Warm Air Heaters

How efficient is the E+ unit heater ? Can the E+ heater be used in both residential & commercial settings? Our site had a power cut and now our Rheco heater is in lockout, what do I do? Our site had a power cut and now our Photon heater is in lockout, what do I do? Can the heat exchanger be replaced on a ULSA heater? Can the heat exchanger be replaced on a PHOTON heater? Can the heat exchanger be replaced on a UDSA heater? Are the Rheco warm air heaters condensing heaters? Are the Photon warm air heaters condensing heaters?