Seattle / Mercer Island
Mercer Island is about 7 miles from the Census center point for Seattle in a straight line and covers 6.383 square miles of land (Census 2024 Gazetteer internal points and land area, https://www2.census.gov/geo/docs/maps-data/data/gazetteer/2024_Gazetteer/, checked 2026-10-19).
Mercer Island has 25,307 residents (give or take 32) (ACS 2020-2024 5-year, table B01003, https://data.census.gov/table/ACSDT5Y2024.B01003?g=160XX00US5345005, checked 2026-10-19), about 3,965 people per square mile.
The quote form takes a ZIP code; for Mercer Island that is 98040 (Census 2020 ZCTA to county subdivision and ZCTA to place relationship files, ZIP areas at least 20% inside the town, https://www2.census.gov/geo/docs/maps-data/data/rel2020/zcta520/tab20_zcta520_cousub20_natl.txt and https://www2.census.gov/geo/docs/maps-data/data/rel2020/zcta520/tab20_zcta520_place20_natl.txt, checked 2026-10-19).
3,965 people per square mile puts Mercer Island in suburban density, where the outdoor unit usually sits in a side yard and the noise is not an issue for neighbors.
Of the 10,068 occupied homes in Mercer Island, 58% heat with natural gas, 1% with heating oil, 38% with electricity and 1% with propane (ACS 2020-2024 5-year, table B25040, https://data.census.gov/table/ACSDT5Y2024.B25040?g=160XX00US5345005, checked 2026-10-19).
Mercer Island has about the King County oil share of 2% and 17 points less electric heat than the county's 55% (ACS 2020-2024 5-year, table B25040, https://data.census.gov/table/ACSDT5Y2024.B25040?g=050XX00US53033, checked 2026-10-19).
Gas heats 58% of Mercer Island against electricity at 38%, so most quotes here are a partial-home system that carries the shoulder seasons and the summer while the gas furnace handles the coldest nights, or a whole-home system when the house is ready for it.
The median Mercer Island home was built in 1973 (ACS 2020-2024 5-year, table B25035, https://data.census.gov/table/ACSDT5Y2024.B25035?g=160XX00US5345005, checked 2026-10-19) and the median home has 7 rooms (ACS 2020-2024 5-year, table B25018, https://data.census.gov/table/ACSDT5Y2024.B25018?g=160XX00US5345005, checked 2026-10-19).
Mercer Island has 10,609 housing units, 3% built before 1940 and 61% before 1980, with 23% built in 2000 or later (ACS 2020-2024 5-year, table B25034, https://data.census.gov/table/ACSDT5Y2024.B25034?g=160XX00US5345005, checked 2026-10-19).
Mercer Island has 8 points fewer pre-1940 homes than King County as a whole (11%) and 7 points fewer homes built after 2000 than the county's 30% (ACS 2020-2024 5-year, table B25034, https://data.census.gov/table/ACSDT5Y2024.B25034?g=050XX00US53033, checked 2026-10-19).
61% of Mercer Island homes were built before 1980 and only 23% in 2000 or later (ACS 2020-2024 5-year, table B25034, https://data.census.gov/table/ACSDT5Y2024.B25034?g=160XX00US5345005, checked 2026-10-19), so most of the stock predates modern insulation codes; the installer's heat-loss calculation, not a square-footage rule, decides the tonnage.
67% of Mercer Island homes are single-family detached, 1% are in two- to four-unit buildings and 31% are in buildings of five or more units (ACS 2020-2024 5-year, table B25024, https://data.census.gov/table/ACSDT5Y2024.B25024?g=160XX00US5345005, checked 2026-10-19).
33% of Mercer Island homes are rented (ACS 2020-2024 5-year, table B25003, https://data.census.gov/table/ACSDT5Y2024.B25003?g=160XX00US5345005, checked 2026-10-19), so beside the 67% detached houses there is a real share of jobs where the landlord, not the resident, signs the quote.
Mercer Island has 17 points more detached houses than King County overall (50%) (ACS 2020-2024 5-year, table B25024, https://data.census.gov/table/ACSDT5Y2024.B25024?g=050XX00US53033, checked 2026-10-19).
No electric utility is on file for Mercer Island on this door yet, so this page does not name one; the name on the bill decides which rebate path applies.
PSE heat pump rebates (electric resistance to ASHP conversion), run by Puget Sound Energy, is a live program for Washington addresses and covers qualifying equipment at $2,400 per system (registry row 14 verified 2026-10-14, https://www.pse.com/en/rebates/heating/electric-resistance-to-air-source-heat-pump-conversion-rebate, checked 2026-10-16); confirm eligibility for the Mercer Island address before counting it. With 38% of Mercer Island homes already on electric heat and 60% on gas, oil or propane, the row that applies depends on the name on the electric bill and the fuel coming out.
Seattle City Light heat pump instant discounts, run by Seattle City Light, is a live program for Washington addresses and lists a standard figure of $300 (registry row 47 verified 2026-10-16, https://seattle.gov/city-light/residential-services/home-energy-solutions/heating-and-cooling-your-home, checked 2026-10-16); confirm eligibility for the Mercer Island address before counting it.
Seattle Clean Heat Program (oil to heat pump), run by City of Seattle Office of Sustainability and Environment, is a live program for Washington addresses and lists a standard figure of $2,000 (registry row 48 verified 2026-10-14, https://seattle.gov/environment/climate-change/buildings-and-energy/seattles-clean-heat-program, checked 2026-10-16); confirm eligibility for the Mercer Island address before counting it.
Median household income in Mercer Island is $219,069 (ACS 2020-2024 5-year, table B19013, https://data.census.gov/table/ACSDT5Y2024.B19013?g=160XX00US5345005, checked 2026-10-19); many state and utility heat pump rebate programs set higher incentive tiers for income-qualifying households, so the household income on the application, not the town median, decides which level applies.
Heating design temperature: 11F. Source: ENERGY STAR Design Temperature Limit Reference Guide (2019 Edition), King County row, 99% heating, PDF pages 133 to 135 of 141 (Revised 11/11/2020), https://www.energystar.gov/sites/default/files/Design%20Temperature%20Limit%20Reference%20Guide%20(2019%20Ed)%20-%20ENERGY%20STAR%20Single-Family%20New%20Homes_Rev11.pdf, fetched 2026-10-19, 99%.
That 11F figure is the King County cold-day number a Mercer Island heat pump is sized against, so ask the installer to show the system's heating output at 11F, not at the milder rating-label temperature.
Ask whether the quote is whole-home or partial-home, because with 58% of Mercer Island on gas and 38% already electric the two paths carry different rebate figures and different sizing.
Ask for the heat-loss calculation room by room; the median Mercer Island home has 7 rooms and was built around 1973, and the count of heads and the tonnage follow the rooms and the insulation, not the square footage.
The form on this page is the follow-up for Mercer Island. The public number is the number the contractor quotes from.
No local contractor is named on this door for Mercer Island yet. A request from this page goes to the first licensed shop that takes the door.