About
Built to answer one question, correctly.
WhatSize Appliance exists to answer the question that millions of homeowners ask every year: "What size [appliance] do I need?"
Last reviewed: June 2026 • Read our full editorial policy
Standards-based
Every recommendation comes from public AHAM, DOE, ACCA Manual J, and NEC 702 publications — never vibes.
Transparent math
Click “How we calculated this” on any result to see the formula, the multipliers, and the cited standard, step by step.
Always free
No paywalls, no signups. We earn a small Amazon commission when you buy through our links.
Who we are
WhatSize Appliance is run by a small editorial team of writers and researchers who specialize in appliance sizing standards. We are not a content-mill site, a generalist publisher, or an AI content farm. Every formula on this site is hand-coded against a published standard, every guide is reviewed by the editorial team, and every product pick is re-curated monthly.
Our research methodology is based on direct analysis of public industry standards — AHAM, DOE, ACCA, and NEC — combined with manufacturer spec sheets and published performance curves. You can read the full research process on the Editorial Policy page.
Our standards
Every calculator is built on publicly available standards — with the cited edition and section noted inside the “How we calculated this” panel on every result:
- AHAM AC-1 — Air cleaner CADR (Clean Air Delivery Rate) performance standard. Drives our air purifier calculator.
- AHAM DH-1 (DH-1-2022) — Dehumidifier performance standard. Drives our dehumidifier calculator.
- DOE 10 CFR Part 430 — Appliance energy and capacity standards, including First Hour Rating (FHR) for water heaters.
- ACCA Manual J (8th Edition) — Residential HVAC load calculation methodology. Our mini split calculator uses simplified factors inspired by Manual J principles, not a full Manual J calculation.
- NEC Article 702 (NFPA 70) — National Electrical Code, Optional Standby Systems. Our generator calculator applies the NEC continuous-load rule (125% of running watts) plus the largest starting surge, a standard engineering practice for generator sizing.
- Manufacturer spec sheets and published performance curves from Generac, Honda, Champion, Zoeller, Wayne, MrCool, DELLA, Frigidaire, Levoit, Bosch, Rheem, and others — for verified appliance wattage, BTU, and pumping performance where no public standard exists.
Editorial standards
Every calculator formula is reviewed against its source standard before publication. Every guide is reviewed for accuracy by the editorial team. Every product list is re-curated monthly. Cited standards are re-checked at least quarterly, and a “Last reviewed” date appears on every page.
For the full process — including our corrections policy, conflict-of-interest disclosure, and update cadence — see the Editorial Policy page.
Why we recommend products
WhatSize Appliance participates in the Amazon Services LLC Associates Program, an affiliate advertising program. When you buy a product through our links, we earn a small commission — at no extra cost to you. This is how we keep the calculators free.
Our product recommendations are based on verified specifications, independent review data, in-stock availability, and value. We do not favor higher-priced products because of a higher commission rate, and we disclose every conflict of interest on the Editorial Policy page.
Contact
For correction reports, partnership inquiries, or general questions, email [email protected] or use the Contact page. For suspected calculation or factual errors, please write to [email protected] — those reports are prioritized and acknowledged within two business days.