About
One question, answered from the source
Foundry Northwest, Foundry NW for short, makes free tools that answer the question you ask right before an expensive purchase for your home: what size do I need?
What it is
Ten tools so far, one question each: mini splits, generators, pool gallons with pumps and heaters, tankless and tank water heaters, attic insulation, dehumidifiers, window air conditioners, water softeners and portable power stations.
Each tool follows a method someone else published. Most come from ENERGY STAR or the U.S. Department of Energy. Others come from a building or energy code, a state code, a university extension service or, for generators, the maker's own published method. The tool quotes the source, links it, and shows the date it was checked.
Why it exists
Bigger isn't better. ENERGY STAR warns that an oversized air conditioner costs more, wastes energy and can leave a room damp and clammy. energy.gov says an oversized water heater costs more to buy and to run. The right size is a number you can look up, if you know where.
So each tool does the looking up, does the math in front of you, and stops where the published method stops. When the honest answer is "have a pro run the numbers", the tool says that.
How the numbers are handled
- Every number comes from a published source, quoted on the page.
- Nothing is estimated. If a number isn't published, the tool asks you for it or says it can't answer that part.
- Every step of the math is shown, line by line.
- Products are real, current models in the size you need, with specs from the maker's own page or spec sheet. A blank means the maker doesn't publish that number.
- Where a source disagrees with itself, the tool says which version it follows. TankSizer, for one, notes that energy.gov's worked example adds up to 65 gallons, not the 66 it prints.
The full list of methods and sources is on How we size.
What it isn't
A tool's answer is a starting point, not a load calculation, an electrical design or an installation plan. For whole-home systems, gas, electrical panels and 240-volt circuits, or structural work, have a licensed pro confirm the numbers. The terms and disclaimer say more.
How it's paid for
The tools are free, with no sign-up and no ads. Some show "check price" buttons, which are affiliate links to HVACDirect and Amazon. If you buy through one, Foundry NW may earn a commission at no extra cost to you. The size comes first, from the published method, and a button never changes it. The affiliate disclosure has the details.
Where it is
Foundry Northwest is based in Washington State. The tools are written for homes in the United States, and the climate zones, codes and agencies they use are American.