Methodology
How we research
A guide is only as good as its sources. Here is exactly how we build and check ours.
Last updated:
1. Start from the reader’s question
Each guide starts with a question a homeowner actually asks, such as “Is a heat pump cheaper to run than my gas furnace?” or “Can I still get a tax credit for insulation?” We write the short answer first, then the detail.
2. Gather primary sources
We collect the official material behind the answer: laws and IRS guidance for tax questions; DOE program notices, NASEO’s launch tracker and state energy office pages for rebates; ENERGY STAR specifications and DOE guidance for equipment; EIA data for prices and energy use; HHS and DOE pages for bill assistance and weatherization.
3. Check every claim
A second team member checks each factual sentence against its source before publication. If a figure cannot be verified, it is removed or shown as a range with a caveat. Where sources conflict, for example an agency page that still shows an old tax credit, we use the most recent authoritative source and explain the discrepancy in the guide.
4. Date it
Every guide shows a published date, a last-updated date and a reviewed date. Every source shows the date we checked it. Incentive status shows the date of our last check.
5. Build calculators with visible maths
Our calculators run entirely in your browser. Each one:
- shows its formula and every constant with a source (for example, 1 therm = 100,000 BTU; 1 kWh = 3,412 BTU);
- uses dated default prices from EIA that you can replace with your own;
- validates inputs and explains errors in plain language;
- is covered by automated tests that check the formulas against hand-worked examples.
6. Review and update
We review incentive-related content regularly and immediately after major changes. Equipment and efficiency guides are reviewed at least once a year. Changes are reflected in the “last updated” date, and significant corrections are logged on our corrections page.
What we do not do
We do not accept payment for coverage, publish product rankings based on commissions, invent statistics or testimonials, or give individual tax, legal or financial advice. Read our editorial policy for the full rules.
Questions people ask
Which sources do you trust most?
Federal agencies and official program pages come first: the U.S. Department of Energy, ENERGY STAR, the IRS, the Energy Information Administration, HHS for LIHEAP, and state energy offices for state rebates. We also use national laboratory research and standards bodies such as NFRC for window ratings. Commercial pages are never our source of fact.
Why do your numbers sometimes differ from other websites?
Usually because we use the newest official figure and say what date it applies to, while other pages repeat old numbers. For example, many pages still advertise federal tax credits that ended for installations after December 31, 2025. When official sources disagree with each other, we say so and explain which one we used.
How accurate are your calculators?
The maths is exact for the formula shown, and we test every formula with automated unit tests. The result is only as good as the inputs and the simplifying assumptions, which we list on each calculator page. Treat results as planning estimates, not quotes.
How often do you check incentive status?
We re-check federal and state incentive status regularly and whenever a law, IRS notice, DOE program notice or state program launch changes things. The date of the last check is shown at the top of every page.
Do you test products?
No. We do not run product tests or publish product reviews. We explain ratings and test standards such as SEER2, HSPF2, UEF and U-factor so you can compare products using their certified ratings.
Can I see your sources?
Yes. Every guide and calculator page ends with a numbered list of sources, each with the date we checked it. Links go to the original pages so you can verify anything we say.