Yet another OWB thermostat question

[nparch726]

Sorry guys, I've been doing a lot of reading on other threads but still can't quite get this right in my head.

I got 2 new thermostats to use on my system, the existing one was such a PITA to program I just replaced it.

OK, so thermostat #1 (which should run the existing gas furnace) has 4 wires coming into it, Red, Yellow, White, and Green. Thermostat #2 (which should basically just allow the fan to run without firing the gas furnace) is a heat-only thermostat with just 2 wires running from thermostat #1, Green wire on #1 to the White terminal on #2, and Red on #1 to Red on #2.

I got this wiring setup directly from the Central Boiler website and instruction manual, got it all hooked up the other day just how they explained it. I don't have the OWB quite ready yet so I went to fire up the gas furnace just to test it and make sure it was going to work and serve as the backup eventually. Well, when it took off it seemed to work, but the A/C unit also came on, which definately threw me off. So I guess that's my first question, what did I mess up there and can I make it work how I have it set up without a bunch more wiring or extra relays?

OK so here's my next dilemna, while trying to just run the gas furnace, I left thermostat #2 in the OFF position and tried to run the furnace with just thermostat #1. Not much luck there, the blower wouldn't come on, so I turned thermostat #2 on and dialed the temp up on it, which allowed the gas furnace to operate normally, except the blower kept running after it quit firing on gas since the temp setting on #2 was a bit higher than #1. Once again, is there something I messed up here, or is there a way to operate the system with just the one thermostat?

Sorry if I sound like a complete bonehead here guys, the mechanical part of this whole OWB setup has been real easy for me, but this whole thermostat thing is driving me nuts. I think I can make it work, I just want to make sure it is working as it should, and of course safely, thanks for any input guys!

 

[Windwalker7]

I was in the same boat as you when I installed mine last year.

I ended up hiring a HVAC guy to come hook up the thermostats. Hated to do it but I couldn't figure it out.

Here, I needed a relay hooked up to the existing furnace.

I had to pay the guy about $350 for labor and parts. I probably got ripped off, but every thing else was ready to go except the thermostat. It was almost November and I was anxious to see how well it would heat the house.

 

[NC4AB]

It sounds like you have it wired correctly, but I will repeat everything for my benefit:

Existing thermostat # 1 wiring is:

Red 24 VAC Hot
Yellow Compressor enable (A/C)
White Heating
Green Blower Fan

You need to jump the following wires from # 1 to # 2

Red to Red (24 VAC Hot)
Green #1 to White # 2 (Heating)

This will work provided that Thermostat # 1 has a "fan only" position. You might want to find the manual for you gas furnace, as some control the fan independent of the thermostat.

Trouble shooting:

Check and make sure you don't have any wires making contact on the wrong terminals

Un-hook Thermostat # 2 and see if everything works normally (which it should).

If this works connect everything back up and try using Thermostat #2 with #1 turned off and see what happens

If all else fails you can install a programmable thermostat ( I used the Honeywell TH8320 series) that does everything in one thermostat

 

[Butch(OH)]

Realize that advise from me is not coming from a HVAC expert, or even an HVAC novice, but HVAC ignorant. I can however read a meter and wire up my model 1938 tractors so the magnetos and headlights work without short circuiting and did manage to get my OWB controls working without any relays or complicated wiring.

As far as I can tell from my reading here and in listening to a local HVAC guy who struggled to get a similar system up and going the problem lies with trying to run the fan with what amounts to two thermostats operating in a parallel circuit to the furnace controller. No matter if you have a simple heating system or a complicated one such wiring can cause back feeds, burns up expensive circuit boards and/or fire up the AC units while you are trying to heat the house. I solved that problem in my installation by simply wiring the second (OWB) thermostat in series with my original thermostat.

Now realize that my original home heating is a simple single stage 90% eff gas furnace and that is a far cry from a system with 2 or 3 stage heating, heat pumps, geothermal loops and the various back up systems that such new generation heating requires. Such systems are going to require some fancy control wiring best done by a pro. You need to also realize that here is two operating systems for even the basic type gas forced air heating equipment like I have. In one type the thermostat only controls the burner and when the heat exchanger heats up to "X" temp a separate switching devise turns on the fan and blows warm air into your house. The other type (which I own) there is only a "smart box" basically a timer in the furnace. When my thermostat calls for heat the furnace lights and in a given time setting the blower kicks on. Not sure if it makes any difference in adapting for a OWB but like I said I am no HVAC 'spert.

All that being said and with proper caution and safety gear, rubber gloves and safety glasses on here is how I wired mine. MY original thermostat has a "Fan ON" switch that will run the fan anytime. Furnace on, AC on or both turned off that switch would run the fan and I thought "all I need to do is operate that switch automatically". In checking out how it worked with a meter and following the wires I found that it simply connected two terminals on the furnace controller. I think, repeat THINK it is the "R" and "G". This can be checked out with a search here or punch in google "standard home forced air furnace control wiring" or similar. Anyway if your thermostat is similar you don't need to know what it hooks to downstairs anyway. You remove the cover from the thermostat and you will find that here is two wires on the "fan" on switch. You cut one of the wires and attach a wire to each end long enough to reach your second thermostat and attach them to the proper terminals. In other words once you are done with the wirng in your old thermosat and before you attch them to your new thermosat you could twist the wires together and the fan would run, am I being clear enough here? This is what I mean by a "series" circuit. I cannot remember the thermosat terminals but they are simply found by reading the instructions that come with the new thermostat. I did double check with a meter while playing with the temp adjustment before I wired it in (that smart box on furnaces is expensive!). When we have the OWB lit and up to temp we switch the fan on switch to "ON" and the second thermostat then controls the fan. Hope I made sense of it, it took me less time to wire it than to type this, LOL.

 

[Butch(OH)]

It sounds like you have it wired correctly, but I will repeat everything for my benefit:

Existing thermostat # 1 wiring is:

Red 24 VAC Hot
Yellow Compressor enable (A/C)
White Heating
Green Blower Fan

You need to jump the following wires from # 1 to # 2

Red to Red (24 VAC Hot)
Green #1 to White # 2 (Heating)

This will work provided that Thermostat # 1 has a "fan only" position. You might want to find the manual for you gas furnace, as some control the fan independent of the thermostat.

Trouble shooting:

Check and make sure you don't have any wires making contact on the wrong terminals

Un-hook Thermostat # 2 and see if everything works normally (which it should).

If this works connect everything back up and try using Thermostat #2 with #1 turned off and see what happens

If all else fails you can install a programmable thermostat ( I used the Honeywell TH8320 series) that does everything in one thermostat

Sorry about stepping on you a bit, you posted while i was typing my long winded answer, LOL

 

[Slick]

THat's how I did it also...my original gas stat has the fan set to auto so it run my AC and gas furnace as it always has but it also had a dedicated fan wire that I could turn the fan on any time I wanted to circulate air....I just disconnected it from the original stat and hooked it to the heat output of the owb stat...that's all...

 

[nparch726]

Thanks for the replies guys!

Thanks guys, I came home from work today and read up on what you said, I didn't change anything but thought I'd try it again and by some miracle hope it worked.

I have a super simple furnace just like Butch mentioned, just a 90% eff. standard Frigidaire gas furnace. I just bought the house in the last year or so, so I'm not terribly familiar with it, but easy system nonetheless. So here's how I thought it was supposed to work, I thought when the thermostat called for heat, the blower came on, then the gas fired after the blower was already running.

Call me a bonehead if you want, but after a bit more investigating I figured out the gas fires, and after a certain time or temp comes, then the blower comes on. I was just scared the other day when I first tried to start it up when the gas fired without the blower going, that just didn't seem right to me at the time, I just wasn't patient enough to let the blower come on because I thought I had a problem with the gas firing when it shouldn't have been.

Butch, is there a way I can wire this in series as you said using the existing terminals rather than cutting into one of the fan wires? Not to sound like a bonehead, I work on high voltage transmission and distribution lines every day, but I'm not always that good with control circuits like this.

 

[Butch(OH)]

Butch, is there a way I can wire this in series as you said using the existing terminals rather than cutting into one of the fan wires? Not to sound like a bonehead, I work on high voltage transmission and distribution lines every day, but I'm not always that good with control circuits like this.

I tried fourteen times to type up something that explained it better and each time after it gets about a page and a half long and its so wordy that even I get confused. Try this one.

No you cannot simply screw some wires to a terminal and do what you need to do. In my uneducated opinion this is what gets people into troubles like the AC running when it shouldn't and burning up controllers. That is not HVAC knowledge speaking there, just opinion based upon the fact you cant have two controllers trying to operate the fan at the same time no more than you and your wife can both have hands on the steering wheel of your car and stay out of the ditch.


The fan on switch does one of two things two things. Let the furnace controller operate the fan, (when set to fan auto) or simply turns the fan on and leaves it on (when set to fan on) What we are doing is "fooling" the furnace controller (for lack of a better term) into thinking the fan is on but in reality it is either off or on depnding on the setting of thermostat 2 and the room temp. The reason the gas furnace will still start and run is the burner is independent of the fan OK? Even when the fan is switched ON, the furnace can be set to X temp with the original stat and the burner will cycle to keep the room at the set temp, staying with me here?? This is what the controller THINKS is going on when we leave the fan on switch to ON but we threw it a curve ball by placing a second stat in the fan on circuit IN SERIES. Now with stat 1 (gas furnace stat) set a few degrees lower than stat 2 (the OWB stat) the blower will run when stat 2 calls for heat, the burner wont run because it is being controlled by stat 1 just like it has for years, still with me?? Now lets assume the house is calling for heat and the blower is running but the OWB gets low on wood. Neither thermostat, 1 or 2 has a clue what is going on in your back yard. The fan comes on with stat 2 and stays on but with the OWB temp down it cant keep up with demand so the room temp keeps on dropping until it reaches the set point of stat 1. Then the burner comes on to keep the room at that temp. The fan will run continuously and not cycle because stat 2 is telling it to run. That is the only drawback to being wired in this manner and aminor inconvience IMO. Complicating the system with some sort of temp robe in the lOWB loop that cuts out at X temp would solve that too.

Hope I have not confused further here/

 

[RacerX]

What is the purpose of stat #2? Is it only to turn on the fan when the temperature reaches a certain level and keep it on until the temperature drops below that level?

 

[Slick]

Yes, stat 2 (the OWB stat) only turns the fan on...but you have hot water circulating through your heat exchanger which is sitting in the ductwork and hot....so by turning the fan on your blowing how air through the house. In a normal situation meaning your OWB water temp stays up, fire doesn't go out etc...this is all that will ever happen all winter....fan will go on and off from stat 2 and all will be good....the rest of the explanation is to explain what happens if your fire goes out, the fan blowing does not heat the house (water temp is to cold) and your stat 1 then kicks on because it's set a few degrees lower, that's when your gas burner etc kicks on.