gallon of natural gas has ~84,000 BTUs in it.
gallon of propane has ~91,500 BTUs in it.
... in case anyone was wanting to calculate the relative cost assuming heat's desired since some of us are heading into Winter.
Using my own #s for example:
Our house uses ~50MBTU/year for heat.
Electricity cost = $.145/KWh
1Wh=~3.4121BTUs
Propane cost (we buy in Summer, and holy Hell have prices risen) = $2.492/gal
Natural gas unavailable
For propane, I'd need ~546.45 gallons. Assuming 20% of heat is lost by heating rooms we have no reason to heat (closed ducts as well as ductwork and heater in basement [no purpose in heating basement with all its windows] all still leak significant amount of heat), this becomes 655.74 gallons. @$2.492/gal, that's $1,634.10/year to heat house.
For electric, I'd need 14,653.73KWh. Since I can strategically place miners, there is no wasted heat. My cost is $2124.79/year.
If we bought propane in Winter, of course, cost of electric vs. propane would be much, much closer (and electric would've been cheaper this last Winter). However, with these numbers, I simply need to earn ~$487.69 by mining in all of the cold season, where everything after is effectively profit. Assuming the 14,653.73KWh usage needs to be spread out over 140 days, this means I need to consume ~104.67KWh/day, or ~4.36KWh/day, which means I need ~4,361W in mining equipment.
Numbers can be improved by shutting miners off while we're asleep except in bedrooms while temperature difference in cold season can be countered by over-clocking/over-volting or under-clocking/under-volting. However, I'd rather keep things under-volted and deal with it being a little bit colder inside on most days -- of course, propane can still be used on extremely cold days.
Jump to: