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Old 04-26-2010, 11:20 PM   #1
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Attic fan


Hello. I want to install a fan in the attic, and I want to connect it to
an existing line. I have a circuit only for a kitchen vent. In the
attic there is a flexible cord connecting to the vent. I want to
start at the flexible line and connect to the attic fan.
The problem with this idea is that if I turn the kitchen vent
on, then the attic fan will go on too.
Any other ideas ? How can I connect to
the kitchen vent line, but being separated.
The existing vent is 20 Amperes which is fine. I just try to
figure out how to connect to the kitchen vent but ate the same
time be separated.

CIRCUIT BREAKER---TO---SWITCH---TO---VENT
I START NEW LINE AT VENT---TO---ATTIC FAN
Thanks.
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Old 04-27-2010, 09:08 AM   #2
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You would need to branch off the unswitched power, which would probably be at the light switch. If you tap into the line feeding your kitchen vent, your attic fan will turn on with the kitchen vent.

You'll need to run a new wire from a hot feed to a new switch then to the new fan.
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Old 04-27-2010, 10:35 AM   #3
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Attic Fan


Thanks for the advice. It is not crystal clear for me where is
the unswitched power. And start the new line.

CIRCUIT BREAKER---TO----SWITCH----TO----KITCHEN VENT
Where Do I start the new line ? After the circuit breaker and
before the switch ? Thanks.
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Old 04-27-2010, 01:23 PM   #4
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Quote:
Originally Posted by Gabriel24 View Post
Thanks for the advice. It is not crystal clear for me where is
the unswitched power. And start the new line.

CIRCUIT BREAKER---TO----SWITCH----TO----KITCHEN VENT
Where Do I start the new line ? After the circuit breaker and
before the switch ? Thanks.
Yes, somewhere before the switch. This can be in the box where your switch is, or before that box. The line feeding the switch is "unswitched" power. The line coming from the switch to the vent is "switched" power.
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Old 04-27-2010, 02:14 PM   #5
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I would run a new 20 amp circuit to a switch or thermostat then on to the fan. It's a motor load and whole house attic fans can be good size residential motors.
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Old 04-27-2010, 05:52 PM   #6
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Attic Fan


Thanks J. V.; Thanks Secutanudu;
I think it is all clear: I am going to start inside the box where
the switch is located; but I am going to grab the power from the
black wire just before the switch. I am going to install those special
switches which have two buttons and I am going to cut the brass
tab. One button will be for the vent and the other button will be for
the attic fan.

Last edited by Gabriel24; 04-27-2010 at 05:54 PM. Reason: spelling
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Old 04-27-2010, 09:34 PM   #7
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Keep in mind what J.V. said. A dedicated circuit may be a better idea. Also, you do not need to break the tab on the double switch.
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Old 04-28-2010, 10:41 AM   #8
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Quote:
Originally Posted by Gabriel24 View Post
Thanks J. V.; Thanks Secutanudu;
I think it is all clear: I am going to start inside the box where
the switch is located; but I am going to grab the power from the
black wire just before the switch. I am going to install those special
switches which have two buttons and I am going to cut the brass
tab. One button will be for the vent and the other button will be for
the attic fan.
Be careful. What else is on the circuit? What size is the breaker? What size motor is on the fan? What is the current required to operate the fan motor? Do you have the fan specs? If you do not know these answers you better get the answers before you start. I have seen to many people do what you are doing to find out the load was to great for the circuit. This will cause the breaker to trip and you will have to start all over again.

If you have a switch like the one pictured, you do not break any tabs. You will need a jumper for the neutral terminals if you do.
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Old 04-28-2010, 02:32 PM   #9
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If you're prone to ice dams I recommend a switch that can bypass the fan's thermostat if it has one.

Yes, I know that UL will have a conniption about this, but it's your house. As informed adult[s], you judge the risk/benefit. I've corresponded with UL on another issue, and they are as political as any organization.

Last edited by Yoyizit; 04-28-2010 at 02:37 PM.
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Old 04-28-2010, 03:21 PM   #10
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Quote:
Originally Posted by Yoyizit View Post
If you're prone to ice dams I recommend a switch that can bypass the fan's thermostat if it has one
I actually wired an attic fan exactly like this -more for summer use
Thermostat turned it on/off automatically, but it would shut off as Temp dropped below maybe 95/100
So about 9-11pm at nite when it was cooler (50-70) I would flip the switch & run the fan to really cool the attic off



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Old 04-28-2010, 04:47 PM   #11
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Attic fan


To continue what J.V, YOYIZIT, SECUTANUDU, SCUBA DAVE, replied:
In south Calif. we never have ice dam, it never snows.
On the circuit there is a 20 AMP line for the kitchen vent.
The size of the motor and the amps is 20 AMPS, the wire is
going to be 12 gage. No Thermostat. I use the attic fan only
on those hot summer days.
The swicth like the one in the picture, and no breaking brass tab.
Thank for all your input.
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Old 04-28-2010, 05:10 PM   #12
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Quote:
Originally Posted by Scuba_Dave View Post
I actually wired an attic fan exactly like this -more for summer use
Thermostat turned it on/off automatically, but it would shut off as Temp dropped below maybe 95/100
So about 9-11pm at nite when it was cooler (50-70) I would flip the switch & run the fan to really cool the attic off
I never thought of that use.
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Old 04-28-2010, 07:15 PM   #13
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Within the last two (2) months here in S. Ga., there have been three (3) homes burn to the ground with the State Fire Marshall's Office ruling that "Attic Fans" have caused the fires. I have seen too many of these fans with burned-out motors, the motor not turning, but still humming and smoking when I go up to check them. ALL of these have been tied into circuits with something else whereas the attic fans will not pull enough amps when the motor stops to trip the breaker. I now use an inline fuse holder, only five (5) amps/110 V, dedicated to the attic fan motor only. A small task, but I feel that it's protection will be worth it if needed. Just a thought, David
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Old 04-28-2010, 08:28 PM   #14
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Quote:
Originally Posted by Thurman View Post
Within the last two (2) months here in S. Ga., there have been three (3) homes burn to the ground with the State Fire Marshall's Office ruling that "Attic Fans" have caused the fires. I have seen too many of these fans with burned-out motors, the motor not turning, but still humming and smoking when I go up to check them. ALL of these have been tied into circuits with something else whereas the attic fans will not pull enough amps when the motor stops to trip the breaker. I now use an inline fuse holder, only five (5) amps/110 V, dedicated to the attic fan motor only. A small task, but I feel that it's protection will be worth it if needed. Just a thought, David
I thought these motors are req'd to have internal overload protection and are labelled as such. Probably it trips based on internal temps of the windings.

Specifying the clearing time for a fuse for a motor can be tricky.

Whether the motor runs because of a 'stat or because it was switched from elsewhere shouldn't affect motor reliability.
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Old 04-30-2010, 05:49 PM   #15
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Wiring Drawing


This is a wiring drawing.
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