Tarm Flue Temperature?

[jebatty]

I have self-installed a Tarm Solo Plus 40 wood gassification boiler and am looking for advice on achieving the proper flue gas temperature. The instructions indicate that flue gas (with a Condor probe thermometer) should be 600F or more. This suggests that 600F is probably optimum for maximum efficiency, as higher temperatures would mean wasted heat up the chimney. I am burning pine (white, red and jack) slab wood, simply because that is the wood I have. It is dried to 10-15% as shown by a moisture meter. Burns typically are reaching flue temperatures of 800-900F and then gradually settle down as the wood is consumed. I have restricted the draft fan damper to the maximum permitted by its adjustment. I also have installed a motor speed control on the draft fan and slowed it down in order to prevent burn temperatures from going higher. I have long burn times, as I am using about 800 gallons of water storage with a plate heat exchanger off the boiler. I do not have turbulators on the boiler heat exchanger tubes. Your ideas and experience will be appreciated.

 

[Eric Johnson]

Welcome to the Boiler Room, jebatty. Always good to have another Tarm user here.

I think the stack temps should be lower. I think 250 to 300 is about optimum, but that's with turbulators. I seem to recall that they're higher if you don't have them installed. I'd try turning the secondary air valves down a bit and see if it has an effect on the stack temp.

I'm curious about your heat storage. Are you using the flat plate for heat exchange into the tank. If so, can you explain how you set it up. A few other people around here are considering doing that. I was at one time, as well. Also, what kind of tank?

 

[Reggie Dunlap]

I also have a Tarm. My stack temps run about 600 in gasification burning hard maple, beech, and yellow birch mostly. I installed turbulators and I can't see any difference in stack temp. The turbulators were $180 from Tarm, i wouldn't buy them until you have checked out all the other options. Eric mentioned the secondary air, I just leave mine in the middle and it seems fine. You could call Tarm's 1 800 number for their advice. They have a couple technical gurus there and I call whenever I have a question. They are pretty helpful.

Also, the Tarm manual says 600 degree stack temps are normal.

 

[brad068]

Welcome to the Boiler Room, jebatty. Always good to have another Tarm user here.

I think the stack temps should be lower. I think 250 to 300 is about optimum, but that's with turbulators. I seem to recall that they're higher if you don't have them installed. I'd try turning the secondary air valves down a bit and see if it has an effect on the stack temp.

I'm curious about your heat storage. Are you using the flat plate for heat exchange into the tank. If so, can you explain how you set it up. A few other people around here are considering doing that. I was at one time, as well. Also, what kind of tank?

Eric,

I often wondered why you guys with storage tanks didn't opt for heat plates instead of building large submerged hx. I thought that it was because you would need another circ and they do suggest that they be removed and descaled once in a while depending on systems. I purchased a 30 plater for my dhw and still need one for my in floor. I seen owb installers around here install these hx bypassing and turning off the water heater because these hx can transfer heat so well they can satisfy any demand, like a on demand water heater.

 

[Reggie Dunlap]

Garn- You are right a guy could easily make his own turbulators. They don't have to be pretty they just need to disrupt the air flow. After receiving mine from Tarm I thought I could have come up with something similar for a lot less money.

 

[kuribo]

600f exhaust temps seem very high....you are definitely losing heat and efficiency at that level. Based on what I have read and heard, with gasification and heat extraction, 300-350f is about where these 70-80+ ïficiency figures are seen....

 

[Eric Johnson]

Welcome to the Boiler Room, jebatty. Always good to have another Tarm user here.

I think the stack temps should be lower. I think 250 to 300 is about optimum, but that's with turbulators. I seem to recall that they're higher if you don't have them installed. I'd try turning the secondary air valves down a bit and see if it has an effect on the stack temp.

I'm curious about your heat storage. Are you using the flat plate for heat exchange into the tank. If so, can you explain how you set it up. A few other people around here are considering doing that. I was at one time, as well. Also, what kind of tank?

Eric,

I often wondered why you guys with storage tanks didn't opt for heat plates instead of building large submerged hx. I thought that it was because you would need another circ and they do suggest that they be removed and descaled once in a while depending on systems. I purchased a 30 plater for my dhw and still need one for my in floor. I seen owb installers around here install these hx bypassing and turning off the water heater because these hx can transfer heat so well they can satisfy any demand, like a on demand water heater.

I originally planned to use a flat plate hx, which I happen to have on hand, to heat the tank. But then I got enamored of stratification and the whole in-tank hx idea, so I figured I'd use the flat plate to heat my greenhouse. Which is one of the many things I still have to do. Right now it's piped directly to the EKO.

Another concern with the flat plate is that you'd have to run dip tubes into the tank, and I couldn't figure out how to position them. I guess in the middle of the tank would be best. You could run the supply into the bottom of the tank and take the return off the top, but that only works well for heat recovery. Heat storage would suck with that piping arrangement. Ditto if you piped it the other way. You could rig up a reverse-flow arrangement, I guess.

The final concern on the flat plate is the integrity of the pump on the nonpressurized side. I'd worry about cavitation and the possibity of it running dry. You'd have to mount it below the water line and then hope it stays primed. Or you could run a pipe out the bottom of the tank, but that means putting holes in the rubber liner. And you should probably have a bronze circulator, though I'd probably just use cast iron and replace it as needed.

All of these obstacles can be overcome, for sure, but not by me this time. If my fancy copper hx fails as predicted, I'll probably try couple of cast iron radiators submerged in the tank. It seems to me that would be a pretty good way to go.

 

[bbb123]

When I installed my Tarm I remember them telling me not to put turbulators in until you consistantly have flue temps. above 400. I try to clean mine every couple weeks, this and the turbulators I keep stack around 400. 800-900 degrees is way to high in my opinion you need some turbulators. Like Reggie said it wouldn't take much to make a set but I think they would cut your wood use down alot.

 

[jebatty]

Welcome to the Boiler Room, jebatty. Always good to have another Tarm user here.

I think the stack temps should be lower. I think 250 to 300 is about optimum, but that's with turbulators. I seem to recall that they're higher if you don't have them installed. I'd try turning the secondary air valves down a bit and see if it has an effect on the stack temp.

I'm curious about your heat storage. Are you using the flat plate for heat exchange into the tank. If so, can you explain how you set it up. A few other people around here are considering doing that. I was at one time, as well. Also, what kind of tank?

I'm puzzled by your comment and comments of others as to desirable stack temp of 250-400 or so when Tarm says stack temp should be 600 or more ("or more" not further qualified). Why this discrepancy??? I did call Tarm and they indicated that the pine could be too dry and I might mix in other wood; also to install turbulators which should reduce stack temp by at least 100; and/or also install a barometric damper. I did install the barometric damper, and it helps, but it also draws warmed air from my heated shop up the stack and certainly reduces efficiency. I am trying for solutions which will not use the the barometric damper. Further help/explanation will be appreciated.

I will add another reply on the HX setup under a separate heading "Plate Heat Exchanger Setup"

 

[kuribo]

The lower the stack temp, the more heat from combustion is being transfered from the flue gases into the water. Sending 400-500-600F flue gases out means that heat is being wasted....

Many gasification boiler makers tout their low flue gas temperatures along with no visible effluent as signs that the combustion is complete and efficient...

 

[Reggie Dunlap]

Kuribo- I don't think you can lump all brands of boilers together and say they should all run the same stack temp. They are not all designed to operate the same, what works in an EKO may not work in a Tarm and vice versa.

Tarm does say in the manual that 600 degrees is the target temp. Mine runs right about 600 with turbulators. I get good gasification, complete combustion, and no visible smoke.

Reggie

 

[kuribo]

I am not saying they all should output 300F flue gases, only that anything above that is wasting heat. If the Tarm is designed to output 600F flue gas, then the Tarm is not as efficient as others with lower outlet temps....

 

[sten]

I've been running a mostly self-installed Tarm 40 for a couple of weeks and was concerned that I couldn't attain anything above 400 F flue temps. w/o turbulators, burning 15% locust and oak. I recently put in the Tarm turbulators and don't get above 300 F and have noticeably faster heating of my 750 gallon tank as a result. It's reassuring to hear the opinion that these lower temps. are all right - it certainly seems reasonable that all conditions being met (dry wood, split small, etc.), that the lower temps. represent better efficiency.

Also wanted to add that I constructed a plywood and 2x4 tank, screwed and glued on the inner faces, screwed on the outer, through -bolted at the interfaces, with R-13 glass between studs (9 and 12" o.c.), and 2" ridgid foam outside, with and epdm liner, and think it's a decent way to build a tank that can be assembled in place and is well insulated. I used flat plate exchangers, one for the boiler to tank loop, one for the tank to load loop, and have the boiler intake at the bottom and return at the top, opposite for the load loop. The key to keeping them primed is the foot-valve, as used for pumps that draw from cisterns, etc. I'm not sure that the initial cost savings is substantial enough when considering the long-term cost to operate the additional pumps.

I had a question pertaining to safe tank temperatures - I've been running the storage tank to 150 F, but would prefer to run it higher if it were safe - I've done some research, but can't seem to find what the working limits of the epdm and blueboard foam might be. Any knowledge out there?

 

[Eric Johnson]

Hey, welcome to the Boiler Room, sten.

Each brand is different. My numbers are for the EKO line.

I think of it this way: If you have 2,000 degree temps in the gasification chamber and 300 degrees at the chimney, that's 1,700 degrees that was transferred into the water. Any excess stack temp represents lost potential heat. I think you're OK until you get down to around 120, at which point condensation becomes an issue.

On the EPDM, I think it's rated at 180, but you can push it to 190 with no problem. But the blueboard might be somewhat less. I used the more expensive yellow stuff with the foil layers. It's rated to around 200, I believe.

 

[leaddog]

I saw specs some where of over 200f on epdm. Think of a roof with black roofing in very bright sun.
leaddog

 

[EricV]

I have the Tarm Solo 40 and did install the turbolaters. Before I did I was right at the 600 mark that Tarm Specifies. When I purchased them the guys at Tarm said to not use them for the first month, not sure why but I followed his instructions. They also told me that the stack will drop with them installed. I run 450 now with them in.

I can't remember the guys name at Tarm I talked to but he was very helpful. give a call, they'll be happy to help. I've trusted those guys, after all Tarm has been around for 80 plus years.

As far as the EPDM it makes a difference what brand. I saw some in my shopping around that only were good for 140. I purchased the Firestone 60 mil because they rated it at 180.

I finally got my tank heating issue figured out but I'll post that under another thread.

In the past 3 weeks I've only burned about 3 gallons of oil, makes me all warm and fuzzy inside. I told my wife to can the monthly budget payment to the oil company. The last week of November and first week of December I was out of town so I had to burn oil, that was painful. Not that I can't afford it but knowing my Tarm was sitting there cold burned me up.

Eric

 

[bbb123]

I just got out my Tarm "directions" They tell you about them then they say "NOTE: TARM USA recommends that the turbulators NOT be installed when a boiler is first installed. Operate the boiler without the turbulators installed for a month or two until you can easily get the fire started and operating the flue temperatures of 600 F or more. Also note that constant flue temperatures of less than 300 F are too low when the turbulators ar installed.


Then they go on below to say why you cant achieve 600 deg.

1. bypass damper latched tightly
2. are vanes on fan clean
3. are your primary air channels open? (I have no idea where that even is???)
4. is your wood dry? Less than 15% MC 6" or less they want wood cut 2 years covered at least one year. (Most of my wood is 1 - 1 1/2 years)

I also have a plumbing diagram if anyone is interested.
One more note I cleaned out my flue pipe this year (about 5 foot horizontal) it had about 1/2 inch of ash on bottom of it.
I also checked the chimney and it was spotless (2 years of burning Tarm Solo, 5 years of burning Pacific Energy wood stove, and about 20 years of burning HS Tarm. Its never been cleaned.)