss roof, or just run it as high as you can on the rafters.
BE SURE TO DISCONNECT THE POWER BEFORE MAKING CONNECTIONS THEN TEST AND MAKE SURE IT IS OFF.

your list of materials

2-nail on 1gand plastic boxes
1-duplex receptacle
1-single pole switch
1-duplex cover plate
1-single switch plate
1-romex connector(this will attach to the fan junction box)
x-feet of wire 14-2 of 12-2 romex
x-wire staples for above wire

Any yes iv'e been a master electrician for nearly 15 years

Presuming you have identified an unswitched power source, the biggest PITA is running wire and installing the switchbox in your already finished walls

3.4 amps? If the circuit that feeds the attic is on at least a 15A breaker and nothing else is hooked up there (other than lights) - go for it.

Yup, sorry I took so long to reply again, but sounds like you're fine.

Hey thanks for the good replies. This circuit does provide power to our two lights in the attic as well as a couple of 120v outlets; I was going to tap from the outlet box. The switch we use to turn the lights off and on the attic does not shut off power to the receptacles.The fan includes a pull chain to toggle between high and low speed, but I'm guessing this also turns it off and on (the fan arrives from Grainer Tuesday of next week).

So it sounds like all I need is a switch to shut off power for servicing. No big deal! Can I assume it only needs to be an normal toggle switch and not a more industrial looking shutoff switch?

I have tons of 14ga NM cable ready to be used, but I've also got some 1/2" EMT with THHN that I'd like to make use of. It might be weird, but I enjoy bending conduit.

I'm interesting in how noisy this thing is going to be. A 30" direct drive model that pushes 5700CFM on high, I'm told it can sound like a helicopter landing on the roof :p. I may mount it a few inches above the ceiling -- perhaps above the rafters -- to offer relief.

If you run a 20 amp circuit (I'd pull it up the stack from the basement) I think you should use a 20 amp switch.

That's what I'd do. It doesn't cost much more. I don't know what the code says about that.

Whole house fans are extremely loud, but if you live in a place that's hot during the day and relatively cool at night, they're very much worth the noise.

I don't know that I'd assume that the pull chain is high-low-off. The one in my house has two wall-mounted controls: on/off (actually a timer, which is very nice to have) and high/low. On the other hand, there being a pull-chain in the first place may indicate a more ceiling-fan type of operation, so who knows.

Well the fan is mounted on the ceiling. I could install a shutoff switch on the wall if I wanted, or even a timer; that's a good thought. We've definitely concluded that a whole house fan is a good option for us. What if I added ducting from the large cutout on the ceiling and had the fan mounted elsewhere in the attic. This would, as well being unconventional, be less noisy.

Well the fan is mounted on the ceiling. I could install a shutoff switch on the wall if I wanted, or even a timer; that's a good thought. We've definitely concluded that a whole house fan is a good option for us. What if I added ducting from the large cutout on the ceiling and had the fan mounted elsewhere in the attic. This would, as well being unconventional, be less noisy.

I guess I should have asked before, I thought you were getting a roof or gable mount fan that would draw the hot air out of the attic, they typically have a built in thermostat and run automatically.
can you provide the Grainger model # or a link on there web page? it may still be able to be Gable mounted and vents put in the ceilings in several rooms.

I guess I should have asked before, I thought you were getting a roof or gable mount fan that would draw the hot air out of the attic, they typically have a built in thermostat and run automatically.
can you provide the Grainger model # or a link on there web page? it may still be able to be Gable mounted and vents put in the ceilings in several rooms.

I took it that the OP was asking about a fan that sucks heat out of the living space and dumps it INTO the attic, efficiently causing cooler air outside of the house to come in via open windows.

Also...You like to bend conduit? Crazy.

I drank boiling water and figured out how to rewire my whole house.

I like the idea of having it on a separate, GFCI protected circuit, so one doesn't have to worry about sharing power with it, but it may be too much expense.

I took it that the OP was asking about a fan that sucks heat out of the living space and dumps it INTO the attic, efficiently causing cooler air outside of the house to come in via open windows.

Also...You like to bend conduit? Crazy.

Yea, I just wasen't even thinking in that direction those type of fans are rare to see in this area.
The people that do have them don't like the noise they make.

I drank boiling water and figured out how to rewire my whole house.

Thats the plumbing department, Next isle over:D

I like the idea of having it on a separate, GFCI protected circuit, so one doesn't have to worry about sharing power with it, but it may be too much expense.

A separate circuit would be ideal, GFCI would be a waste and AFCIs don't always like motors.

http://www.grainger.com/Grainger/wwg/productIndex.shtml?from=Search&newSrch=yes&operator=keywordSearch&search_type=model&action=Go!&QueryString=WH302MLX&submit.x=3&submit.y=0

that is the fan I bought.

Whole House Fan, Direct-drive, 2 Speed, Propeller Dia 30 In, CFM High 5700, CFM Low 4275, HP 1/3, Fan RPM 775/600, Voltage 120, 60 Hz, Single Phase, Amps 5.6/1.5, Height 7 In, Width 34 In, Depth 34 In, Ceiling Mounting Location, Includes 2-speed Pull Chain Switch and White Shutter

Its calling for 5.6 amps, as long as the recpts on that circuit don't have a large draw you should be OK, but I would consider running a new circuit. also make sure the attic is properly vented the air must have a place to go ie. gable vents or eve vents if not the fan will not work properly.

I installed the fan yesterday, took about 4.5 hours plus time to clean up the drywall dust. The fan is loud!!! Per the instruction's suggestion, I have pieces of rubber in between the frame of the fan and ceiling joists to absorb some of the vibration. Still, on high, it sounds like a wind tunnel. Wildly effective though. I put it on high and used compressed air to blow the dust into the air and the fan sucked it all up.

As far as ventilation goes, I have 3 gable vents plus vents all along the bottom of the roof on both sides of the house. I'll calculate how many sq feet this is today and deduct 30% to compensate for the grill/screens on each vent.

I'd prefer to see it's own circuit as well. The problem is that the route the cable would need to take from my basement subpanel is very awkward. Honestly, without removing a lot of drywall, I'm not sure how I'd do it; the original wiring is existing and was obviously erected while the house was being constructed. One option would be to go outside the house, running PVC conduit. This would be a fairly direct route, but I just don't know if I want to go down that road.

Sounds good, as long as the fan doesn't trip the breaker I wouldn't worry about it,
chances are you don't have a huge draw on that circuit any way.