Every engine on this site follows the same underlying discipline: a transparent, editable calculation built from your own inputs, using a named methodology, with clearly stated boundaries on what it does and does not claim to know. This resource lays out that discipline directly, using a handful of engines as examples of how it applies in practice.
Deterministic math, never a black box
The whole-home electrification payback engine runs the exact same simple-payback and comparison formulas documented in the methodology registry that every other engine uses. Nothing is estimated by an opaque model; every number traces back to a formula you can inspect on the methodology page.
Editable defaults, not hidden assumptions
The rooftop solar payback engine ships with reasonable planning defaults for every input, each labeled with its source, but nothing is locked. If you know your actual installed cost or rate differs from the default, changing it changes the answer immediately, with no separate "advanced mode" required.
Rate structures modeled honestly, not approximated away
The time-of-use versus flat rate engine models the actual billing structure it is comparing rather than collapsing everything into a single blended rate, since a real time-of-use or demand-charge bill does not behave like a flat-rate approximation.
Total-cost comparisons, not sticker-price comparisons
The battery versus generator total cost engine compares two options on upfront cost plus ongoing cost over your ownership horizon, the same total-cost discipline applied throughout the site rather than comparing only the initial purchase price.
Comparisons that respect what a fuel or equipment choice actually changes
The heat-pump versus standard electric water heater engine isolates the specific equipment-type comparison it claims to answer, rather than bundling in unrelated factors like financing or incentives that belong in a separate, more targeted engine.
What this method deliberately will not do
It will not size equipment, determine code compliance, verify incentive eligibility, or replace a contractor's quote or a professional energy audit. Every engine's claim boundary states this explicitly, because a purchase-economics tool that quietly overstepped into sizing or compliance territory would be making claims it cannot actually stand behind.
Frequently asked questions
Does RetrofitROI ever tell me what size equipment to buy?
No. Sizing, ampacity, and code-compliance math are deliberately out of scope; that work belongs to a licensed contractor or a dedicated trade-focused tool. RetrofitROI answers whether a purchase is worth it and which option wins on cost, not how to size it.
Where does a specific formula, like discounted payback, actually come from?
Every engine cites a specific methodology ID from the site's methodology registry, documented on the methodology page, so the same calculation logic is used consistently across every engine that relies on it.
Why does RetrofitROI ask me for so many inputs instead of just giving me an answer?
Because a one-number calculator that hides its assumptions is not more useful, it is just less honest about where the number came from. Editable inputs with visible defaults let you see exactly what is driving the answer and change anything you know is wrong for your situation.