One Thermostat or Two?

[Tennman]

I asked several weeks ago how to control two furnaces but need more advice. Do you guys have separate thermostats or one that can roll to the the second furnace if the boiler goes cold. I've researched 2-stage thermostats but I'm not sure that's what to use. Since we don't have storage, I find myself turning on the propane for 30 minutes or so in the morning to knock off the chill until I get the hot water going. I'd appreciate any help pointing me where to go.

 

[twitch]

I thought about using one to control both the boiler and hot air furnace, but just put a second t-stat in. One for the Tarm, the other for that oil furnace. I just leave the oil t-stat at 55 or so in case something goes awry with the wood boiler and I'm not home.

 

[Tennman]

Scott, That method would be fine with me and in fact preferred. But my HVAC guy only knew how to wire it up so it would work by manually turning off one thermostat and turning on the other. Our home is very remote so my problem might simply be the inexperience of my HAVC contractor. The other problem my system has is the house calls for heat and keeps the fan on even though the boiler circ pump is off. This results in blowing cold air. I think this can be solved with an aquastat. Then answer may be to just find a more knowledgeable HVAC guy. But if I had two thermostats that could both be on that would be fine.

 

[ohbie1]

You can also do an aquastat on the wood boiler(measuring water temp.) to a relay on the TT line. When the wood boiler water is hot enough it either engages or disengages (your choice) the relay which in turn sends the TT info to the propane or the wood. This would keep the house at whatever TT setting you select. If the wood boiler water is not hot enough, the aquastat tells the relay to switch over to the propane.

This assumes that you only want to direct the TT info. and that your boilers are likely hooked in series,(you didn't say) otherwise you would need some zone type valve(s) that would also divert the water through the propane OR through the wood.

 

[webie]

I vote 2,,,,,,,,,,,,,,,,you have more options .

 

[twitch]

As ohbie1 mentioned, I have an aquastat in my air handler that will not allow the TT line to activate the fan unless the temp is above the setpoint. My boiler circ pretty much runs until the boiler cools after the fire is out, but I'm working on controlling it so it will only run when the temp at the air handler is say 12 degrees or more cooler than the boiler supply. That way if there is no call for heat in the house, the pump won't run.

My system is pretty simple in that the air handler is only used with the wood boiler, and the hot air furnace is completely separate. I'm not quite sure how I'd wire it if I was using an HX in my oil furnace and using it's blower.

 

[Tennman]

I like the simplicity of two t-stats. I'm sure it would be simpler for my wife also. I don't think my HVAC guy knew how to make them work independently. More background we have a forced air Amana propane furnace, and now debugging the boiler we've been running since Nov '09. At the moment when "on" the boiler t-stat fan blows all the time regardless of the water temp coming from the boiler. I think I have two problems:

1- I need to get the t-stats so they can both be on and independently control each respective heat source.
2- I need to add the aquastat or connect to my boiler controller so the fan doesn't continue to blow when the water is not circulating.

I'm sure this is pretty simple to most HVAC guys. I'm pretty sure it means at least a relay, but I have no experience in HVAC controls. It may mean I try to find a more experienced contractor.

 

[hokiefan]

Anybody looked into using a Honeywell 8000 series thermostat, three heats and two cools capability, I bought one and hope I can use it to control my owb on one heat setting and use another to control my gas pack.

With the owb it will be set to switch the fan in my gaspack on and off as it calls for heat, my heat exchanger will be hot at all times unless I decide to use a relay to switch my taco pump on or off.

Soon to be buring wood instead of propane!

 

[webie]

Tennman check out this thread , you may find it interesting reading.
https://www.hearth.com/econtent/index.php/forums/viewthread/52532/

 

[ohbie1]

At the moment when "on" the boiler t-stat fan blows all the time regardless of the water temp coming from the boiler. I think I have two problems:

1- I need to get the t-stats so they can both be on and independently control each respective heat source.
2- I need to add the aquastat or connect to my boiler controller so the fan doesn't continue to blow when the water is not circulating.

Doesn't your TT have a switch somewhere that says " Fan - On - Auto" where you can select on or auto?
I ask because mine does, and if you select "on", the fan runs constantly.

 

[ohbie1]

1- I need to get the t-stats so they can both be on and independently control each respective heat source.

You realize that if you have 2 TTs working independntly:

If you set the propane say 5 °F below the wood, when the propane is on, the wood will also be on, because its TT is still calling for heat. Thus you WILL need a WB aquastat in line with the WB TT to have the WB not run(circ.) if its water is cold.

 

[taxidermist]

I sent you that wiring diagram of how to hook up your 2nd thermostat to your forced air furnace. Without storage it is kinda hard to always have hot water flowing when your thermostat calls for heat. You might want to run a wire above ground out to the boiler to control the pump with your thermostat. When you redo your underground add wire then to the trench.

Rob

 

[Tennman]

Thanks guys, I will check out the Hearth thread webie. Yes Obi they would both be on and they do have automatic, its beginning to look like my system is at least missing an aquastat. I'm going to go read some at these threads.

Rob did you email? I'm off today so I'm doing boiler stuff. I don't see it on my PM either. Terry has some suggestions also. Looks like I need another piece of hardware and I'm planning on digging my PEX up in the next month or so. At that time I'm going to add a sensor wire back to the boiler barn.

Appreciate the help from all.

 

[Tony H]

I am running two thermostats on a forced air furnace with an heat exchanger, A/C and humidifier . We have a couple extra relays to turn on the humidifier and keep off the A/C when the 2nd thermo that runs the boiler is on. I keep both the thermos on with the boiler set at 72 and the original gas thermo set at 65 so if the temp . The only issue is the fan will continue to run even if the boiler is cold so need to add an aquastat to shut the blower off.

 

[Tennman]

Yeah that's what I want Tony. I'm going to order an aquastat hopefully tomorrow. My HVAC guy will know what to to with relays etc. I'm going to make my current two tstat system work which I know it doable (just I don't know how, but learnin). I've been PM'd some schematics.