This is a Thermo Control Model 2500 without insulation enclosure (unclad) being installed in a basement. The flue pipe was run through the ash cleanout bin under the existing fireplace and through the fireplace floor utilizing the flue/chimney of the fireplace.

The challenge on this install was gaining access through the ash dump area under the existing fireplace and then expanding the ash drop hole to accomodate the 8 inch. black pipe. The black pipe extended through the fireplace and attached to a custom adapter plate at the flue.

The adapter plate is usually custom made, first by making a templet and then having a welder fabricate one out of steel. The adapter plate must be sealed and screwed inside the top of the fireplace so there will be no air going up the chimney except whatever is coming up the black stovepipe from the wood burning boiler below.

The fireplace face/front is finished off with decorative metal to hide the black pipe and also keep anyone from touching it. There is usally nice heat coming off this pipe and it gives a nice effect in the room it is in.

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This stove is connected to the oil burning boiler using 1 1/2" black pipe.  (pictures #1&2) The circulator is drawing water from the return line at the bottom of the oil boiler and pushing it into the bottom of the water chamber on the wood burning boiler, forcing the hottest water at the top of the water chamber in the wood burning boiler back into the feed manifold of the oil boiler. (picture #3)

This is a primary loop that is constantly keeping the oil boiler supplied with ready to use hot water. The aquastat on the oil boiler is set much lower than the wood burning boiler just as a backup but really should never come on. In most instances, the burner can be switched off but the thermostats, zone valves and circulators are left on to operate as normal.

When a zone in the house calls for heat, the zone valve opens and the circulator dedicated to that zone comes on forcing the returning water from the zone through the return line. Instead of being pushed into the oil boiler, it takes the path of least resistance which is straight to the circulator pushing the water into the wood burning boiler.

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The devise mounted on the DVL pipe with the wire coming from the metal box on the wall is called a stack limit switch. (picture #5) This sensor detects when the pipe hits a specified temperature and cuts power to the air flap on the fill door regardless of what the aquastat is calling for. The stack limit switch and the aquastat work in conjunction with each other and create a dwell.

These two simple switchs stoke and starve the boiler for air. When the air door on the front of the stove closes, it starves the primary burn chamber for air and draws more air through the secondary air tubes into the secondary burn chamber. The chimney temperature will actually rise after the stack limit switch cuts the air to the primary burn chamber. As soon as the stack drops within limit, the cycle starts and another round of stoke and starve happens.

When the secondary chamber is sucking the hot air in and combining it with the air starved gases of the primary burn chamber, this is the most efficient time of gasification causing the stove to be 76% efficient. This gasification process is happening even while stoking but it is most evident just after a stoking session.

Some other points of interest with this wood burning boiler installation is the fact that the flue pipe off the top of the stove was an indoor double wall pipe called a DVL (Double-wall interior stovepipe for connecting wood stoves to chimney)

Due to the fact that the clearances were very tight passing by the staircase above. As you can see, the customer installed a 1/2 inch thick concrete board on 1 inch standoffs to isolate the double wall pipe from the combustable staircase.

This double wall pipe allows for minimal clearances down to 6 inchs. from combustables. The 90 deg. turn in any chimney pipe is not desirable but for obvious reasons it was required here. The flue is tall and the draft is stronge so this was an acceptable configuration.


Call us to discuss your installation configuration. We'll gladly spend as much time as you need. 845-797-2205 8am to 8pm est.