There are lots of electric boilers that would fit the Btu/h requirements you indicated and a Google search should find them quickly. If you didn’t already have a HR system, I would highly recommend that you consider a NextGen-8 appliance. The 8 stands for 8 kW. This appliance has a SS boiler, circulating pump, expansion tank, air vent, pressure relief valve, pressure differential valve, outdoor reset, modulation, control system and other worthwhile features you can’t get with any other pieced together installation (e.g., circulation pump exerciser that keeps pump from seizing up during non-heating season because of lack of use). Using a NextGen appliance results in a much less expensive and elegantly simple HR installation. However, a couple of questions first come to my mind...
12 GPM seems like an extremely large flow rate. As an example, we just did a HR floor heating system design for a 2400 sf home with slab emitter and outdoor design temperature of 26F and the flow rate requirement is only 1.8 GPM. So you must have a very large building, a very cold design temperature, an inefficient HR emitter, some combination of these, or 12 GPM is an invalid design parameter. I suspect this flow rate may be invalid and you are over-pumping. How did you come about using this high a flow rate?
Most air to air or air to water heat pumps have a built in aux heat system that kicks in at cold temps. Of course, the efficiency of the heat pump goes from a 3ish COP to a 1ish COP when this aux heat system operates, but you should still get the heat you need. So I wonder if your system does not have this or if it is not operating properly?
And finally, in order to select a circulating pump, in addition to the system flow rate, you also need the system head at this flow rate. |