has anybody modified their woodstove to make it sealed combustion?

[surviverguy]

I modified my woodstove this winter to change the way it draws its air from naturaly drafted to sealed combustion. Instead of drawing air from inside the room (which creates drafts through the house) I force air from the crawlspace through piping directly into the firebox. I get more blue flames and use less wood to get the same amount of heat.

 

[pen]

Lots of people use what's called an OAK (outside air kit) to pull non-living space air into the stove.

What kind of stove did you do this for? (makes it easy if you add your stove to your signature line)

Welcome to the site

pen

 

[surviverguy]

The stove was from Northerm Handyman and was called a King woodstove. I see now that they sell the same stove but the name has changed.

 

[surviverguy]

It's now called a whistler by century. It has its air intake slots above the front door.

 

[semipro]

I I force air from the crawlspace through piping directly into the firebox..

Are you really "forcing" air into your stove?
I'd be careful. I doubt your stove is truly airtight. You could force combustion gases to exit the stove into your living space.
If you don't believe your stove leaks, plug up the flue once and toss in a couple of pieces of lit newspaper then close the door. I've done this on two different cast iron stoves and was amazed where and how much leakage occurred. Steel stoves might be better but I'll bet the gaskets still leak.

 

[surviverguy]

The 31 watt fan I'm using to force the draft isn't enough to get the fires started. I have to keep the door cracked open for the first ten minutes. The draft created by the fan is very light. The fan just helps move the cold air up and through the piping. The stack creates a good draft when the fire is burning hot and the fan can be turned off, but it seems to have better combustion of the gases (more blue flames) with the draft fan on. I turn the fan off after the fire is out.

 

[surviverguy]

I ran the stove this way all winter (2 cords) and never got any smoke in the room- except when a log (E/W) rolled forward to the door glass and I (carefully) opened the door to push the log back. I use a low rebar welded grate between the wood and the bottom firebrick. I'm going to add (weld) some rebar vertical in the front to stop logs from being able to roll forward. I hate the danger of forward tumbling burning logs and the ashes they leave inside of the door, and the smoke that comes out of the stove when I have to adjust those front logs.

 

[pen]

What's the purpose of the grate? In general, wood stoves shouldn't use them and most (if not all) manuals specifically say not too.

Also, it wasn't burning well w/out the fan? Forced induction isn't really a great idea. This stove should feed the fire way more air than necessary since it is not an EPA unit.

If it wasn't burning that great w/out the forced air, I'd say either your chimney isn't sufficiently supplying draft or more likely, the wood isn't seasoned as well as it should be.

pen

 

[Highbeam]

I use crawlspace air also for my "sealed" combustion system. I do not need to force air into the intake though, there is plenty of natural draft creating a flow from the crawl into the stove and then from the stove to the chimney cap. Click on my signature link about the OAK to see the crawlspace plumbing.

OAK in general is a great idea. Adding forced air combustion, not so good.

 

[laynes69]

The specs for the stove say full load run time of 1-2 hours, and a 110,000 btu output. I agree, I wouldn't force any air into the firebox, even if it's a small amount. Sounds like a band-aid for draft or not so par wood.

 

[DexterDay]

The specs for the stove say full load run time of 1-2 hours, and a 110,000 btu output. I agree, I wouldn't force any air into the firebox, even if it's a small amount. Sounds like a band-aid for draft or not so par wood.

Yep... As others have stated. Sounds like a band-aid to a problem.

Are you closing the air down also? If you are (I would hope you have to close the air some) then why use a fan? Why not just induce enough air to keep a hot fire/flue and that should produce sufficient draft.

How tall is your chimney? Is it a basement install? Or is it a Main floor install? Any 90° 's in the flue? Or is it straight up?

Also, when was your wood Cut/Split/Stacked? How long has it seasoned?

 

[surviverguy]

Oh yeah...there is something cooling the firebox.. .a doubled stainless steel coil 3/4" I.D. with water circulation...you see the woodstove is an indoor boiler (DIY) and it never gets too hot. The grate helps burn nice and hot to compensate for the water cooling effect. The hottest I've seen is 280 celcius at the stovetop. I never dampen the fires. In fact the damper is set up to not close down. I use short hot fires. I'm in Georgia where the heat loses generaly aren't that great. If it gets down to 20 degrees f. outside, then I'll keep adding wood, otherwise one load is usualy enough or maybe I'll toss a couple splits on top of the coals.. I let the fires go out when the living room temperature gets close to 80 degrees F. I like to keep the house in the 70's. The hot water is used for heating domestic water and for low temperature radiant floor heating. I do have lots of water storage capacity. The oak isn't seasoned two years yet....more like 1 1/2 years. I'll be burning seasoned pine also next season because I have lots of it and it burns fast and hot. The stack is 6" diameter straight up. There is a heat reclaimer with thermostatic fan about 20 inches above the stove and I try to keep the fires hot enough to keep that reclaimer fan blowing. The stove sits in a large room with an 18 foot high vaulted ceiling. The stack was pro installed and rises about two feet above the ridge of the roof. I also use another thermostaticaly controlled blower fan which blows up the back and across the top to help get heat out and away from the stove when the stove top temp is over 100 degrees celcius.

 

[Highbeam]

Uh oh, a MAGIC HEAT

 

[DexterDay]

Where are you measuring your temps? And with what are you measuring them with? And why in Celsius? ?

Do you have single wall inside (18ft inside pipe)? Or double wall inside?

That Magic heat will actually take heat from your stack and negatively affect your draft.

If your not adjusting the air and its wide open. Your only asking for an Overfire situation. IMO. And that grate is not needed for Hot fires. I can get my stove top temp well over 1,000° F (didnt mean to get it that hot) by just laying the wood on coals.
My normal temps are 700°-500° throughout most of the burn and I can get 8 hrs out of Softer wood (Pine, Silver maple, Etc).

Why not slow the fire down and have lower temps, for a longer time? Instead of high temps, for a short time??

 

[surviverguy]

What size piping is recommended for an "oak" for this type of non-EPA stove (6" exhaust) and how many bends are allowed to flow good without fan assistance? I'd guess my ("oak" intake) piping is undersized and the slight assistance from the small draft fan is helping overcome the intake restriction when the fires are getting started. The normal max burn temp of the stovetop is about 520 f. by conversion from celsius digital pid temperature controller with platinum sensor resting on top of the stove,

 

[surviverguy]

Is this heat reclaimer bad to use? I believe the piping in the room from the stove to the vaulted ceiling is single walled. It certainly puts out heat.

 

[mellow]

How much creosote are you getting when you sweep your chimney?

 

[Backwoods Savage]

Sounds like a bad nightmare to me. Perhaps good in theory but...

 

[Dune]

What kind of safety equipment did you install on your boiler? Is there a circulator? If so, how is it controlled? Do you have a dump zone?
Would your fire start without having the door open before you installed the OAK?

A force fed wood fire can easily melt steel. I am not kidding.

 

[pen]

going to move this over to the boiler room since I think its a better fit and folks w/ more experience involving units working on this order can chime in.

pen

 

[surviverguy]

The safety equipment for the boiler includes a standard pressure temperature (p/t) valve where the coil exits the stove and an expansion tank for potable water in the attick where the storage tanks are located. A small bronze circulator of about 20 watts is used to assist the thermosyphoning. A Stecca differential controller with sensors on the stove (boiler) water piping is used to control the circulator. Two insulated 40 gallon hot water heater tanks in the attick provide storage. This stored hot water serves as preheated water for another wired hot water heater in a bathroom closet on the main level of the house. A flat plate heat exchanger inside an unpressurized buffer tank in the basement for the radiant floor is also connected to the storage tanks in the attick.
I had to keep the stove door open to start fires before installing the oak also. The only diffences I notice comparing pre-oak operation to this years operation is 1) more blue flames in the upper section of the firebox and 2)greater heat output using less wood per day and 3) quicker to get up to operating temperature (above 250 degrees). Start up times that used to take about 30 minutes now occur in about 10 minutes.

 

[surviverguy]

My wood was not as dry as ideal as many of the posters have mentioned and the heat reclaimer reduces the draft. The heating season is over now. I will clean and inspect the chimney in the next few weeks. I think I'll eliminate the reclaimer to get better draft and less creosote and get my wood drying better organized. I think the intake piping is undersized and I'll make it larger and try burning next season without the draft fan. Thanks for the recommendations to all those that took the time to post comments. Would I be better off closing down the inake supply air or closing down the exhaust when the fires are nice and hot next season with the drier wood I am planning to use?

 

[surviverguy]

The other thing I noticed using the "oak" was higher humidity levels indoors (greater confort). Having tried both indoor drafting and sealed combustion using outdoor air, I'd have to say that burning with outdoor air is much better than using indoor air. The benefits are more heat with less wood and greater confort with more humidity.

 

[semipro]

I think the intake piping is undersized and I'll make it larger and try burning next season without the draft fan.

A thought on this... because gases expand when hot the OAK size does not need to be nearly as big as your flue pipe. I think most use OAK piping about 4" in diameter. If you use a 6" flue this is about right. Obviously more bends etc can cause restriction as you noted earlier.

If you want a technical basis for this, look up the "Ideal Gas Law". You can get a pretty good approximation of what size OAK is needed by PV/T (pressure times volume divided by temp) at the stove inlet equals PV/T at the outlet. For simplification you can assume the pressure of each is about he same and just compare V/T=V/T where temps are absolute (add 460 to F).

 

[surviverguy]

Semipro...thanks for that. I might try some calculations using the ideal gas law as you stated....but if 4" intake works good on stoves with 6" stacks, why try to reinvent that wheel? My current oak is way undersized. By comparison- 4" diameter intake piping (standard oak) has a cross sectional area of about 12.48 square inches. The oak I installed with its dual 1 1/2" piping has a whopping (or wimpy) 3.5 square inches. This oak also has several elbows used to get the piping from the floor to the stove's intake slots which are above its front door. I used dual piping to keep the "stove to pipe adapter" cool, whereas a single pipe tended to allow that adaptor to heat up hot enough to burn skin. A dual pipe equivalent of (4" oak) works out mathmaticaly to a diameter of about 2.82". I'll have to see what I can come up with....and If it were slight larger...like 3.00" it could always be restricted down (dampened) a bit....I planned to include some type of intake dampening to turn down hot fires when needed either for safety or for longer burn times.