kinnscience wrote:Just installed an efm 700 and have the 7 gallon DC running into the water heater. Calculations from our end showed that it was better to run electric during the summer, but only slight difference with coal. Previously had the DC on the oil boiler running into the HWH, with bypasses to use only the HWH during summer months. During Fall and Spring it was a toss up and will probably run the boiler from October through the first half of April .. maybe all of April. Your mileage may vary, especially with smaller Coal burner units.
One piece of advice given to me via Rob Roy, make sure if you run the DC into the HWH that you have a bypass if you are shutting down the coal burner in the summer. It is not a good idea to run cold water through your DC.
I agree with Rob's advice, and would add that for a similar reason you should lean toward running the unit all summer rather than letting it sit. It's not easy to get all of the ash out of a 700, and ash + summer humidity is not a good formula for the boiler.
If you are going to run a 700 for DHW, I'm not sure why you'd want to use the HWH at all, especially in the summer. With an appropriate tempering valve (thanks, Sting
), you should get abundant DHW from the large reserve of btu's in the boiler water and the formidable power of the stoker. And when doing any calculations regarding summer use, you might want to consider the benefits of the coal boiler as a dehumidifier. When we used a 900 to make DHW in the summer, the draw of air for the stoker, the chimney draft and fugitive heat from the boiler let us retire our conventional dehumidifier and the portion of the electric bill it created.