I've a Masport free standing cast iron firebox combustion heater, and its now on it's 27th Winter! It runs 24/7 from sometime in May through to September and at either end of the cooler months is lit at night. So about 6 months use, or about 180 days each year. That's 4860 days!!! For memory it was about $1600 installed, so it's cost me about $60.00 a year or $0.33 a day. It's longevity comes from it having a cast iron firebox rather than mild steel, which burn out. Some of the cheapies with a 5 year warranty don't make it through their 6th year!!!