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The calculator's own fields, action and results arrive with the verified pack when you load it. Nothing is computed in this page.
Home efficiency · the envelope summed
Whole-house envelope UA roll-up
Add a building up: component conductances — walls, roof, floor, glazing, doors, air leakage — summed into the whole-house UA figure other calculators use.
Verified engine
What the engine returns
The engine returns the whole-house conductance. Read the entries against the total before doing anything else: the largest line is the envelope’s dominant leak and the natural first candidate for the delta and payback pages that follow.
Inputs the result is built from
Number of components
Component 1 UA
Component 2 UA
Component 3 UA
Component 4 UA
Component 5 UA
Component 6 UA
Component 7 UA
Component 8 UA
How the result is derived
MethodEach participating component contributes its own conductance — area over resistance, with infiltration folded in as an equivalent — and the declared count masks entries beyond it before the parallel paths are summed into the whole-house total.
StandardEnvelope heat-transmission accounting: whole-building conductance as the sum of component UA values
GuardA component count of zero is refused — the pack ships the refusal as a declared test vector — because a ledger with no lines has no total, and returning nothing-summed as an answer would dress an empty census up as a tight house.
How a whole house becomes one conductance figure
A component UA states how many watts an assembly passes for each degree the indoors is held above the outdoors — its area spread over its thermal resistance. Heat paths through a wall, a roof and a window run side by side rather than in series, and parallel paths add as conductances: the whole-house figure is the column total of the entries, never a reciprocal of anything. That is why this page is a roll-up and not a formula — the physics has already been done inside each entry.
The census is where the honesty lives. Each entry must be counted once and only once: glazing and doors are their own lines, so the wall line carries the NET opaque area after those openings are subtracted, and a heated basement’s walls belong to the envelope while an interior partition never does. Double-counting inflates the total silently, and a forgotten ceiling understates it just as quietly — the roll-up is only as trustworthy as the inventory behind it.
The component count is a declared cursor, not decoration. Only the first however-many entries participate; anything typed beyond the count is deliberately ignored, and the pack ships a test vector proving a stale extra entry cannot leak into the total. That makes shortening a census an act of setting the count, not of zeroing boxes — and it means the count is the first thing to check when a total looks wrong.
Air leakage earns a line even though it is not a surface. Infiltration carries heat out as warm air rather than through a material, but over a season it behaves like one more conductance and is conventionally folded in as an equivalent UA — from a blower-door test or an air-change estimate. Leaving it off the ledger is the classic way an otherwise careful census understates a leaky house.
The total is the number the rest of this pack runs on. Multiplied by the climate’s accumulated degree-hours it becomes a season of heat loss; it is the conductance the thermostat-setback page pays restraint against; and it is the baseline the insulation pages perturb — the sibling delta page computes how much one entry shrinks, and this page says what it shrinks FROM. The largest line in the ledger is also the retrofit shortlist, unpriced.
Each participating component contributes its own conductance — area over resistance, with infiltration folded in as an equivalent — and the declared count masks entries beyond it before the parallel paths are summed into the whole-house total.
When this calculation is used
- Rolling an energy audit’s component table into the single whole-house conductance the degree-day and setback arithmetic consume.
- Rebuilding the total before and after a proposed measure — swap one entry for its upgraded value from the delta page and re-run.
- Triaging a retrofit: entering the census and reading which line dominates the sum, before any money is discussed.
- Sanity-checking an audit figure by reconstructing it from the parts, entry by entry.
Worked example
Run the pack’s declared reference census: a short ledger of a few live components — walls, roof and glazing, say — with the count set to exactly the lines entered and everything beyond it left to the default.
The engine returns the whole-house conductance. Read the entries against the total before doing anything else: the largest line is the envelope’s dominant leak and the natural first candidate for the delta and payback pages that follow.
Every figure in this example is produced by the certified engine when the calculator loads, checked against the signed pack’s declared test vectors; nothing on this page stores an answer. One declared vector plants a stale entry beyond the count and shows the total ignoring it — the cursor doing its job.
What each input represents
Number of components
How many of the entries below participate in the total, from one to eight. Entries beyond the count are ignored by construction — the pack proves it with a declared vector — so trimming a census means lowering the count, not clearing boxes.
Component 1 UA
The first line of the census and the only mandatory one — conventionally the largest assembly, the net opaque walls. Each entry is one component’s area over its resistance, in watts per kelvin, from an audit or the sibling delta page.
Component 2 UA
The second entry — typically the roof or ceiling plane, often the cheapest line to improve and a common leader of the ledger in older housing.
Component 3 UA
The third entry — typically the floor or slab perimeter, the line most often forgotten when the census is assembled from memory rather than drawings.
Component 4 UA
The fourth entry — typically the glazing, whose area must have been subtracted from the wall lines so the openings are not counted twice.
Component 5 UA
The fifth entry — typically the doors, a small area at a poor resistance, which is why the line is rarely negligible for its size.
Component 6 UA
The sixth entry — conventionally the infiltration line: air leakage expressed as an equivalent conductance so the moving-air loss sits in the same ledger as the fabric.
Component 7 UA
A spare line for a census that needs finer grain — a bay of curtain wall, a heated extension, a rim joist counted separately.
Component 8 UA
The last line of the ledger. A building needing more grain than eight entries is better served by grouping assemblies than by truncating them silently.
Assumptions and limits
- Components are independent parallel paths: thermal bridging where assemblies meet — studs into plates, slab edges, lintels — must already be inside each entry’s resistance, because the sum cannot add what the entries omit.
- Each UA is a steady-state, season-average figure; solar gain, wind-driven variation and hour-to-hour behaviour are averaged away before the ledger is written.
- Infiltration is folded in as one constant equivalent conductance, though real leakage varies with wind and stack effect across the season.
- The roll-up validates nothing about the census itself: a double-counted opening or a missing ceiling passes arithmetic that only an auditor can catch.
What the guards protect against
- A component count of zero is refused — the pack ships the refusal as a declared test vector — because a ledger with no lines has no total, and returning nothing-summed as an answer would dress an empty census up as a tight house.
- The count is capped at eight: entries beyond the cursor are ignored by construction rather than silently included, so a stale ninth line cannot haunt the total.
- Each entry is bounded far above any dwelling’s assembly, catching a whole-building figure pasted into a component line or a resistance entered where a conductance belongs.
Provenance
Envelope heat-transmission accounting: whole-building conductance as the sum of component UA values
Each participating component contributes its own conductance — area over resistance, with infiltration folded in as an equivalent — and the declared count masks entries beyond it before the parallel paths are summed into the whole-house total.
Screening and reference material, to be checked against the governing standard and a qualified engineer; not a design determination. The signed pack carries its own citation, which displays from the verified leaf when the calculator loads.