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A Wellesley homeowner planned heat pumps and future solar as one electrification roadmap. NuWatt sized the heat pump, modeled the new electric load, and translated expected heating kWh into a future solar system size.
Solar should be sized with heat pump load in mind. This Wellesley case used a 4-ton ducted heat pump design, dual-fuel backup, Mass Save planning, and a solar sizing model that accounted for future heating electricity. That prevents undersizing solar before electrification.
| Category | Project Detail | Why It Matters |
|---|---|---|
| Home type | 1990s colonial, 3,100 sq ft | Sets the envelope, duct, and zoning constraints. |
| Previous heating | Gas furnace and central AC | Determines fuel-switching economics and backup strategy. |
| Equipment | Bosch IDS ducted heat pump with solar sizing plan | Cold-climate equipment selection affects winter performance. |
| Capacity and zones | 4 tons, 2 zones | Shows whether the project is room-level or whole-home. |
| Rebate pathway | Partial-home or whole-home pathway depending on fossil backup controls | Rebate rules vary by state, utility, equipment, and project scope. |
| Cost range | $27,000-$36,000 before rebates | Useful for comparing quote reasonableness. |
| Net cost range | $18,500-$27,500 after standard rebate target | Shows cost after standard rebate target, before final approval. |
| Estimated savings | $1,200-$2,100 before solar offset | Modeled operating-cost impact, not a guarantee. |
Installing solar first using old electric bills would have undersized the future solar array.
Replacing AC with a heat pump was timely, but full gas removal was not required immediately.
The homeowner needed a single plan for Mass Save, electric load growth, and solar economics.
Duct performance had to be checked before reusing the existing central distribution.
NuWatt designed a ducted heat pump that reused suitable ductwork and retained gas backup through dual-fuel controls.
The proposal included post-heat-pump kWh modeling so the solar system could be sized for the future home, not the past bill.
Mass Save eligibility was reviewed separately from solar economics to keep incentives clean.
The homeowner received a sequencing plan: heat pump first, solar sizing second, battery readiness optional.
| Decision | Reason | Field Note |
|---|---|---|
| Model future electric load | Solar sized from pre-heat-pump bills would miss the new heating consumption. | Electrification planning should connect HVAC design and solar design. |
| Use dual-fuel backup | The gas furnace was serviceable and the homeowner wanted resilience during transition. | Dual-fuel can be a pragmatic step when full electrification is not the first priority. |
| Reuse ducts only after review | Existing ducts can work, but leakage and sizing can limit performance. | Duct review is essential before promising central heat pump comfort. |
Ducted dual-fuel design.
Upstairs and downstairs balancing.
Depends on approved Mass Save pathway.
Estimated future heating load for PV sizing.
Before potential solar offset.
Ducted equipment replacement.
Manual J and future heating kWh estimate.
Checked distribution feasibility, zoning, and return-air constraints.
Outdoor unit, indoor coil/air handler integration, controls, and backup setup.
Post-heat-pump load estimate prepared for solar design.
Final costs, rebates, and savings require a site-specific quote, utility confirmation, equipment selection, home energy assessment, and Mass Save approval.
If both are planned, model the heat pump load before final solar sizing. Installing solar from old electric bills can undersize the system for the electrified home.
Yes. Solar can offset annual heat pump electricity use, though winter production is lower than summer. Good planning uses annual kWh plus seasonal expectations.
Sometimes. Existing ducts should be reviewed for sizing, leakage, insulation, returns, and airflow before a ducted heat pump is promised.
Mass Save covers eligible heat pump work, not solar. Solar has separate economics and incentives. The two should be planned together but documented separately.
Dual-fuel can be useful when the existing gas furnace is in good condition or the homeowner wants backup. Full savings depend on lockout settings and fuel prices.