One problem, most modern air handlers have an expensive circuit board which has a relay mounted on it to control the blower motor. If the OP somehow shorts it out, it will cost him dearly. Many of those circuit boards have an on-board fuse rated at 3 to 5 amps to protect the circuit board and the current draw from an extra fan may blow the fuse.
TDD
That looks like something I tried to build once, but then I ran out of hot glue and gave up.
Jon
That was my thought "red-neck" it and wire into the 120 line that runs the furnace when teh relay kicks on. Seriously doubt it would be code compliant.
Harry K
Sam Takoy wrote in news:id12rp$qqe$ snipped-for-privacy@news.eternal- september.org:
I have a line voltage, 120 volts, thermostat in my poolroom. It is for heating only. Thermostat turns on a fan. Airflow thru an inline heater causes heat to come on only when fan is running. Anyway, what you need is called a line voltage thermostat. They are common and cheap.
Sam Takoy wrote in news:id12rp$qqe$ snipped-for-privacy@news.eternal- september.org:
I have a line voltage, 120 volts, thermostat in my poolroom. It is for heating only. Thermostat turns on a fan. Airflow thru an inline heater causes heat to come on only when fan is running. Anyway, what you need is called a line voltage thermostat. They are common and cheap.
Sam Takoy wrote in news:id12rp$qqe$ snipped-for-privacy@news.eternal- september.org:
I have a line voltage, 120 volts, thermostat in my poolroom. It is for heating only. Thermostat turns on a fan. Airflow thru an inline heater causes heat to come on only when fan is running. Anyway, what you need is called a line voltage thermostat. They are common and cheap.
I put a 120V duct fan in one heating duct in my old house. I hooked it up to the furnace fan controller in parallel with furnace fan . When the furnace fan came on the duct fan came on.
LdB
there is at least one gottcha with this plan if you have a multi-speed furnace blower.
The extra outlet will have 120V when the speed tap that you connect to is energized. But if your furnace at some time sets a different blower speed the exra outlet will have more or less then 120V.
If you wired the outlet to the low speed winding for example, you'll get 120V when the blower is runing low speed. But when the blower is running high speed you'll get more then 120 V which could be dangerous to your fan.
I think if you wire to the high speed winding, then the voltage will always be 120V or less which is probably safe. Moral of the story, check the voltage at your extra outlet at ALL the speeds that the blower might operate.
Mark
The speed of a furnace blower with a conventional multi-winding AC motor is not controlled by the voltage. The speed is determined by which winding is energized. There are usually three speeds available via different taps. Low, medium and high with only two connected to the control board at one time. The speed for AC is usually higher than the speed for heating.
TDD
That's funny, I have that same schematic sitting on my bench----
That was my thought "red-neck" it and wire into the 120 line that runs the furnace when teh relay kicks on. Seriously doubt it would be code compliant.
Harry K
No need to "red neck" it. There is no reason that the relay that powers the pump on a hydronic system, couldn't feed an outlet, or install another switching relay that is indirectly controlled by the same thermostat
That was my first thought too - but that darn stator acts as a transformer, perhaps? Never tried it, and I don't have a 2 speeder around to check with any more.
On my old furnace, though, the low speed was ALWAYS connected and powered - and the high speed just overtook it when powered up. Never had a problem in over 12 years running it that way (low speed never "open circuit"
It would not likely be up to code to install it in a wall box, but if it's in an electrical box (or any other metal box) that plugs into an outlet and allows the fan to be plugged into this metal box, it should be fine.
Just get a metal box, a cord wit hplug on the end, and install a thermostat transformer, relay whose input matches this transformer, and put an AC outlet in the same box to plug fan into. Then run a thermostat wire to this box. Just use a separate thernostat, not the one for your furnace.
I could design this in minutes, the wiring is pretty simple.
Google up a wiring diagram for a thermostat, then add a relay where the furnace would normally connect. The output of the relay supplies the positive voltage to the fan, the neutral is common.
If you connect the external fan to one of the motor speed leads and the furnace changes to a different fan speed, your connection won't be 120V.
If there is a DPDT fan relay and ordinary multispeed AC motor there is probably a point in the circuit that will work. Single speed motors are easier. I might hard-wire a duct fan, but for a receptacle I would use an isolating relay. Direct wiring a receptacle compromises the reliability of the furnace.
If you use a relay in a low voltage thermostat circuit, a different point is used for heating and cooling. If you tap the white wire for heating some thermostats may need to have the "heat anticipator" setting changed.
Just tripped over this at home depot. Wonder if one could cut a hole in the plastic and adjust the thermostat? Or maybe it's not adjustable.
definitely going to be a non-adjustable unit. Likely a solid state chip switching a triac.
Don't know why I bother... If you'd read the link, you'd know it's not a triac.
I saw a reference to a bi-metallic switch UL listed for
100,000 cycles.TDD
OK, I looked down the specs a bit farther - my bad - it's not electronic - just a simple bimet thermostat - but my "good luck" still holds - and any adjustment, if possible at all, would be "hit and miss". Lots of better solutions available.
The same supplier has the Duct-Stat
And ONLY $25.00. It's only good for 5 amps, not 15,
Find the blower contactor for yuor heater and get an apprpriately rated relay and wire the coil in paralell with the coil on the blower contactor. Wire normally open contacts in series with the outlet you want to control. I did pretty much the same with a helper fan. BTW Helper fan didnt work out very well, made the cold bedroom warm but made another warm bedroom cold.. Proper ducts and equalizing fixed the problem.
Jimmie
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