Of 31 Massachusetts municipal sources in this dataset, only 10 keep records capable of answering a simple question: when a household replaces its heating system, is the replacement a heat pump? In those 10 towns, across 550 heating permits, the answer is 31.1%.
The disqualification is the story. Three of the largest sources here - Worcester, Cambridge, Lexington - had to be excluded, and the reason is worth more than the ranking. They file fossil-fuel heating work under a fixed category label instead of a description. Search their text for "boiler" or "furnace" and you find almost nothing; search it for "heat pump" and you find everything. Ranked naively, Lexington comes out at 94% heat pump and Worcester at 0%. Both numbers are false, and both are about filing conventions rather than heating.
Mansfield leads at 44.2% of heating permits; West Bridgewater sits at 13.8%. That is a 3.2x spread between towns in the same state under the same building code and the same rebate program - which is the genuinely interesting result, and a much smaller number than an ungated analysis would have produced.
| Town | Heating permits | Heat pump | Share |
|---|---|---|---|
| Mansfield | 77 | 34 | 44.2% |
| Randolph | 72 | 30 | 41.7% |
| Hingham | 38 | 15 | 39.5% |
| Milton | 59 | 22 | 37.3% |
| Hanson | 34 | 11 | 32.4% |
| Rockland | 55 | 16 | 29.1% |
| Braintree | 96 | 21 | 21.9% |
| Falmouth | 47 | 10 | 21.3% |
| Taunton | 43 | 8 | 18.6% |
| West Bridgewater | 29 | 4 | 13.8% |
These sources carry 449 heating permits between them - nearly as many as the entire eligible sample of 550 - and none of it is usable for this question. The "distinctness" column is the test: it is the fraction of a town's gas-fitting permits carrying a distinct description. At 0.01, a town is filing nearly every gas job under the same handful of words.
| Town | Heating permits | Would have reported | Description distinctness |
|---|---|---|---|
| Worcester | 299 | 0.0% | 0.01 |
| Cambridge | 97 | 85.6% | 0.05 |
| Lexington | 53 | 94.3% | 0.01 |
A source is eligible only if its gas-fitting permits carry distinct descriptions on at least 50% of rows, and it has at least 20 classified heating permits. Nobody working from a single town's data could discover that their own records are unable to answer this - it only shows up by comparing description entropy across towns.
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In Massachusetts towns whose permit records describe the work, what share of heating-system permits are heat pumps?
Rows whose description is at least 8 characters, matched against two rules. Heat pump: heat\s*pump|mini[\s-]?split|minisplit|ductless|\bashp\b. Fossil fuel: \bfurnace(s)?\b|\bboiler(s)?\b|forced hot air|\bgas heat\b|oil burner. Heat pump wins a tie. 550 rows classified across eligible sources.
10 sources, each with at least 20 classified heating permits and gas-permit description distinctness of at least 0.50.
3 sources carrying 449 heating permits, named in the table above with the distinctness figure that disqualified each. A further 18 sources had too few classified heating rows to rank and are not listed, because a share computed on a handful of rows is noise.
Description text is a proxy for the appliance actually installed. A permit reading 'replace heating system' with no further detail is counted in neither direction, and a town that describes heat pumps more enthusiastically than boilers would shift its own number.
Computed 2026-08-18 from a dataset fetched 2026-09-06. Download the figures behind this page (JSON).
In the 10 towns whose records can answer, 31.1% of 550 heating-system permits are heat pumps, mini-splits or ductless systems. Town-level shares run from 13.8% to 44.2%.
Those towns file fossil-fuel heating work under a fixed category label rather than a description, so a text search finds their heat pumps but not their boilers. Including them would have reported one town at 100% heat pump and another at 0%, both false.
No. It is the heat-pump share of permits in ten towns whose records are legible for this question, and those towns were selected by record quality rather than by being representative of Massachusetts.
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