The old system was base on a coal fired back boiler which was not operating very efficiently. We replaced the old boiler with a Si20 back boiler from Stove Innovation. unfortunately the stove doesn’t have an MCS certificate, so we could not use the Boiler Upgrade Scheme.
The heat source is the Si20 back boiler, the heating system is open vented.
Two circuits are connected to the stove, one of them is gravity circulated, the other is pumped.
The gravity circuit has only one radiator on it. In case of a power cut this radiator is taking away the heat from the stove saving it from boiling.
All other radiators in the house are connected to the pumped circuit, which is controlled by a room thermostat and a motorised valve.
The top coil of the twin coil cylinder is also connected to the pump circuit.
Schematics 1.7
To put the new stove where the old one was located previously, a new lintel had to be installed.
Location of stove
To avoid draft in the room around stove we installed an air pipe under the floorboards coming from outside going directly behind the stove with a cast iron grille on the hearth.
Twin coil hot water cylinder
After using the system for a couple of days it turned out that the gravity radiator is overheating that room. At the same time the production of hot water was very slow.
Reducing the water flow in the gravity radiator would have been a solution to these problems, but then the safety function of the gravity circuit would have been compromised.
This is why we have installed another motorised valve which is closed when there is electric power and the water flow of the gravitiy circuit is reduced. But in case of power cut this motorised valve opens and the gravity radiator can work with full capacity.
At the same time we had connected the bottom coil of the hot water cylinder to the gravity circuit to make it possible to produce hot water even if there is no electric power.
