Boiler questions

[waynecub]

Looking for advice about a Harman SF-260 boiler.
I will only be burning wood.
I am thinking about buying a used Harman SF-260. The boiler looks to be in very good condition, used two or three years.
Do these boiler have a good reputation?
Can this boiler be used with out storage tank? No room for storage tank in basement.
Are the boilers hard to keep clean of creosote?
Should I put in a damper in the stack? My chimney is 8" X 8" and has very good draft.
The boiler is for sale for $1,500.
I have a old Franks boiler that needs to be replaced, this has been a good boiler in the past.

 

[NateB]

I don't know about these boilers, but I can address questions 5 and 6
Can you use it without storage? I am sure you can, but it would be good to match your heat load to your boiler output, or you will get a lot of creosote.
Are they hard to keep clean? No if you can run them till they are out of fuel, but if you idle the boiler due to no demand. You will get creosote and a big mess to clean up often.

 

[TCaldwell]

I had a sf260 for 13 years, all above is true however it really is just a inside smoke dragon. They aren’t designed for a clean burn with wood, coal works better for the sf260, 1500$ is a lot of money for this boiler used, possibly 500 max. FYI, I burned 13 full cord a year with this boiler suplimenting with oil, installed a garn at same house, 7 cord! I’d save my money for a used gasifier with storage.

 

[waynecub]

I had a sf260 for 13 years, all above is true however it really is just a inside smoke dragon. They aren’t designed for a clean burn with wood, coal works better for the sf260, 1500$ is a lot of money for this boiler used, possibly 500 max. FYI, I burned 13 full cord a year with this boiler suplimenting with oil, installed a garn at same house, 7 cord! I’d save my money for a used gasifier with storage.

Thank you NateB and TCaldwell
I'm going to keep looking for something that will be a gasifire.

 

[peakbagger]

IMHO You still need storage to make it worth installing a boiler.

 

[waynecub]

I do have room to put in a 80 gal. hot water tank. ( old glass lined elec. hot water tank ) Not sure how much this will help?

 

[maple1]

That wouldn't be worth the effort. I have 660 and would like 1000.

But it mainly depends on how good your boiler is and how much extra heat it makes beyond what the house is using.

 

[peakbagger]

I have seen the results of three boilers without storage. One was on a large house with high heat load. It burned full open to keep up with the house demand so the oil burner didn't have to run 24/7. On the other install it was closer to a typical install and it was bad with creosote and air quality issues, both related to how the boiler responds to a lack of demand by shutting the air supply. Once the air flap closes it goes to incomplete combustion that skunks out the neighborhood and fills the stack with creosote. The third install is my neighbors former install. he had multiple chimney fires which ruined a tile liner. He then switched to insulated liner and managed to have enough chimney fires that he melted the liner. He had a ladder permanently tied to his chimney and was cleaning monthly. I got my boiler for free and until I added storage I only dared use it during very cold conditions or warming the house up after I was gone for a few days. Once I added storage, my wood usage went down and I stopped buying oil and haven't done so for 5 years.

If you need modulating load go with pellet stove or pellet boiler. If you don't need heat they don't feed pellets so far less issues with part load operation.

 

[Drewby]

I have seen the results of three boilers without storage. One was on a large house with high heat load. It burned full open to keep up with the house demand so the oil burner didn't have to run 24/7. On the other install it was closer to a typical install and it was bad with creosote and air quality issues, both related to how the boiler responds to a lack of demand by shutting the air supply. Once the air flap closes it goes to incomplete combustion that skunks out the neighborhood and fills the stack with creosote. The third install is my neighbors former install. he had multiple chimney fires which ruined a tile liner. He then switched to insulated liner and managed to have enough chimney fires that he melted the liner. He had a ladder permanently tied to his chimney and was cleaning monthly. I got my boiler for free and until I added storage I only dared use it during very cold conditions or warming the house up after I was gone for a few days. Once I added storage, my wood usage went down and I stopped buying oil and haven't done so for 5 years.

If you need modulating load go with pellet stove or pellet boiler. If you don't need heat they don't feed pellets so far less issues with part load operation.

What kind of boiler is yours? Mine is an old school non gasser and I’m trying to decide if storage will cut my wood usage down and help clean up the burn. My load is very high heating a large bldg. This is my first winter and I plowed through about 15 full cords of wood, 2500 lbs of hard coal and 400 gallons of propane. I am considering heat storage if it reduces the wood usage. With that being said the boiler doesn’t idle too much in the really cold times and has pretty high stack temps which seems to keep the chimney clean at the expense of fuel.

 

[peakbagger]

My boiler is an old school non gasser. Its a wood/coal design with a bottom grate. Its close to 30 years old.

 

[maple1]

What kind of boiler is yours? Mine is an old school non gasser and I’m trying to decide if storage will cut my wood usage down and help clean up the burn. My load is very high heating a large bldg. This is my first winter and I plowed through about 15 full cords of wood, 2500 lbs of hard coal and 400 gallons of propane. I am considering heat storage if it reduces the wood usage. With that being said the boiler doesn’t idle too much in the really cold times and has pretty high stack temps which seems to keep the chimney clean at the expense of fuel.

You likely won't improve your situation much without a better boiler.

 

[Drewby]

My boiler is an old school non gasser. Its a wood/coal design with a bottom grate. Its close to 30 years old.

My unit is similar. It doesn’t have much for over fire air though. Just two small 1” holes straight in front of the blower fan. Does your unit have any over fire air for secondary burn?

 

[peakbagger]

I do not have secondary air. I get all the air I need in through the bottom grate to support the way I burn it which is flat out for two or three hours a night to fill the storage during the coldest part of the year. I expect I could gain some efficiency if I had a way of introducing heated secondary air but the configuration of the boiler means putting it in would require major alterations to a 30 year old boiler. I expect the efficiency gained for putting storage in far exceeded if I introduced heated secondary air. When this boiler eventually is unusable I will definitely go with a more modern unit, but I got this one for free and cut my wood and oil usage down to the point where I have not bought oil for 5 years and expect I live in an area that has similar if not even a colder heating season than LaCrosse WI.

I am fan of the KISS approach and this Burnham design is pretty simple, no blowers. Many of the newer designs are more complex, use more refractory and require far more maintenance over the long term. My chimney is a conventional interior tile lined masonry that is about 32' tall.I built the house in 1988 and inspect the chimney yearly. It has never really needed cleaning but I have cleaned it three times in 30 years mostly out of guilt. 20 years of it were with properly sized wood stoves run for optimum burn rather than for extended burn times.

 

[maple1]

My unit is similar. It doesn’t have much for over fire air though. Just two small 1” holes straight in front of the blower fan. Does your unit have any over fire air for secondary burn?

Practically speaking, you won't get any secondary burn in a boiler unless it is a gasifier. Or very little and not without going through hoops without knowing what the results will be. You are dealing with a liquid cooled firebox, after all.

Old school boilers are even more hampered by their lack of heat exchanging ability. Any heat that gets made in the firebox has a straight exit to the chimney. There are or were some that had heat exchanging tubes. Not sure if yours does or not. But they can also be problematic in that they get dirty fairly quickly and need frequent cleaning to maintain what efficiency they contributed. Which is a messy job with those things.

In post 8 above, my old one was in the first category. Not that we have a huge heat load, but the boiler had low output to the house due to all its inefficiencies. I was a slave to it for 17 years, for 6 months a year. Damned near killed me. I could have lessened that some by letting the oil burner do more work but that noise was like nails on a chalkboard every time it cut in (expensive ones).

 

[peakbagger]

One of my talents is tuning up biomass power boilers. They are set up with bottom grates with preheated primary air and secondary air ports. located at various spots along the combustion path. A big part of the tune up is to deliberately change the flow of air through the grates and secondary air ports fed with preheated air methodically and plotting the impact on emissions. It takes 20 minutes or so for the boiler to stabilize after a change and I take a minimum of 20 minutes of data so it takes awhile. I have to track CO and NOx as CO is sign of low temperature and NOx is sign of high temperature. The goal is to hit the sweet spot where the CO is fully burnt while the NOx is minimized. The usual method used to reduce overall emissions is to stretch out the fireball in the boiler so it doesnt burn too hot and introduce staged secondary combustion air at points in the fireball to ensure there is enough O2 to combust the CO. The problem is once the flame temp drops to a certain temp I can pump all the air I want to into the flame and the CO will not ignite. If I really crank up the primary grate air I can get some low CO but the NOx goes up quickly and if fuel distribution is not just right I can melt the grate bars due to a process called torching which is caused by poor fuel distribution. Its a "rubiks cube" with lots of variables. Most operations are pretty good on running efficiently but some operators are not so good.

Small boilers are not regulated for NOx so pouring on the primary air and getting a small compact fireball can lead to pretty clean burning. As long as there is adequate heat transfer area they can be pretty efficient. I have considered putting an economizer section on my boiler to extend the heat exchanger area but have not done it. A gasifier is effectively breaking the combustion into two areas, the primary firebox is intentionally fed with usually heated primary air but not enough air to fully combust the wood. Its give off volatile gases to the secondary chamber which is usually insulated with refractory. The fuel is now a gas instead of solid so turbulent combustion is a lot easier and the refractory keeps things hot enough for the CO to be burnt off. The downstream heat exchanger gas paths can be smaller and more complex and can be controlled to a lower temperature to get more heat out of the boiler as the boiler does not need to worry about unburnt condensable vapors condensing out on the tubes and forming creosote. This process also allows a higher turn down although most gasifier companies require storage so turn down is not an issue. Try and turn down a conventional boiler by throttling the air and the result is unburnt gases and condensable vapors end up plating out the in the heat exchanger tubes or the stack and causing all sort of bad things to happen. The trade off is I can burn crappier wetter wood if I was stupid enough to do so albeit I will get more creosote. Try that with gasifier and it will have to be run on bypass or it will crap up.

 

[Drewby]

I just want to modify my boiler to introduce some heated secondary air in the right places and maybe install a heat baffle to create a hotter area within the firebox to assist in some secondary burning.
The advantages of my boiler are the fact that it can burn anything including coal pretty well.
If a person can burn coal well I don’t believe they will ever fell the same about wood again. With that said I still want to burn both. My wood is free to an extent and then after that if I pay for anything it will be coal for sure.
I just cannot in any way pencil out a new gasifier system as a cost savings in any way. And I will burn 20 full cords of wood on a cold year. So if a gasser saved me 10 cords that’s about $1500 of processed wood a year, it would take 10 years at least. And I doubt they will save me that much wood over my well tuned old style boiler.

 

[peakbagger]

My Burnham has heat baffles over the firebox. They are made of steel and only last so long before they droop and burn out. They slide in and out so I have to bend them back straight occasionally and replace them when they burn out. I think it came with a different alloy plate originally but I just get a new batch made up every few years.

 

[waynecub]

I have enjoyed all of this conversation that has been posted. Thank you all. I was thinking of taking a used Harman SF-260 boiler and adding heated secondary air above the fire. I was thinking of using two aquastats, one for primary air and one for secondary air. When running the primary air will shut off at 170 and the second air will shut off at 180. Question, will this make for a slower shut down and less creosote build up?
I'm a steel fabricator so this would be fun to try and make run cleaner.
Thanks Peakbagger, it helps to understand whats going on in that hot box.

 

[TCaldwell]

Because the water jacket surrounds the firebox, it keeps the environment too cool for secondary air to make a contribution. You would need to create a insulated refractory chamber to introduce the secondary air to the fluegas for a reburn. Then you would need increased water to flue gas heat exchange capability.

 

[Drewby]

How about making a baffle of some sort within to contain the burn and the fresh air just under it in an effort to make a small fireball inside the burn chamber? I am going to try something like that in mine. It will be similar to the wood stove that other have modified to get secondary burning above the fire. I realize it will not be a complete burn but maybe a partial gassification to clean up the smoke and create a hotter firebox with less primary air to extend the fuel supply so it doesn’t get burned so fast.
In essence it will keep the heat reflected back at the top of the wood for a very hot spot right above it with fresh oxygen.

 

[waynecub]

Maybe I should build a new boiler one that has the water storage and heat transfer tubes over the top of the fire box. The transfer tubes would run horizontal ( 2" tubes 8 tube ) and the water storage would be over the top of the tubes. Clean out door for cleaning the tubes. No water on the sides or back or front just insolation and refractory. Add air under the grates and heated secondary air over the top. Run the primary air and secondary air separately. Build a bypass damper in the back to help with smoke out the front door when loading.
Opening the loading door to reload might cause the unit to woof?
You all are helping me a great deal. Thank you.
Marcus

 

[TCaldwell]

I think it’s a good decision not to buy and modify the sf260, the results wouldn’t be worth it. If you feel comfortable fabricating a boiler, I’d try to follow a proven design rather than wing it.

 

[peakbagger]

I have a refractory lined pit and baffles, The water jacket completely surround the boiler but the pit is inside the jacket I could rig up secondary air but without access to cast iron parts they wouldnt last long.