Useing outside air for Gasifcation Boiler?

Not sure about America but here you cannot use inside air for any combustion appliance in a dwelling. Forbidden by code here & I would hope common sense everywhere else.

Perhaps some of the trades on the board can clarify code in America. I sure hope they say same applies south of 49 as well & that you have just seen some examples of DIY's gone wrong.

Doing things as you describe can have the unfortunate unintended consequence of killing the occupants. Usually in their sleep. Kids first, adults sometime later. Something to avoid.

It is certainly not common in the US to use outside air for combustion. Not yet.
The newer wood stove models and gas stove models all have it now available. I don't know if it is required by code.
The newer and more expensive gasification boilers all have it as an option.
What we notice is that for new construction or for high insulated homes almost always an "outside air kit" is ordered.
By code the outside air kit needs to be minimum 6" in diameter or similar.
With an outside air kit the overall efficiency of the installation is significantly higher. This makes sense of course, because you don't use the already warm inside air.

Garn has always used outdoor air for combustion. It just makes too much sense to not do so.

With an outside air kit the overall efficiency of the installation is significantly higher. This makes sense of course, because you don’t use the already warm inside air.

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While this seems to make intuitive sense, is it actually true? If cold outside air rather than warm inside air is combusted, are not additional btu's needed to warm the cold outside air, and therefore less btu's available for heating? Is not net efficiency the same, assuming the gasification boiler is designed to use cold outside air.

Of course, this does not mean that outside air should not be used for a variety of important reasons, but I wonder whether efficiency really is one of the reasons.

jebatty said:

With an outside air kit the overall efficiency of the installation is significantly higher. This makes sense of course, because you don’t use the already warm inside air.

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While this seems to make intuitive sense, is it actually true? If cold outside air rather than warm inside air is combusted, are not additional btu's needed to warm the cold outside air, and therefore less btu's available for heating? Is not net efficiency the same, assuming the gasification boiler is designed to use cold outside air.

Of course, this does not mean that outside air should not be used for a variety of important reasons, but I wonder whether efficiency really is one of the reasons.

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I was thinking the same thing.

I don't understand why all gassifiers aren't designed to be direct vented for oustside combustion air. I have a boiler room that I have to vent to the outside to provide combustion air to my Solo Innova. This will make the whole boiler room cold in the winter so I have to be concerned with freezing pipes and the like. If I could direct vent the boiler inside combustion room that wouldn't be a concern as the room could be heated. What gassifiers can be direct vented to the outside? I wasn't aware of any.

Mike

I have a boiler room that I have to vent to the outside to provide combustion air to my Solo Innova. This will make the whole boiler room cold in the winter so I have to be concerned with freezing pipes and the like.

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I have a Tarm Solo 40, I open a window about 6" when the boiler is firing, and then shut the window at the end of the burn. I can't even tell that the window is open by any movement of cold air (sometimes -40F outside). The air intake is the same as the flue exhaust, so no flood of cold air. Alternative could be a vent damper that is sync'd with the Tarm. Another alternative would be a duct with cold air trap. Not a big deal for me.

I am planning on trying a cold air trap. Glad to hear too much cold air in the room hasn't been an issue for you Jim. Hope I'll have the same good result.

Mike

Another alternative would be a duct with cold air trap

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Jim
Could you point me to a previous post describing the "cold air trap" or a explanation of same?

Thanks

Will

Cold combustion air can lead to a few issues on a gasifier... increased creosote in the upper chamber, increased moisture from condensation, poor secondary combustion, a gummed up heat exchanger, and premature refractory failure to name a few. This would be mostly true on units installed without thermal storage where the constant on off cycling of hot/cold air through the boiler takes its toll. To be sure, the effects of cold combustion air are probably more dire on a wood gasifier than the average person might think.

If cold outside combustion air is going to be used, it really needs be heated up to room temperature before it enters the boiler... and the easiest way to do this is to just pull air from inside the home, but this leads to a whole 'nother issue of having enough air flow into the home to satisfy the requirements for combustion. Most newer homes are too air tight to expect that adequate combustion air can be drawn in through the cracks, and in many cases negative pressure in the boiler room can cause products of combustion to be drawn backwards down the chimney, through the boiler and into the home... an annoying if not dangerous situation. A passive vent can sometimes cure this, but even those have issues - depending on which direction the wind is blowing, if a passive vent is on the low pressure side of the house, again, negative pressure can be created making the draft situation worse. There are a few products out there that have fans and dampers that can be wired to the controls on your boiler so that adequate air is always available for combustion. These are a great way to solve draft problems, the down side is that they might cost a grand to install. I am sure the code writing people would love to have a regulation to throw on the books that would force the use of these units, but the fact is, every set up is different, and they wouldn't actually be required in but a small percentage of installations.

As far as which way is more efficient... as jebatty said, either way you look at it, net efficiency is going to be the same (as long as the air can be preheated in some fashion). Most indoor wood gasifiers do not have large enough preheat chambers to warm up the cold winter air to room temperature... They're just not made for cold combustion air. Even our Froling with the preheat channels along the side of the vessel is not meant to be fed anything but room temperature air. A few of the outdoor units have larger preheat channels - it would be interesting to know how well they actually work.

cheers

Discussion HERE. The complication is calculating the required size/amount of makeup air. FWIW, take a look at Calculation.

If I remember correctly, the calculation resulted in about 250 sq in of vent opening for my boiler. There is some outside air leakage intp my shop, and with a little experimentation I found that if I opened the window about 6" (150 sq in +/-), there was no smoke spill out when I opened the door to add wood and the boiler performed very well. If the window was closed more than this, there would be smoke spill out, etc. So, I made the semi-educated guess that an OK opening was the size that would prevent smoke spill out. Of course, the draft fan would not be operating when the firebox door was opened, but natural draft with an open door was quite vigorous, maybe about the same draft as with the door closed and the fan "on."

The opened window is on the opposite side of my shop from the boiler, about 20' feet away, so there is plenty of time/air space for the cold outside air to warm and not cause a noticeable cold air draft in the shop from the open window, unless you stand right under the window. Sometimes I have forgotten to close the window after the boiler has burned out, bummer. If I forget to open the window when firing the boiler, the boiler lets me know because there is smoke spill out and the start is noticeably slow.

Opening a window for make-up air does not meet code requirements, to the best of my knowledge. The code looks for a "fail-safe" combustion make-up air supply.

Best of both worlds is outside air which is preheated before entering the combustion chamber. Pure cold air directly from outside will lower combustion temps in a lot of cases and that's something you don't want in a gasification system.

Efficiency lost by heating the combustion air is more than made up for by the improved burn characteristics achieved when you bring in air that's 100*+.

I use an outside air kit with preheat from the outgoing exhaust gases on my oil boiler. I never really checked the stack temp difference between 80 deg outside temps verses -20 deg temps. I am pretty sure I don't reach the dew point temp but will check it out next season. I certainly would not want sub zero supply air going into my boiler, especially during the post purge cycles.