The specs an owner actually needs.
Independent, numbers-first answers about the equipment in your home: what the spec actually means, what size you need, and which part fits.
Short answer
21,000 grainsA four-person household on 10 gpg water, regenerating every 7 days, needs 21,000 grains of softener capacity between regenerations. Nearest nominal size: 24,000 grains.
Browse by what you own
290 pages, four ways in: diagnose a symptom, size a unit, match a part, compare a shortlist.
Water 151 pages
Home water treatment: diagnose a symptom or lab result, size a softener or filter, match a model number to its part, and compare the units worth a shortlist.
Most asked
Plumbing 82 pages
Home plumbing: diagnose a leak, a freeze risk or a noise, size a heat cable or a pressure tank, match a model number to its part, and compare the gear worth a shortlist.
Most asked
Air 57 pages
Home air equipment: purifiers, humidifiers, furnace filters, CO and smoke alarms, space heaters, smart thermostats, air quality monitors and radon. Size it to the room, match the filter, compare the units worth a shortlist.
Most asked
Before Prime Day and Black Friday
What to check before a discount decides for you. Live prices sit on Amazon's own cards, never in our copy.
Plumbing deal check
Shower head and faucet Black Friday deal check
Air deal check
Smart thermostat Black Friday deal check: wire first
Air deal check
Space heater Black Friday deal check: safety first
Air deal check
Air purifier Black Friday deal check: CADR first
Plumbing deal check
Bidet Black Friday and Prime Day deal check
Plumbing deal check
Dehumidifier Black Friday deal check: 65 F rating
Air deal check
Humidifier Black Friday deal check: output and water
Water deal check
Reverse osmosis Black Friday and Prime Day deal check
Water deal check
Water filter Black Friday and Prime Day deal check
Water deal check
Water softener Black Friday deal check: sizing
Latest pages
Air · Diagnose
Aux heat vs emergency heat on a heat pump
AUX HEAT is automatic backup running with the heat pump; EM HEAT is a manual switch that locks the compressor out. Google says aux costs about 2 to 5 times as much.
Air · Diagnose
Heat pump blowing cold air: defrost or fault?
Carrier prints 85–100°F as normal heat pump supply air and a 5–10 minute defrost; Lennox 5–15 minutes every 30–90. Ice over 1/4 inch after defrost is a fault.
Plumbing · Diagnose
Water heater blanket: worth it? DOE's 7% to 16%
DOE's 2017 guide: a tank warm to the touch can save 7% to 16% with a blanket, pipe wrap 3% to 4% more. A. O. Smith and an electric manual say newer tanks need none.
Plumbing · Compare
New homeowner gifts: leak sensors, alarms, test kits
Eight housewarming gifts, each for a month-one check: USFA alarms on every level, EPA radon test below the third floor, the 80 psi code limit, CDC well test.
Air · Size
Space heater size calculator: watts per sq ft, BTU
Watts = length x width x 10 W per sq ft at an 8 ft ceiling (Dimplex, Stelpro), 12.5 at 10 ft. A 10 x 14 ft room needs 1,400 W: one 1,500 W heater.
Plumbing · Size
Water heater recovery time calculator
Recovery GPH = input x efficiency / (8.33 x temperature rise). A 4,500 W element at a 90 F rise gives 20.5 GPH, so a 40-gallon tank reheats in about 117 minutes.
Why the numbers here check out
Most equipment questions have one correct answer and it is a number. How many grains of capacity for four people on 22 gpg water. What micron rating a sediment filter needs on a well. Which cartridge fits a housing you already own.
Those answers are usually published by whoever wants to sell you the hardware. OwnerSpec publishes them independently: the formula, the inputs, the working, and the source it came from, so you can check it rather than trust it.
Independent
No manufacturer, dealer or installer owns a number on this site. Affiliate links are disclosed on every page that carries one.
Cited to the source
Limits come from EPA, NSF/ANSI, UL and extension services by number. Capacities and part numbers come from the manufacturer's own manual or data sheet.
Dated
Every page shows when its facts were last verified and last updated, so you know how old the number is before you use it.