Methodology and Calculator Assumptions

We separate three kinds of information: physical relationships, planning heuristics, and facts that require current verification. The distinction matters because a temperature-rise calculation can be reproducible while a local installation price remains uncertain.

System and brand comparisons

System comparisons use hot-water demand, site suitability, available energy supply, installation scope, operating behavior, and service access. A recommendation should change when those conditions change. We do not assign an invented numerical score to every technology or manufacturer.

Brand profiles describe published ranges and the questions to ask about a specific model, warranty, and local service. They do not establish lifetime reliability from anecdotes or claim hands-on testing. Use the brand shortlist together with the installer checklist.

Cost planning

The cost calculator combines centrally maintained equipment and installation allowances with explicit project inputs. These are editorial planning bands, not statistical market-price estimates. They exclude automatic rebate deductions because eligibility and funding are not established by equipment type alone.

The most useful comparison is an itemized installed proposal for the same scope. Emergency timing, access, local labor, supply upgrades, and code corrections can move a real price outside a planning range. The calculator explains its additions and keeps major exclusions visible.

Storage demand and first-hour rating

The size calculator uses household context and busiest-hour fixture assumptions to produce a starting range. It cannot measure your heater’s recovery, plumbing temperature, mixing arrangement, or actual bathing behavior.

Tank gallons describe storage volume. First-hour rating describes tested delivery over an hour with recovery. A planning range must still be compared with the exact model’s rating and operating mode; see first-hour rating.

Tankless flow and temperature rise

The tankless calculator sums concurrent fixture flows and subtracts incoming water temperature from target output temperature. The required heating load increases with both flow and temperature rise. Selection must use the manufacturer’s performance at that rise rather than a headline maximum GPM.

Fixture flows and simultaneous use are inputs, not measured facts about every home. Inlet temperatures vary by season and location. Gas input and electrical demand cannot be inferred from output heat alone without accounting for efficiency and equipment design.

Incentive records

The rebate finder stores sources, dates, technology, jurisdiction, and eligibility notes. A matched record is a lead for verification, not approval. Records with uncertain dates or incomplete eligibility remain qualified as such. Programs can change or exhaust funding after verification.

Read the editorial policy for how evidence and corrections are handled. Exact equipment manuals, current program rules, and local professional assessment complete the decision.