Welcome, Guest. Please login or register.
Did you miss your activation email?

Username: Password:

Author Topic: Single Thermostat for wood boiler and furnace  (Read 4092 times)

gmviso

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
  • OWF Brand: Central Boiler
  • OWF Model: CL5036
  • Northeast Indiana
    • View Profile
Single Thermostat for wood boiler and furnace
« on: November 23, 2011, 08:32:11 AM »

So, I researched this subject like crazy on this forum and across the web and never found an answer that I was satisfied with, so last night I tried what I am about to share and it appears to work to my satisfaction.

System Requirements:
1) 2 stage thermostat. A heat pump thermostat is not a 2 stage thermostat. What I have is an Ecobee EB-STAT-02, so it is the onlly one I have tried this with, but I am sure other manufacturers have programmable digital thermostats that will work as well. The Honeywell IAQ and Prestige are examples.

2) 3-way zone valve

3) 120VAC to 24VAC 40VA step down transformer. This can be a Hard-Wired type, or a Plug-In type.
INSTALLATION STEPS
(i will upload a drawing later)

1) Install 3-way zone valve between Input and output of Water/Air heat exchanger as follows.
    A) Hot from boiler (or DHWHX out) to 3-way zone valve COMMON.
    B) 3-way Zone Valve NC (Normally Closed) to Water/Air Heat Exchanger IN.
    C) 3-way Zone Valve NO (Normally Open) to one side of plumbing Tee.
    D) Water/Air Heat Exchanger OUT to second side of plumbing Tee.
    E) Third side of plumbing Tee RETURN to Boiler.

2) Electrical Hookup
    A) 24VAC terminal 1 to 3-way Zone Valve terminal TH
    B) 24VAC terminal 2 to Thermostat RH. (If there is a jumper on thermostat between RH and RC leave it in place)
    C) 3-way Zone Valve terminal TR to Thermostat terminal W1 (may be labeled W O/B). If this is an existing installation your furnace W terminal is probably connected here. Move it to Thermostat terminal W2.
    D) If you haven't already done so in (C) above, connect Furnace terminal W to Thermostat terminal W2.

That should do it. The way this is going to work is:

Thermostat will call for heat, energizing the solenoid in the 3-way zone valve thus allowing hot water to flow through heat exchanger and turning on the furnace fan. If after a preset amount of time (my thermostat seems to be set for about 10 minutes) if the room temp has not risen sufficiently the furnace burner will start. My thermostat also keeps the zone valve open so the boiler is still helping to heat. I haven't tried this in practice yet, but I have to believe that with the water temp being 165 or so, the likelyhood of the furnace burner lighting is small.

By the way, if your thermostat is already controlling and wired for one of the new 2 stage furnaces you are just going to have to try this or ask an HVAC professional.
Logged
Central Boiler CL5036

yoderheating

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 802
    • View Profile
Re: Single Thermostat for wood boiler and furnace
« Reply #1 on: November 23, 2011, 08:49:27 AM »

 It sounds like you may have a gas furnace?
Logged
Southwest Virginia
WF4000 Heat Master

gmviso

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
  • OWF Brand: Central Boiler
  • OWF Model: CL5036
  • Northeast Indiana
    • View Profile
Re: Single Thermostat for wood boiler and furnace
« Reply #2 on: November 23, 2011, 09:34:56 AM »

Yes, it is a gas furnace.
Logged
Central Boiler CL5036

yoderheating

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 802
    • View Profile
Re: Single Thermostat for wood boiler and furnace
« Reply #3 on: November 23, 2011, 11:26:35 AM »

That should work so long as the water coil puts off enough heat to activate the heat sensor.
Logged
Southwest Virginia
WF4000 Heat Master

gmviso

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
  • OWF Brand: Central Boiler
  • OWF Model: CL5036
  • Northeast Indiana
    • View Profile
Re: Single Thermostat for wood boiler and furnace
« Reply #4 on: November 23, 2011, 09:29:44 PM »

I finally got my new wood boiler fired up tonite.

In practice my thermostat scheme does not work as I had hoped. The smart thermostat is 'stupid'. It waits 4 minutes after starting stage 1 heat (in this case my wood boiler), and then starts stage 2 heat using my expensive propane in addition to the hot water exchanger.

For now I have disconnected stage 2.

Back to the drawing board.

Logged
Central Boiler CL5036

gmviso

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
  • OWF Brand: Central Boiler
  • OWF Model: CL5036
  • Northeast Indiana
    • View Profile
Re: Single Thermostat for wood boiler and furnace
« Reply #5 on: November 29, 2011, 03:06:50 PM »

Ok, figured out a cheap modification.

I need to acquire a 'Snap Disk Limit Switch'. Gonna get a White/Rogers 3L05-10. It is adjustable from 135 - 175 degrees F with a 20 degree differential. It is available on line from pexsupply.com for $14.45.

http://www.pexsupply.com/White-Rodgers-3L05-10-Snap-Disc-Limit-Control-135-to-175-Degrees-F-Range-20-Degree-Differential-Open-on-Rise-14765000-p

It is a normally closed SPST switch which opens when a set temp is reached and closes again when the temp falls 20 degrees below set point. I plan to set for 160 degrees.

I will attach to Air/Water heat exchanger 'Hot Water In' pipe. The switch will be wired in series between W2 out of Thermostat and Furnace Control wire.

So, when the Heat exchanger has at least 160 degree water flowing through it, the Snap Disk Limit Switch will be open, and even when the stupid thermostat tries to fire my furnace burner, it will not. But if the once the heat exchanger water input drops to 140 degrees the Snap Disk Limit Switch will close and allow the furnace burner to operate.

Hope this works for you as well.
Logged
Central Boiler CL5036

abarton

  • Newbie
  • *
  • Offline Offline
  • Posts: 33
  • OWF Brand: taylor
  • OWF Model: 450
    • View Profile
Re: Single Thermostat for wood boiler and furnace
« Reply #6 on: January 09, 2012, 05:09:15 PM »

A heat pump thermostat is a two and sometimes three stage thermostat.  It's just not designed to operate a gas furnace. I have wired many systems and most people like a standard thermostat with a toggle switch mounted out of sight to toggle between wood boiler or conventional heat
Logged
"I could have saved a fortune when I built my house if only I had not installed any light switches but instead straight wired all the lights. I'm the only one that realizes they also turn off"

donahuej

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 56
  • OWF Brand: American Royal
  • OWF Model: 7300
    • View Profile
Re: Single Thermostat for wood boiler and furnace
« Reply #7 on: January 13, 2012, 03:58:17 PM »

Guys had the same problem and have a I have a fix - you need a two stage thermo that has and adjustable differential....here is my post just a few down from this one...

http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=1179.0
Logged

gmviso

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 79
  • OWF Brand: Central Boiler
  • OWF Model: CL5036
  • Northeast Indiana
    • View Profile
Re: Single Thermostat for wood boiler and furnace
« Reply #8 on: January 13, 2012, 07:38:54 PM »

Guys had the same problem and have a I have a fix - you need a two stage thermo that has and adjustable differential....here is my post just a few down from this one...

http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=1179.0


Well, sure, if I wanted to invest in another expensive thermostat I would. My solution allowed me to keep my existing Multi-stage thermostat by adding a simple $15 thermo limit switch.
Logged
Central Boiler CL5036

rick w

  • Newbie
  • *
  • Offline Offline
  • Posts: 45
  • OWF Brand: portage&main
  • OWF Model: portage&main ml 36
    • View Profile
Re: Single Thermostat for wood boiler and furnace
« Reply #9 on: January 25, 2012, 07:55:18 PM »

 i just installed a braeburn model3200 mulit stage2 heat and 2 cool thermostat and what a difference it made.i had 2 thermostats before and could not avoid cold spots to much heat differental this thermo you can adjust the set back from 1 degree to 5 degrees i left mine set at 2 where it was set at the factory less wood being burnt and no more cold between start up and shut downi think its worth the extra money i believe i will save enough in wood to pay for it pluss the comfort is well worth it check them out on there web site thanks rick
Logged