I don't have a low-water cutoff because I have a hot water boiler. I went and ordered a 19x20", 3 row water/air coil and I think it will be fine. The coil is rated at ~160k BTU, my existing furnace is 144k BTU or 114,500 NET output. The TACO 007 is rated at 20gpm, my blower fan is 3/4HP so all together I think I'll have a warm basement and the house will at least be as warm as last year and my pockets will be stuffed with the cash that I'd ordinarily give the Propane company. The only downside is I'll never use the full capacity of the EFM boiler with my current setup, 25 pounds of coal per hour will make more heat than I can ever hope to dissipate through a 20x22" plenum. It's also 2 tons of coal a week
if I need to burn that much to keep warm I'm buying a winter house in Jamaica mon. I didn't test my water but my HW heater is 15 years old and still good so I imagine it's OK. There is the option of running separate zones to baseboards or radiators but not this year.