Outdoor Woodboilers Part II

To burn or not to burn?

The bottom line is this; having a high demand for BTU’s and stacking your cold firebox with small splits of dry wood, mixed in with medium size splits, creates a minimal amount of pollution. If those conditions are met- the wood boiler will spew out heavy white smoke at first and then trail down to no visible smoke within 1/2 hour. You can add dry wood later, when large amounts of red coals are still burning and only have visible smoke for about 5- 10 minutes, then the stack will go back to clear or minimal smoke conditions. I do not burn all day and night, only one cold start in the early morning and maybe adding wood one or two more times depending on the outside temperature or if we are doing laundry. By then the house is warmer than I want and I let the oil boiler take over for the rest of the day, setting the thermostat for 61 degrees at night. Currently we are heading into the end of the heating season and after a year long quest to minimize the woodboiler pollution problem, I think I have figured it out.

Stacking your wood like this will allow the critical burn temperature to be reached quickly and no smoke will be visible from the stack within 1/2 hour causing minimal pollution.

Upon initial start up this is the kind of smoke you will get. With dry wood and a properly stacked firebox- no smoke will be visible within 1/2 hour.
In less than 2 hours my firebox burns down to this condition. This is the perfect time to add more wood. For best results add some small stuff with the bigger splits. In my experience as long as there is demand for heat the new wood will only smoke mildly for 10 minutes or less and then revert back to a smokeless condition.

In the spring of 2018 I had a lot of time to think about my wood boiler pollution problem since I was home recovering from a second hip replacement. I found some free online courses at Heatspring Magazine about buffer tanks and how to configure them into a system to create efficiencies. https://blog.heatspring.com/2-pipe-versus-4-pipe-buffer-tank-configurations/.  I knew that a buffer tank would help greatly in smoothing out my issues with the wood boiler and wanted to learn more about them. John Siegenthaler was the instructor and at the end of the brief course he referenced this article: https://www.pmmag.com/articles/86583-a-signature-system-br-john-siegenthaler . It was written in 2003 and references a heating contractor in Alaska who incorporated a large inverse, indirect hot water heater to use as a buffer tank.

This article on water heaters rang some loud bells in my brain because the previous winter I ran into a problem with my on-demand propane water heater failing during 10°F and below outside temperatures. Icing in the propane tank valve would restrict the flow of the propane. The kitchen stove would work fine but the narrowing of the valve orifice from icing would cause the propane hot water heater to shut down because the propane demand could not be met. We would be without hot water till the temperature warmed up or the sun came around and hit the propane tank. The point being, I couldn’t rationalize a large 200-gallon buffer tank filled with expensive antifreeze but I could rationalize a 72-gallon inverse, indirect hot water tank if I gained additional benefits.

The TurboMax arrived at the end of August

            During the fall of 2018 I was determine not to let what happen to me the previous winter happen the next. I wanted to be ready for the cold weather as soon as it hit and use the wood boiler from the get go. In the beginning of September I started working on the new primary piping configuration to incorporate the TurboMax. The pressure was on because I had to shut down the heating system to do it. The wood stove would have to suffice in the mean time. 

The TurboMax operates inverse to a normal indirect hot water tank in that the boiler water circulates around copper domestic water coils.

The guy in Alaska was using what is called an inverse indirect hot water tank. The TurboMax http://www.thermo2000.com/content/en-US/s2_produits/optimizer.aspx is inverse in that it has copper coils for domestic hot water running through it, instead of the typical other way around; hot boiler water running through copper tubes in a domestic, indirect, hot water tank. The largest tank TurboMax sold held 119 gallons of boiler water; the largest tank that would fit in my basement was the 72-gallon version. This is the kind of hot water heater that would be normally used in a large home or apartment building with multiple units. For me it could work as a buffer tank for my boiler water and secondarily heat my hot water. This is what the contractor in Alaska used it for; buffering a very large system in a residential home.

My new hydronic heating system design incorporating the TurboMax

Incorporating the TurboMax required rerouting the primary piping circuit. The primary circuit was now going to include the TurboMax, it would run directly through it. I did not add another pump for the TurboMax because the primary circuit already had one. The TurboMax had 1 1/2” fittings so with the primary circuit being 1 1/4″; I did not think it would add enough extra flow resistance to require a dedicated pump. Part of re-configuring the primary circuit required piping closely spaced T’s for the Guest House secondary circuit and installing a pump. 

Getting the TurboMax into the basement required some creativity.
This is the expansion of my primary circuit to include the TurboMax. The pump and insulated duelpex are visible center. I included a bypass so if someday I needed to make changes, it could be done without shutting down the house heating system.

         I commissioned the new system including the TurboMax by mid October and was very pleased with the results. Previously, I was always concerned that sometimes the oil boiler would go on and off for short periods of time and it seemed to short cycle, (even though the people at Biasi said reaching 125° was good enough). After installing the TurboMax in the primary loop the short burst stopped and became longer, more sustained. Apparently because of the large volume of hot water stored in the TurboMax, the low temperature, radiant floor heating system was satisfied for longer periods of time. The boiler would fire for longer because of the larger volume of water in the system. That was what this new plan was all about. The TurboMax would buffer either boiler. When the freezing weather eventually hit I was able to confirm that the 72 gallons in the TurbMax did indeed buffer the Wood Boiler. Usually the TurboMax would be sitting at anywhere from 90° to 115°, hot enough to satisfy the house demand. When I fired up the wood boiler, those additional gallons allowed the damper to stay open long enough for the OWB firebox to reach the critical burn temperature for the smoke to stop and not pollute so much before it started to close. When the wood boiler was burning the TurboMax would stay at 125 to 155ºF, depending on the outside temperature or whether laundry was being done or showers were in use.

    I installed a Caleffi mixing valve on top of the TurboMax for domestic hot water and routed the return through the Rheem, tankless, propane on-demand hot water heater. I did not connect the TurboMax aquastat to the system because that was not my priority. Although I wasn’t sure about that, it turned out to be a beautiful thing. Cold water would first circulate through the Turbomax, then 16′ later, enter the tankless hot water heater. So if the hot water hadn’t been running, the tankless would always fire initially to heat the 16′ of cool water in the 3/4″ pipe and continue to fire or not depending on the temperature of the TurboMax and the set point of the tankless water heater. We set ours at 112°F. I started to use a lot less propane because the temperature going into the tankless was much hotter than the 40-50° temperature coming out of the deep well. In extremely cold weather, I never ran out of hot water because the OWB was usually burning, keeping the TurbowMax anywhere from 120°F to 155°F, causing the on-demand hot water heater not to fire. One morning at -8°F it did shut down temporarily but the water became hot once the TurboMax flow reached the spigot. Problem solved!

       The insulated, 1″ duel Pex, heat pipe for the guesthouse had been run in previous years but the distribution and radiators were not. I wanted all this to be done by Thanksgiving for my house full of guest but because of supply issues the Biasi radiators had to be back ordered form Italy. So the TurboMax system worked but no hydronic heat went to the guesthouse. The good thing was I was able to use the wood boiler for Thanksgiving. It was sorely needed because we had the coldest Thanksgiving weekend up in the mountains I have ever experienced getting down to 9°F one morning.

In December the radiators came in and I was able to install them in the guest house. I hooked up the overheat aquastat to the woodboiler and set it at 185°F to turn on the guesthouse pump for the dump zone radiators. It works like a charm so I don’t have to worry about the damper closing down and causing a smoky condition. Getting to this point was not easy but overall I am feeling pretty good about burning hardwood from my land to help heat my home. Solar panels will be coming eventually to reduce my carbon footprint.

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