Garn air intake question

So your real question is what is the friction loss in 12 inches of 7 inch pipe. If you have an issue, Dude it isn't an extra foot of pipe. If it makes ya feel better, change it out to 8 inch. but it will be a waste of you Saturday.

Sorry I though 2 elbows and 4 ft of pipe + 8 ft of pipe was 13 ft of pipe Sorry I transposed the 7 & 8. Now it's two feet over, the 12 ft + two elbows. Got a duct calculator in front of me and I believe you can't even measure the difference of the two in velocity or static pressure. Cal Martin and ask him? Sure there is some fudge built in.

Kemer, If I were doing your install I would be using 8" pipe and ells and reducing at your fittings as needed.
I know you would be safe there.

A Garn needs 300+cfm at full burn and pulling, not pushing, that through 7" pipe is iffy with the 2 ells in it. Personally, I would rather have the intake coming from outside for the simple reason that you are not using conditioned room air and wasting the heat in it.

The result of the garn will be that it wil puff sooner and longer with more intake resistance. Of course it will depend on the volatility of your wood, dryer smaller loose packed splits will make it worse. As suggested if you need the ducting to get outside air, go larger to decrease the resistance.

Harry - what are your flue temps like? Are you getting a lot of puffing? Can you route the intake to the side rather than up and over?

Your temps sound OK. If the Garn is not puffing substantially or at all, then circumstantially it appears you have enough inlet air flow. Up-sizing the inlet piping will certainly go a long way to compensating for the extra restriction due to length and turns. There are ways to test the flow using a manometer, but it's probably not worth doing that.

Pulling air from the room is possible, providing you have adequate inflow to the room. Otherwise you will have the same problem (restricted inlet flow). Opening the door does not help because it disrupts the distribution of air flow to the nozzles. I have opened the door to stop heavy puffing, but only for a few seconds.

Hi Harry:

Yes, with my horizontal flue....all 7' of it out to the garbage can (no screen on the can yet at all), and about 5' of pipe on the air intake (straight into the garn, no elbows), I still see the occasional "spark". Not sure what you mean by an ember. They will come out and blow around in the "flue breeze". Yes, they leave the can (no screen). Would they leave the can with a 1" or 1/2" mesh on it? I'd think so. They don't last long....maybe a few seconds. Can they start a fire? Obviously not this time of year. After three weeks of heat in August without rain? That's a good question.....

So if you are trying to remove these totally and absolutely, I still see them....and I don't think I can have anything shorter or more air.

Now, if you are getting "coals" or anything with significant mass....then I think that's a different story. Do these things leave your roof area? You have asphalt shingles?

Sometimes bigger things will get pulled through, and I can hear them rattle through the squirrel cage blower....but I have not seen any big "coals" sitting in the barrel ever.

Harry,

I see the same a pbirger is seeing. You can click on my signature link and see my set-up pics.

Rick

A couple questions for you Kemer....

How dry is your wood? Reason I ask is that I have noticed on a number of Garns that if the wood is very dry or if some of it is getting a little dozy, it will tend to crumble as it burns. When these pieces breakdown and fall apart in the firebox during operation, sparks will sometimes make it all the way through the entire 50 feet of heat exchanger tube and exit the flue. Mixing a little "greener" fuel in with the load on top of the very dry stuff will retard the combustion process a bit and maybe prevent some of the sparks from entering the air stream.
Have you upsized the intake yet and have you noticed any effect?

I wouldn't recommend going completely vertical with your intake as it would be possible under some circumstances to create a reverse air flow back up the intake when the blower is off. This would allow relatively hot gas leftover in the combustion chamber to find their way out of the intake which of course is only single wall pipe and not made to handle any heat.

Harry - you are still welcome to come up and see my unit during a burn. I do see small incandescant particles make it to the discharge elbow and blow around briefly, but I have not seen any "fireworks" or anything large enough to be a hazard or concern.

BTW - I burn just about every kind of (dry) wood imaginable, including some pretty punky stuff. I also burn a lot of Eastern White Pine and Hemlock. In my experience the wood type has not made much difference in the number of glowing particles I see at the discharge point.

Harry - I would suggest you leave the first section of intake piping in place and upgrade the diameter from the first seam on out. Up-sizing those elbows will help with the flow especially.

Adding my $.02 here.
Hankovitch from SW Wisconsin communicating. I just got my GARN 2000 up-and-running the first week of January. We will be heating three 'floors' of a 36' x 104' Barn/Home with this unit.
I burn 100% kiln-dried pallet wood which I get from a local company where they have a large band saw they use to literally cut apart pallets, and then they rebuild pallets with the usable wood. The splintered, cracked, busted or odd-sized pieces they put in ~4'x4'x4' 'boxes' and either burn themselves to heat their 36,000 sq ft warehouse or sell to people like me who want to burn wood but are too lazy to cut, split, stack, and dry tree wood. The pallet wood comes with nails, but virtually all nails are IN the wood (nothing sticking out) since they cut the pallets apart and the band saw blade just cuts right through the nails.
My Burn Experience follows........For the first 10 days of burning I experienced an absolutely HORRIFIC problem with puffing/huffing for 15-30 minutes into my burn. With a reasonable or large wood load I found that unless I leaned on the door to keep it shut for the first 15-30 minutes of the burn I would have my Garn Room FULL of smoke. Alternatively if I put in a very small load of wood (enough for a 30-minute-burn-to-ash) could I burn without huffing. Boy was I frustrated. I was thinking I might have to cut trees, haul wood out of a forested area, split it, stack it, dry it.....etc......not what I wanted to do. I can drive 16 miles, get 3 'boxes' of wood (1.5 Cords) loaded into my horse trailer, haul it home, take the boxes out using our Bobcat....and in an hour I have 1.5 cords of wood in storage. The cost of the wood is approximately twice the cost of the gasoline to make the round-trip!
Can you tell that I am frugal and lazy?!
I scoured this and other Forums to find out what others had done to minimize......or maybe even eliminate(?!!) Puffing.
Bottom line from a half day reading various forums ------ The problem was TOTALLY SOLVED (emphasis intended) by simply building and maintaining my wood load in the rear 75-80% of the Garn's burn chamber. Boy, was I relieved!
I use about 24" long pieces of pallet wood (I cut all pallet pieces in half), carefully load/stack/ the wood into the chamber leaving about 4" to 6" of space from the end of the wood to the secondary burn chamber, and light it up. NOTE: when I say I carefully load the wood I mean I load it with as little air space between pieces as possible.
I do use the extra Burn Brick, not lying flat but on-edge, placed in about 3" from the door.
I always get a smooth, even, efficient burn with not even a hint that the unit may start puffing and huffing...nothin' but water vapor coming out of my horizontal flue.
I hope this helps others who have similar problems with burning wood which would be considered 'too dry' by much of the wood burning community, and I thank those who provided the solution (it was not my idea, I just used what others were kind enough to share, and am now passing it forward).

What Hankovitch is witness to is the fact that it's easy to get too much of the wood "involved" in the fire at one time in a Garn. This is due to the volume of air moving through the combustion chamber. As he said, leave as little air gap between you wood as possible especially if it is ultra dry or fine diameter. With smaller pieces a person can easily get too much surface area exposed and soon even the Garn's combustion motor can't supply enough to satisfy what the burn rate wants to be. Puff the magic Dragon appears and you get sparks and embers galore out of the exhaust + unnecessary smoking because the unit is actually going positive/negative pressure in the firebox trying to "breathe" and get enough air.
I'd say Hank's got the method pretty well nailed down.

Thank you. It's now been two weeks since my first burn with my all kiln-dried wood pile shoved close to (within 2-4" of) the ceramic liner of the secondary burn chamber. I've had only a single burn (out of a couple dozen) where I had about four belches (puffs?!), otherwise the burning of my pallet wood has been blissfully uneventful.... so all's well. Thanks to everyone who contributes to the Hearth Forum!