Thank you BallewBlade and kdogmcg. Glad to share my methods because its fun to have people to talk with who have a common interest and I have learned so much from this wonderful site I feel its just payback.
Im glad you like my forge/heat treating furnace. What makes that thing extra sweet is I built it on company time and got all the material for free, LOL. I would not worry about the heat factor because by forcing in air with a fan I get plenty of heat. As I stated I did some s90v and was able to get it up to 2150°F. And that was not the maximum I could attain either but I cant really go much higher than that not that I have a reason to but the limiting factors are my refractory material rating and my pyrometer only goes to 2200°F apparently.
Last year was a very cold winter around here so my bill was a little high but to be honest I really didnt notice a big difference from other years when I didnt use my heat treating oven so I would say its pretty cheap to run. And I did make a lot of Mokume-gane besides heat treating so I used it quite a bit. I do my tempering in a toaster oven though so I dont have to use gas for that. I do check the heat with my pyrometer though in my toaster oven so I know exactly how hot it is.
Heres a photo of when I did my s90v heat treatment and you can tell it is pretty warm. That glowing red plate on the front is quarter inch 304 stainless. I like the furnace too because my understanding is that natural gas has a carburizing flame so when I put bare metal in without foil I make sure I have a very rich flame so that there is almost no oxygen. I dont know if that helps but I have had great luck I feel heat treating in it with or without foil. Except for the micro-chipping on my s90v but I really think that is because I tempered at too low a temperature. I will know for sure after I try and re-temper at a higher temp.
And from what I read online natural gas in almost 1/3 the cost of propane for the same btu's. This is a few years old but so maybe it isn't that relevant now.
Here's a calculator that can assist homeowners in figuring out which method of heating a home is more economical:
www.eia.gov/neic/experts/heatcalc.xls
Based on that spreadsheet, here is the rough order, from low cost to higher cost, per million of BTUs:
- Geothermal heat pump $10.14
- Coal $10.47
- Natural Gas $13.24
- Elec Air Source Heat Pump $14.83
- Wood $16.53
- Corn $17.84 (see link for details)
- Wood Pellets $22.28
- Fuel Oil $31.15
- Kerosene $34.54
- Propane $37.48
See the spreadsheet for all the details and notes.