Full thermostatic control for wood furnace-would this work?

[Badfish740]

Managing comfortable temperatures in our small ranch with the Englander 28-3500 has always been a challenge. It's pretty easy to cook ourselves out of the house-especially at night when trying to strike the balance between an all-night burn and a reasonable bedroom temperature. I'm currently working toward completely redoing the ductwork in the house for this as well as a variety of other reasons, and I've come up with an idea for attempting to regulate the heat output (or at least the heat input to the house) from the Englander via a thermostat. Here goes:

A thermostat would be mounted on the wall next to the thermostat controlling the oil furnace. Just a simple, non-programmable one. Instead of controlling the blower on the Englander, the thermostat would control a power actuated damper like this one, which would be mounted inline with the duct delivering hot air from the Englander to my oil furnace plenum:

(broken image removed)

http://www.mcmaster.com/#2041k12/=umdicd

The thermostat and blower on the Englander would remain intact and operate completely independent of the power actuated damper. Operation would be as follows:

The Englander would operate as normal with the thermostat mounted on the back of the furnace controlling when the blower kicks on and off based on the temperature of the air jacket around the firebox (ie: on at 220 degrees/off at 190 degrees or thereabouts). The difference will be what happens with the heated air once it leaves the top of the furnace and enters the ductwork. If there is a call for heat from the upstairs thermostat, the actuated damper would be closed so that the heated air from the Englander enters the ductwork in the house, raising the air temperature. Once the setpoint has been reached, the damper would then open, dumping the heat into the basement until there's once again a call for heat, at which point the damper would close. I'm hoping that this will accomplish a few things:

• Make regulating the upstairs temperature easier (ie: Being able to keep the house at 70-72 degrees reliably).
• Provide a little extra warmth for the marginally insulated finished basement in the wintertime.
• Allow the Englander to run wide open-more efficiently and cleanly more often.
• Keep oil heat usage to a minimum during the shoulder season.

Now a few words about safety-from what I'm reading of these dampers they are spring loaded so that they can be set to be normally open or normally closed. I would set mine to normally open so that if the power goes out or the actuator is de-energized for any reason, that it will default to open and the heat would dump into the basement in a safe manner. Finally, it would also be wired so that the Englander and the oil furnace/AC unit cannot be on at the same time. It all sounds good in my head, but I want to run it by others here who are more knowledgeable.

 

[Badfish740]

On second thought this one is cheaper and should be easier to integrate. It has a spring return:

(broken link removed)

 

[laynes69]

Either way heat will enter your house, whether from the jacket in your woodfurnace, or thru the ductwork. If that basement gets hot, the heat will enter the living space above. It sounds like your woodfurnace is oversized. Could you just close the bedroom duct to allow less heat? As far as regulating the home temp, maybe smaller fires?

 

[brenndatomu]

Sounds reasonable to me. As long as the basement isn't too well insulated, it will absorb quite a bit of heat. Just ask someone who is trying to heat the whole house from a free standing stove in a un-insulated basement, it doesn't work too well often times!
Having warm floors will be a nice side benefit for you too.
Like Laynes said small, quick, but hot fires are the key to regulating the BTUs coming off what sounds to be an over-sized furnace for your house. Input = output as they say

 

[STIHLY DAN]

I think that will work great. Shoulder seasons are tough with a furnace. Many people have a stove for shoulder, and furnace for winter. I hope to be one of them soon. You could put balancing dampers in your take offs. That way you can control what percent of heat goes where. I can adjust the flow to any rm in the house from the basement. It will take a week or so to get it dialed in perfect.

 

[Badfish740]

Either way heat will enter your house, whether from the jacket in your woodfurnace, or thru the ductwork. If that basement gets hot, the heat will enter the living space above. It sounds like your woodfurnace is oversized.

Sure, I understand that the heat is going to get in somehow, but it won't be the same as having it blowing directly into the room. Also, as brenndatomu pointed out, the basement is not going to retain a lot of the heat-only some of it is going to rise through the floor, which, as he also states, gives a nice "poor mans radiant floor heat" effect When we were out of power for eight days after Sandy, I disconnected the furnace from the ductwork and just let it dump heat into the basement and though the house did not get as warm as usual, the wood floors felt very nice on our feet. Our house is definitely too small for the 28-3500, but I got it used for $300 six years ago from a member here when I didn't know nearly as much as I do now. Now I'm just trying to work with what I have and make it a little more "wife friendly."

Could you just close the bedroom duct to allow less heat? As far as regulating the home temp, maybe smaller fires?

This gets to the "wife friendly" part. What ends up happening is I close off the bedroom duct (there's a damper in the take off in the basement) at night when there's a fire in the furnace. Inevitably I forget, the house cools off during the day, my wife turns on the oil heat before I get home, and then calls me because the bedroom is cold even though the oil furnace is cranking... I'm looking for a more elegant solution basically. As for the quick, hot fires, they are great, but the insulation is the house is such that the heat generated dissipates fairly quickly. I'm hoping that the basement dump/thermostat idea evens things out.

 

[Badfish740]

Ok-I was able to pick the brains of some HVAC pros on a hunting forum I frequent and came up with the following-here is an overview of what the system will look like:

All I will need is a simple thermostat and a 24VAC transformer. The transformer will be wired to both dampers with the thermostat acting as the switch. When the house temp is lower than the setpoint, the switch will close, completing the circuit, and sending power to both dampers:

When the setpoint has been reached, the switch will open, de-energizing the spring loaded dampers, which will return to their normal positions:

I'll hopefully have the time to tear everything apart and re-do it between Christmas and New Years just in time for the really cold weather. Looking forward to posting my results.

 

[sloeffle]

I pretty much have the same exact setup that you have except that I use 24V powered Honeywell dampers. I have a 24 x 24 zoning normally open damper on top of the geo furnace that closes when the wood furnace comes. I also have a normally open ( during the winter ) round zoning damper between the wood furnace plenum and house ducting that closes when the geo comes on.

Wired up a 24VC AC transformer that gets energized when the fan on the wood burning furnace comes on. I would recommend driving the dampers off of the fan on the wood furnace. In my case, the thermostat temperature could be reached but the plenum temperature could reach 150F which would cause the fan to kick in.

 

[Badfish740]

For those who are interested, I was able to hook up with an HVAC pro over on another forum who sent me this diagram, which shows how to wire two dampers to be controlled by a thermostat:

By putting the thermostat right outside our bedroom I should be able to keep that part of the house cool enough for sleeping even with the furnace really cooking. The heat will get diverted to the other side of the house, making the basement family room and kitchen floor (directly above) nice and toasty.

 

[NE WOOD BURNER]

Well that's a large firebox.

Just a thought: by adding more fire brick you could reduce the firebox volume. BTUs in equals BTUs out. control intake air to get a more controllable fire.