Let me brag a little...

[Whitespider]

…about my furnace built from the Pacific Energy stove.

First a quick description of how the old dragon was plumbed. I use the gas furnace blower to move air through the furnace. The old Dragon was fed into the bottom by a 4” duct coming off the gas furnace plenum (positive pressure side), and a 7” “heat” duct ran from the dragon to the gas furnace cold air return (negative pressure side). So the heat from the wood furnace was mixed with the cold air returning into the system… and a portion of the “mixed” air was always “recycled” back through the wood furnace. Basically, the wood furnace was placed midway inline of a bypass damper system, and a heat sensor started the gas furnace blower. In this type of system the air is both pushed and pulled through the wood furnace, and all air passes through a single filter.

When I built the new one I decided to improve that system a bit. I brought a 6” duct off the gas furnace plenum (positive pressure side) and split it into three 4” inlets on the bottom of the new wood furnace. There’s a manual damper in the 6” duct so I can limit the amount of air feeding the wood furnace, or even shut it off completely when not in use. I installed an 8” “heat” duct off the top of the wood furnace planning to connect it back into the gas furnace plenum on the positive pressure side above the 4” “feeder” duct (rather than the cold air return) using plenum splitters to create positive and negative pressures. Well, the thing is, I hadn’t gotten around to pulling the gas furnace plenum apart and building the splitters yet… so for the time being I plumbed the 8” heat duct into the cold air return… and I think I’ll leave it that way ‘cause it’s working fantastic, the air from my heat ducts rivals that from the gas furnace.

It’s been a bit chilly in the mornings and I’ve been using the new furnace build (28[sup]o[/sup] this morning), and it makes some serious heat… the air coming from my upstairs registers is really warm during the peak of the burn. This got me thinking if I could automatically step the blower speed up a notch as the plenum air temp increased I could maximize the heat output. So I built a 24v thermistor (open below 95[sup]o[/sup], closed above) and installed it in the gas furnace plenum. It’s wired into the furnace thermostat connections using what would normally be the command to start the blower for a central A/C unit (which I don’t have)… then wired a jumper between the heat and A/C blower taps on the control board (so heat and A/C commands use the same blower speed).

This is how the system works…

1. A 110v snap switch starts the blower on low speed (via the continuous blower tap on the gas furnace control board) when the temp reaches 110[sup]o[/sup] inside the box mounted on the flue pipe.
2. Air begins moving from the positive pressure side of the gas furnace, through the wood furnace, and into the negative pressure side of the gas furnace, where it mixes with the cold air returning from the living space… and forced back into the living space.
3. When the wood furnace comes up to full temp and the “mixed” air inside the gas furnace plenum reaches 95[sup]o[/sup] the thermistor closes causing the blower to kicks up one speed, via thermostat connections on the gas furnace control board.
4. As the fire burns down, and the “mixed” air drops below 95[sup]o[/sup], the thermistor opens and the blower returns to low speed.
5. And finally, when the air inside the box mounted on the flue drops below 90[sup]o[/sup] the blower stops.
6. If at any time we want or need the gas furnace to run (I have it set to run if the living space drops to 62[sup]o[/sup]) it will override the blower commands from the wood furnace.

I’m a friggin’ genius!!! :hmm3grin2orange:

 

[Whitespider]

What? No comments on my brilliance?

 

[CWME]

:love1: <--- This what your looking for?

 

[Whitespider]

L.O.L. Now that's more like it!!!

 

[Arbonaut]

I missed how you were able to keep the gas igniter from coming on right before the fan does you might want to look in there and make sure it's not glowing. That's good with the two speed fan. If you put in a central air unit, you might be able to power that up a similar way with the EAC port, if you don't have that kind of filter running off that connection now.

 

[atlarge54]

In my world bragging is often followed by DISASTER!!!!!

 

[Whitespider]

Huh? Igniter?

The only way the gas igniter fires is if the thermostat "W" terminal at the control board receives a 24v AC signal, and the only way that can happen is if the thermostat upstairs sees 62[sup]o[/sup] or lower. Note: the 24v feed comes from the thermostat "R" terminal at the control board (sometimes "RH" and/or "RC").
The blower has three speeds, I don't use the "high" speed. Low speed is run from the "continuous" 120v blower tap (connection), it has 120v anytime no other blower tap does.
When the control board "W" terminal receives the 24v signal the 120v blower voltage is transferred to the "Heat" blower tap, and when the thermostat "G" terminal at the control board receives a 24v AC signal the 120v blower voltage is transferred to the "A/C" blower tap. The control board has an order of priority for blower voltage (independent of the gas igniter) so no two blower speeds are active at any time. High priority is the "A/C" blower speed, next is the "Heat" speed, and last is the "continuous" speed. This is all accomplished by relays, and because of the way they're laid out it's impossible for any more than one blower speed tap to have power, even if only part of the system fails... all pretty standard stuff in any gas furnace control board.
The blower motor has 4 wires, one is common and the other three each (alone) determine blower speed. Because the blower taps are prioritized you can jumper any number of the taps together, as long as you only connect a single blower wire to that jumpered circuit... if you connect two blower wires you'll burn-out the motor.
I jumpered the "A/C" and "Heat" blower speed taps and connected the mid-speed wire of the blower to it (high speed is normally reserved for actual air conditioning). I connected the thermistor to the thermostat "G" terminal at the control board, the wire coming from the upstairs wall thermostat is still connected to the "W" terminal as it always has been. My jumper simply allows both the "A/C" and "Heat" commands to share a common blower speed, independent of the igniter. Because I don't have a central air conditioner the "A/C" command is used only as a blower speed command (via the thermistor rather than the wall thermostat). Note: the "Y" terminal is used to fire the A/C compressor (usually just a "dummy" terminal used to connect the 24v "Y" wire coming from the wall thermostat to the "Y" wire going to the A/C compressor relay).

Oh... and there's one other thermostat terminal at the control board, normally labeled "T", it's a 24v common often used as the connection point for the "common" return wire from the A/C compressor relay.

 

[flyboy553]

You lost me right after "quick description of how the old dragon was plumbed.". I wouldn't know if you were dazzling me with bull poop or you are actually that brilliant! :msp_unsure:

So,in case you were dazzling me with bs, I say, yeah right!

If you really ARE that brilliant, I say, wow! good job there, Spidey!

You obviously know more about electricity and furnaces than I do!!

Ted

 

[J1m]

What? No comments on my brilliance?

Isn't there a rule around here? Pics or it didn't happen?

I know you showed general pics of the furnace in your other thread, but a knuckle dragger like me woulda had a better idea what you actually did if you showed it in excruciating detail!

 

[Toxic2]

i dont know a single thing about furnaces other than it was the first thing i ripped out of my house when i bought it.. It does sound impressive tho!

 

[darkbyrd]

What? No comments on my brilliance?

Speechless! :msp_thumbsup:

 

[owbguy]

well, this cold snap should be fuel for your gloating. :msp_tongue:

meanwhile, i'm probably losing most of my cherry crop :bang:

 

[Whitespider]

...a knuckle dragger like me woulda had a better idea what you actually did if you showed it in excruciating detail!

Hmmmm.... yeah, that would have to be excruciating... loading all those step-by-step pictures...
OK, I've thought about it... and... nope, not gonna' do it. :hmm3grin2orange:
You'll just haf'ta take my word for it... or not. :msp_tongue:

 

[J1m]

Hmmmm.... yeah, that would have to be excruciating... loading all those step-by-step pictures...
OK, I've thought about it... and... nope, not gonna' do it. :hmm3grin2orange:
You'll just haf'ta take my word for it... or not. :msp_tongue:

Fail!