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strider3700 · 10-03-10, 12:51 AM

I know I'm digging this one up from way in the past.

I also have one of those swordfish UV lights in my furnace. It is only really effective at killing things when the fan on the furnace is running which is less then 10% of the time at the most in my case. So since the light uses 30ish watts sitting there purifying the exact same bit of air 90% of the time I spoke with a friend in the control systems industry. After looking at the wiring diagrams for my heatpump/furnace he hooked me up with a 24V-110 relay and I poked around with a multimeter while my wife turned the fan on and off at the controls until I found the right lead.

I then wired the relay to turn on when the fan turns on. Then I cut the wire going to the Light and switched one lead on it with the relay.

Anyways the end result is my light only turns on when the furnace fan is running. which should roughly save me just shy of $20/year and should greatly extend the life expectancy of those bulbs.

If your fan happens to be 110V you can probably just tap power directly off of it and not need the relay.

10-03-10, 12:51 AM	#16
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	I know I'm digging this one up from way in the past. I also have one of those swordfish UV lights in my furnace. It is only really effective at killing things when the fan on the furnace is running which is less then 10% of the time at the most in my case. So since the light uses 30ish watts sitting there purifying the exact same bit of air 90% of the time I spoke with a friend in the control systems industry. After looking at the wiring diagrams for my heatpump/furnace he hooked me up with a 24V-110 relay and I poked around with a multimeter while my wife turned the fan on and off at the controls until I found the right lead. I then wired the relay to turn on when the fan turns on. Then I cut the wire going to the Light and switched one lead on it with the relay. Anyways the end result is my light only turns on when the furnace fan is running. which should roughly save me just shy of $20/year and should greatly extend the life expectancy of those bulbs. If your fan happens to be 110V you can probably just tap power directly off of it and not need the relay.