Tools

Calculators and lookups

Quick answers with the working shown. Every tool names its formula, its sources and the day its prices were last checked.

5Tools

EIAPrice source

October 2026Last checked

Heating and cooling

What does it cost to run a space heater, fan or AC?

Cost per hour, night, month and season for any plug-in heater, fan or window AC, at your state's electricity rate. Compare two appliances side by side.

Open the tool →Heating

How long will a propane tank last on my heater?

Hours a propane cylinder or tank lasts on any heater, with the cost per hour, per day and per month at your state's propane price, next to a plug-in electric heater.

Open the tool →Heating and cooling

What size heater or AC does my room need?

The BTU size of window AC, portable AC or mini split, or the watts and BTUs of a space heater, for your room's square feet, ceiling height, sun and climate.

Open the tool →Cooling

What size ceiling fan do I need, and how long a downrod?

The blade span your room needs and the downrod length for your ceiling, with a to-scale drawing of the fan in the room.

Open the tool →Heating

What is the cheapest way to heat a home in my state?

Ranks gas, electric, heat pump, propane, oil and kerosene heat by cost per million Btu delivered, at your state's EIA prices.

Open the tool →

About these tools

Each calculator is built from public figures: electricity, propane, heating oil and natural gas prices from the U.S. Energy Information Administration, sizing tables from ENERGY STAR and the makers, and the specifications printed on the products we review. The page shows the formula in plain words, a worked example and the assumptions you can change.

Prices are refreshed by hand, and each tool prints the date of the figures it uses. If you spot a number that looks off, tell us.

28 tricks to cut your energy bills

One free cheat-sheet by email. That's it.

Get the free cheat-sheet →