Guides
Each guide explains one decision and has the calculator for it built in.
- Heat pump vs gas furnace: which costs less to heatWhether a heat pump or a gas furnace is cheaper to run comes down to one comparison: the price of electricity against the price of gas. Enter your numbers below, then read how the comparison works.
- How much does it cost to run a mini splitThe cost comes from the power the unit draws and how long it runs. Enter the size and rating of your mini split below to see the cost per hour, per day and per month.
- What size air conditioner do I needFor a window or wall air conditioner, the size comes from the area of the room and a few adjustments. Enter the room below, then read how each step works and where the method stops.
- How much electricity does a central AC useThere is no single number: it depends on the size of the system, its rating and the hours it runs. Enter yours below, then see how each one changes the bill.
- Window AC vs central AC costA window unit is cheap to buy and cools one room. A central system costs more and cools the whole house. Enter both below to see the running cost and the payback.
- Tankless vs tank water heater costThe label efficiency is only part of it. What you pay in a year depends on how much hot water you use and what gas and electricity cost where you live. Compare two heaters below.
- How much does a space heater cost to runThe cost is the watts, times the hours it runs, times your price per kWh. Enter your heater below, then read how to lower it.
- Electric car vs gas car cost per mileCost per mile is the easiest way to compare them. Enter your car and your gasoline price below, then see how much the price of electricity in each state changes the answer.
How the guides work
Each guide takes one decision a homeowner faces, such as whether to heat with a heat pump or a gas furnace, what size air conditioner a room needs, or what a tank water heater costs to run next to a tankless one. It explains the factors that matter in plain language, shows a worked example, and puts the calculator for that decision on the same page so you can try your own numbers.
The figures in a guide come from public sources, such as the U.S. Energy Information Administration and ENERGY STAR, and each guide lists its sources and the date it was last reviewed. Tables compare states or options using those figures, and where a number is an assumption made for an example, the guide says so. Guides give estimates for planning, not quotes or engineering advice. See themethodology and sources page for how data is chosen and checked, and the disclaimerfor the limits of the results.