I bought my outdoor wood boiler in 2008 and have had a series of issues I wanted to address to make the boiler more user-friendly and efficient. Below you will find a series of images and descriptions documenting this process.
The boiler originally shipped with a rather rudimentary temperature control system consisting of a surface mount thermostat that cycled an electric blower on and off, and a manually adjusted draft door on the blower. I had a very difficult time regulating the temperature. I had frequent boil-overs and wide swings in water temp. I addressed the problem by adding a dry well, a solenoid, and a two stage digital aquastat that is set as follows:
180* - blower off and damper closed
<180* but >=175* - blower off and damper open
<175* - blower on and damper open
The idea is to only use the blower when needed, as it forces hot air out the chimney and wastes heat.
The second issue I faced, was what I personally define as “poor insulation”. The boiler used some type of fiberglass batting on the to and sides, and nothing on the bottom of the water jacket. I decided to strip the tin, and ultimately the framing from the boiler and prep for spray foam. I was a bit disappointed to find the outer shell of the water jacket also had no paint and was beginning to rust:
I also discovered the water jacket was not welded solid around the top of the boiler, which essentially left me with a 50 gal air space above the water level:
I sandblasted the boiler, welded the gaps, and sealed the welds with polyurethane roofing sealer for good measure, then painted the boiler and tacked on studs to attach tin:
I also cut and threaded the overflow pipe on the side to direct it up through the roof and reclaim that unused 50 gallons of airspace for water storage.
Before I welded that ridiculous inspection cover in place, I added a couple 90* and a few pieces of pipe to the inside of the return pipe to direct the water to the front of the boiler and promote better circulation. Unfortunately I forgot to take pictures of this step.
Once this long and laborious process was complete, I was ready to have the boiler insulated with closed cell spray foam. I kept the foam away from the door and chimney area, I used rock wool high-temp insulation for those areas, along with in-between the inner and outer firebox door panel:
The single wall chimney was also a source of problems for me. At least twice during the winter it would clog up and I would have to climb onto the shed roof and attempt to clean it out. I decided to cut the existing chimney off about 12” above the tank, and bought some nice triple wall insulated pipe and a cap. I reused most of the existing tin, but had to buy a few corner pieces and covered the furnace
I added a switch to cut the power to the damper and blower while loading the stove:
Since I spray foamed the bottom of the boiler and the hot coals sit in the ash pan and could potentially melt the foam, I thought it best to line the ash pan with half-height firebricks. These bricks also raise the floor of the firebox even with the bottom of the cleanout door, which is a nice benefit.
I think I may also experiment with lining the floor and possibly the firebox walls with firebrick in an attempt to raise combustion temps and further improve efficiency. I’m going to experiment with a secondary burn air tube plumbed from the ash pan area, up along chimney, and along the ceiling of the firebox. I’ve drilled a series of holes in the pipe that runs along the firebox ceiling in hope that the air will help ignite the wood gasses and initiate a secondary burn. I’m not fully sold this will work, but it was an easy modification while I was working on the boiler:
From the factory, the door gaskets consist of a large bead of hi-temp silicone, which on my boiler, melted away every year. I decided to clean off the sealing area and glue a 1”x1/4” strip of nomex to both doors. If I can’t seal the firebox, all the sophisticated controls in the world won’t properly regulate the temperature.
I know I’ve missed a few items, and need more and better pictures of others, but this should be a good start. I’ll keep track of wood usage this winter to document any improvements. In the past winters, I’ve used about 12-14 full cord of hardwood to heat a three level (including finished basement) 3000ft house to 72*, an 800ft garage to 55*, and an 800ft apartment above the garage to 72*. Everything but the apartment has radiant floor heat, and both are well insulated. On the coldest spells, 3 days or more of constant below 20 weather, I had to load the boiler up to four times per day, and it would still never reach a 175* set point, the blower ran constantly.
In case you didn't notice in the pictures, there are actually two different 290's we did the same modifications on, so there is a mix of pictures.
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Topic: How I improved my shaver boiler model 290 (Read 32564 times)