How to humidify only when heating

[mitchella]

I have a gas forced air furnace circa 1992 Carrier. Currently the Aprilaire 760 can come on whenever the fan is running, but I keep the fan on 24/7. I want to humidify only when actually heating. I was going to use a 24vac relay and trigger it with the heat wire (I can't remember, but after looking at the schematic I think it was the C and R terminal). so when the thermostat called for heat, the humidifier could come on. I would just switch the humidistat wire or power to the humidifer off the relay. BUT BUT BUT BUT BUT Then I saw about the current sensing relays, and wondered if this would be easier but not to sense the blower, rather to sense the "call for heat" condition. What does yu'all think??

[Ed Imeduc]

What all do you have there???? if you run the blower 24/7 that A50 wont work. Like you said you might put a 24V relay down there by the gas valve. Get the Common right there and also tie to the W there. This way fan or no fan the humidifier will come on when the burner is on and the humidistat calls for it. Dont get the power from up at the tstat you have it all right down there by the gas valve.

ED ;)

[mitchella]

Well, yes there was some rewiring done at time of install. A jumper was cut to allow the low fan (heat) speed to be on all the time unless cool was called for, at which time the hi speed kicked in. There is a switch so that it can be in regular factory mode, which I don't like. I like the low speed on full time in the summer, only kicking up for cooling. In the winter, it is always on low speed, just the burners come on and off. I think most people don't know about this simple modifacation, sort of like an orginal two speed system.

So, since the fan is on full time, I wanted to humidify only when the burners were on. I guess it is OK to have the humidifier run whenever it wants to even with the cool air, but I was concerned about concensation in the ducts, and think not much water is absorbed at room temps anyway, so most of the water went down the drain. Any thoughts?

[Ed Imeduc]

Put the relay on at the gas valve there. Then the humidifier can come on only when the burners are the hum-tstat say to .Then you can do what you want with the blower. Sounds like you should get a V/S blower in there.

ED ;)

[mitchella]

When you say hooked to the gas valve, is the best way to do that literally piggy back off the valve's main burner wires or what?

Retrofitting a variable speed blower would be cool. Is it possible and/or worth it? The current set up is a simple control board with low or high speed output to a 1/3 hp 1075rpm fasco 48 frame 3spd.

BUT BEFORE I GET AHEAD OF MYSELF, am I correct to prefer humidifying only in burner-on mode rather than full time with cool air? Thanks

[okl62]

>>BUT BEFORE I GET AHEAD OF MYSELF, am I correct to prefer humidifying >>only in burner-on mode rather than full time with cool air? Thanks

If your humidifier produces enough humidity in heat-only mode it just fine to do your change so humidifier will run only when the burner is on.

Would you please describe the way you set up one-speed fan to work on low-high speed. can you post (or send private message) with instructions how to do this? Hoe do you turn off fan completely if you need (from thermostat or separate switch)?

Thank you

[mitchella]

As I understand the wiring for conventional 2 speed setups, the heat fan relay is normally closed/on, but is turned off by the powered up furnace unless heat is called for...There is a thin metal link provided at the bottom of the circuit board where all the thermostat wires connect. Putting a simple single pole single throw switch in place of this link allows you to switch between the normal factory mode, which is thermo calling for heat on brings up the low speed, but cool or thermostat "on" brings up high speed. But if you leave that link open, then the low speed is on all the time, even though the thermostat isn't calling for anything, and then thermo calls for heat which kicks on the burners. Placing the thermo in cool kicks in the cooling fan relay and high speed as usual. \\

Perhaps some of the pros more familiar with different systems can comment. Mine is an older carrier.

[Ed Imeduc]

You can do the same for the blower to run on low all the time with just a relay there. Run a hot to the relay then to the slow sped on the blower wire it will run all the time Then the relay low V on the heat wire when the tstat calls for heat the burners will come on and also the fan on high when its time for the fan to turn on. Draw it out on paper first.

ED ;)

[mitchella]

Mine being a 2 speed furnace, I still don't quite understand what powers the relay's trigger, but I do get the use of a hot to the motor's low speed. Would the furnace's heat-on low voltage turn off the relay and allow the control board to take over and power the fan motor as usual?

If this were a 1 speed furnace, Could you be a bit more detailed? Is this setup for an otherwise 1 speed furnace with a multispeed motor? I seems so, then what is wired to the relay's low voltage trigger? And how do you keep it in low speed for heating and not allow the regular high speed to kick on?

[Ed Imeduc]

lots of ifs you have to draw it out. So out of the box here. Its all in how you want to work it. So a 24V coil or a 110V coil in the relay. Out of it SPNO-SPNC . The NC would go to the blower for slow speed all the time. Now what every you have there that works the blower for heat, fan limit ,board?? would work the relay. So when you call for heat that relay will turn the fan on to high are what you have it set on some motors have 3,4, and 5 speeds.
Draw it out first on paper.

ED ;)