Adding Aux HVAC fan

I am adding an auxillery fan to my HVAC. Actually two; One for my computer room where the computers keep it rather toasty, and one for my bedroom where the large number of windows keep it rather 'outsidey.'
I want to start with the bedroom one which is already installed in the duct. I have run the wiring to the furnace area. 3 wires; power and ground. Wiring nailed into ceiling floor joists, etc.
The question is what to do now? I want to use a relay so the aux fan comes on when the HVAC blower is on.
So I have a relay that I need to mount somehwere. Its coil will be on the HVAC control which IIRC is 24vac. Its NO contact will connect from a switch which will be powered by the main furnace switch next to the furnace. This is lookin nasty though as it seems I need to install some connectors on the wires and plug them in, or maybe find a relay with screw terminals!?
I am assuming this relay needs to be mounted to something and in some kind of enclosure? I intend to put it in a normal switch box mounted to a floor joist in the ceiling.
I am assuming the wiring needs to be in metal pipes? Also does the 24vac need a seperate pipe from the 120vac wiring?
Is there a simpler way?
This is a pretty small fan which I believe is < 1A load for 120VAC. I'm an electrical engineer but not an electrician. I don't know the rules but I'd like to follow them if I can learn them.
--
Respectfully,


CL Gilbert
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With all due respect:
Adding aux fans is the LAST thing you do.
If you have a cooling problem due to airflow, the fans may mask it, but they will not cure it.
You can only get X-CFM down a duct of X-Diameter at the proper static pressure. Velocity of the air has to be taken into consideration and if your aux fan will not handle what you need to equal the proper airflow to deliver enough BTUh back to the unit, then you have wasted time. Normally, air flow issues are due to poor duct design, or proper duct design based upon the original use of the home, or room, and if you have added a heat load to it, then adding a fan to try to increase the air flow to the room prob wont help, and even if it does, what have you done to the balance of the system?
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Carolina Breeze HVAC wrote:

Well this is all I could think of. As I stated, the bedroom's temperature is off in my opinion due to higher heat loss than other rooms due to so many windows. It also has a vaulted ceiling.
The computer room stays HOT, even in the winter due to added heat sources within the room. The rest of the house is pretty nice, including even the basement. I can't keep the doors open since my Son would enter the room and put his signature on it...
So increasing cooling in summer and heating in winder to the bedroom is my objective. So I added a fan...For the computer room I could drill holes in the wall, and run a radiator outside and cool my computers with a water cooling system. But im hoping for something less obtrusive.
The master bedroom is the farthest room from the furnace, being on the 2nd floor and other side of the house. The computer room is on the 2nd floor, but basically above the furnace.
Perhaps for the computer room I could put the fan on the return?
Ideas?
--
Respectfully,


CL Gilbert
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Have you considered putting a window unit in the computer room?
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I don't know how hot your computer room gets. In my home office there is a 2k VA Tripplite UPS, 4 tower PC's, 2 of which run 24x7 along with ham radio gear that runs all the time and big old 20 amp dc power supplies to run the ham gear. Add to that 3 CRT style displays a laptop computer, battery chargers, printer, 2 routers, a switch, a couple of police scanners, and a small Merlin PBX. Room size is 9 x 15. A/C in room next to it but no A/C duct in this room. A ceiling fan in the computer / office seems to keep the air mixed up enough to be comfortable even when it is 98 degrees outside.
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Steve Stone wrote:

Thats amazing. Im running an AMD XP3200+ and an Ati 9700Pro graphics card. This computer is a heat box. Its the real heat generator and the room is hot but bearable before I turn it on. Laser printer is there too but the heat is not too much.
Im seriously considering the 'Reserator' silent water cooling system to get the heat out from under the desk.
I should also mention this room is 1/2 over the garage, and the garage gets HOT as well.
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Respectfully,


CL Gilbert
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CL (dnoyeB) Gilbert wrote:

Might want to see what kind of temps you're running. http://www.almico.com/sfdownload.php
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CL (dnoyeB) Gilbert wrote:

As others have said, I would look first to rebalance the HVAC system, etc. before using a booster fan.
If the final conclusion is to use a booster fan, one alternative to adding a relay is to put an airflow sensor in the duct. That way, once the heat or A/C comes on and starts blowing air through the ducts, the sensors picks that up and will close a NO switch. All you have to do is run 120 VAC to the sensor, and then he switched 120 VAC to the booster fan. No electrical connections to the HVAC system are required.
My furnace has a relay on the circuit board for activating auxillary equipment, such as a humidifier that I have for during the heating season. Check the manual to see if you have this and if it will support the load your fan will put on it.
If you have to add a relay, then see if you can add an electrical box right on your HVAC system. I was able to do this on my system (just to make some connections, no relay was required...) by just putting a regular junction box and attaching with standard electrical fittings to the electrical box that was part of the furnace. It already had knockouts for just such a connection. I know nothing about this, but if I was in your shoes I would call an HVAC place and I'm sure they have some sort of relays for just these sort of purposes that they would be willing to sell you.
Ken
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Get an Aprilaire current relay #50 or #51. It clamps around the common blower wire and senses the blower motor current. One switches 120 volts, the other switches 24 bolts, I don't remember which is which. Each relay will carry 1 amp.
That being said, the best solution would be to run a load calculation to determine how much air each room needs and resize your ducts to get the right amount of air in every room. Note that is not a job for an amateur. It would be the best solution to your problem.
Most "booster fans" are propeller fans. They do not produce the high static pressures needed for duct systems and are not very effective. You may not want to run it that way for the computer room in the winter since it is too hot there anyway. In the summer run the computer room fan 24/7. Just plug it in to a wall outlet.
The bedroom fan unit can be on a relay. The relay can be mounted inside the furnace control cabinet for safety.
Good luck.
Stretch
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