I need to heat several bedrooms with direct vent natural gas heaters due to high electric bills (also California does not allow the use of the inexpensive vent-free models). However new direct vent heaters cost an arm and a leg-easily $400 and up. Does anyone know where I can buy used heaters-for instance a website for contractors who have pulled heaters out of walls when they remodel a home- and who want to resell the heaters. Or has anyone heard of converting a cheap vent-free gas heater to a direct-vent heater? The manufacturers I have contacted say they know of no such conversion but with ingenuity it may be possible.