My mind must be getting a little loose. I always thought heating was accomplished by offering the biggest difference in temperature between the room and the heating element. Faster flow rates and higher temps realise higher return temps. Why temper the boiler water with the return? Does't that mean that several pumps are going to run for extended periods of time? More tons of coal? Simple always worked better for me. Perhaps running a separate zone to the "dumper" and using the two candles to read by is a warmer means to an end.
Thats old tech thinking - sorry please don't take that as a slap - its the same as we all used to think the only place for a circulator was on the return. Modern pumps are now able to live on the supply and if you read "Pumping Away" by Dan at http://www.heatinghelp.com/shopcart/pro ... gory=8-191
you will have a better understanding why.
Cooler lower gpm flow at a more constant rate in load loops produces a more efficient, constant, comfortable room - vs - hi temp circulation and bang bang on off circulation that overheats a radiator and causes hi low temperature swings in the room just like forced scorched air heating does.
Why temper the water back to the boiler??? So the boiler isn't introduced to large swings in temperature caused by circulating cold zone water directly back to it. But if you circulate cooler water longer that possibility is also greatly reduced. Yes that means the circ pumps will run longer - but now we use low wattage modern cartridge pumps that do not cost an arm and a leg to run - plus you run the boiler less and you use less solid fuel, you also have less thermal expansion cycles on engine and energy transmission piping.
You like my dumper analogy? Gotta keep warm somehow sometimes!
Down load the free heat loss calculator from http://slantfin.com/heat-loss-software.html
- measure the radiation of each loop and the heat loss of each area and you can calculate just how low a temperature of water you can circulate to maintain design room comfort vs outdoor temperature. The less energy you need to produce in the boiler to heat you place the less fuel you need to buy and the huge side benefit - you will be more comfortable with cooler radiators because the rooms will be evenly, gracefully, quietly, heated.