12 Heat Loss Sources in a Typical Massachusetts Home (Ranked by Impact).

The 12 Heat Loss Sources, Ranked

Ranking based on average MA single-family blower door + thermal imaging data. Percentages = share of total heating energy loss.

1. 01

   Attic insulation gaps + air leakage (25-35%)

   The single biggest heat loss source in pre-1990 MA homes. Heat rises; if attic is under-insulated (R-19 or less) with air leakage at the ceiling-attic plane (recessed lights, attic hatch, plumbing chases), the loss compounds. Remediation: R-49 attic insulation + air sealing = $4,800-$6,200 gross, $0-$1,400 net after Mass Save rebate.

2. 02

   Rim joist + basement perimeter (10-15%)

   The band joist where the floor framing sits on the foundation wall. Often uninsulated and air-leaky. Cold air enters; warm air exits. Remediation: closed-cell spray foam at rim joist = $1,400-$2,800 gross, $0-$700 net after Mass Save.

3. 03

   Wall infiltration through electrical outlets + plumbing penetrations (8-12%)

   Each wall outlet, switch, plumbing penetration leaks 5-15 CFM at 50 Pa. 30 outlets = 150-450 CFM50 of infiltration. Remediation: foam outlet gaskets ($1-$3 each) + caulk plumbing penetrations from inside basement = $80-$200 in materials, DIY-able.

4. 04

   Single-pane windows or failed double-pane seals (15-20%)

   Single-pane: U-1.0 to U-1.2. Failed double-pane (broken seal, fog between panes): U-0.6 to U-0.8. Modern replacement (U-0.27 stretch code): U-0.27. Remediation: window replacement = $580-$1,400 per window installed, with Mass Save Energy Star rebate $50-$120/window.

5. 05

   Doors (exterior + door-to-garage) (3-5%)

   Air leakage at door bottom sweep, door jamb, threshold. Worse on older fiberglass or solid wood doors with degraded weatherstripping. Remediation: weatherstripping replacement ($30-$80 per door, DIY) or door replacement ($800-$2,400 per door).

6. 06

   Ductwork in unconditioned spaces (5-10%)

   Ducts in unconditioned attic or basement leak conditioned air to outside the heated envelope. Pre-1990 ducts in MA commonly leak 25-40% of air volume. Remediation: duct sealing with mastic + insulation wrap = $800-$2,400, with Mass Save rebate.

7. 07

   Fireplace flue (open-flue when not in use) (5-10%)

   An open damper on an unused fireplace exhausts warm room air up the chimney 24/7. Loss can exceed 10% of heating energy on a chronically-open damper. Remediation: tight-fitting damper + glass doors = $200-$800 DIY or $400-$1,400 installed.

8. 08

   Recessed lights penetrating attic (3-5%)

   Each non-IC-rated recessed light leaks ~10 CFM at 50 Pa into the attic. 8 cans in a typical kitchen ceiling = 80 CFM50. Remediation: air-tight covers in attic above each can = $30-$60 per fixture installed.

9. 09

   Bath fan / range hood ductwork to exterior (2-4%)

   Bath fans and range hoods that vent to exterior leak warm air OUT through the duct when not in use (no backdraft damper) and IN cold outside air. Remediation: install backdraft dampers + duct insulation = $80-$280 per fan.

10. 10

    Foundation walls (basement) (3-6%)

    Concrete or block foundation walls with no interior insulation conduct heat directly to the soil. Remediation: rigid foam board on basement wall interior + drywall finish = $4-$8 per sq ft, with Mass Save rebate.

11. 11

    Floor over unheated garage / crawl space (3-5%)

    Floor framing exposed to unheated garage or crawl space loses heat downward. Remediation: R-30 fiberglass batts between floor joists from below = $1,200-$2,800 typical garage ceiling area, with Mass Save rebate.

12. 12

    Whole-house exhaust without HRV (2-4%)

    Mechanical ventilation per ASHRAE 62.2 exhausts warm air; if no Heat Recovery Ventilator (HRV/ERV) is installed, that warm air leaves with no recovery. Remediation: HRV install $2,400-$4,800 — pays back over 8-15 years on heating savings + IAQ improvement.

Where to Spend the First $2,000

Best ROI for MA homeowners on first $2,000 of weatherization budget:

1. Mass Save HEA ($0): Establishes baseline, identifies priorities, unlocks rebates. Always step 1.
2. Air sealing pass ($1,800-$3,200 gross, $0-$800 net): Top-plate, rim joist, recessed lights, plumbing chases. Highest impact per dollar.
3. Attic insulation R-49 upgrade ($3,800-$5,400 gross, $0-$1,200 net): Combined with air sealing in same project. Largest single source addressed.
4. Outlet/switch foam gaskets ($80-$200 DIY): Cheapest impact possible; 30 minutes work; immediate comfort improvement on exterior walls.

For the full Mass Save rebate sequencing across all 12 sources, see our whole-home electrification roadmap.