Thermal numeracy refers to understanding the quantities of heat produced, emitted, and transferred in various physical phenomena.
- BTU - 1 lb water raise by 1 degree F
- BTU of wood is 8k-9k per lb -
- U value of insulation is BTU/(hr*sq ft*deg F). It is the inverse of R value - 
- Fireplace heat loss from chimney can be 80-90% - 
- At high temperatures, temperature in degrees F is about 2x that of degrees C. Specifically, ~9/5 times.
- Glenwood 5000 stove is rated for 100k BTU, with 11 sf of heat exchange area - about 10k BTU/SF
- 1 kW ~ 3000 BTU/hr
- Black pipe is only $12/square foot (10k BTU) of heat exchange area using 1" pipe! - 
- 1/2" PEX power production - 22 BTU/hr for 1 foot of length - . 500 feet per trough = 11k BTU
- Cord of wood is $235, and 4000 lb - 
- Thermal expansion coefficient of water is 1/10000 for F -