Thanks Dave & Ray - I guess I view this as going from Kerosene, to something that has to burn more cleanly, and will be much easier to manage. If I thought the ProCom would not be efficient or functional, then I would definitely go with the Empire, but the size is quite a factor. The Empire heaters are big and heavy, and will require professional installation, as well as some serious greenhouse wall deconstruction. I would also loose an entire bench in the little greenhouse, due to the 3 foot verticle clearance required. With the ProCom, they are small enough that I can put the 20,000 BTU one in the isle, and will ask the plumber to make a disconnect, so I can remove it in the summer!
I have calibrated the BTUs, and am oversizing a bit.. 30,000 for the 10x20 attached, and 20,000 for the free standing. This is with an estimate temp of 58. I have in the past frequently let both greenhouses get into the 40s, so I think that these values will be sufficient in all but the most bitter weather, and then there is always the kerosene as backup!
I wish Empire made a smaller electric free heater, but they don't, so I guess I'll give the ProCom a try and see what happens. They HAVE to be better than Kerosene, which I've used for the past 6 years...
stef