Compare unducted, exhaust-only, and fully ducted heat pump water heater layouts using electricity use, duct quotes, and yearly home HVAC cost changes.
The electricity rate is a 2025 U.S. planning estimate. Replace it with the usage rate from your local bill or utility provider.
Extra duct quotes
Yearly home HVAC cost change
Calculation details
Table of contents
How to use our Ducted vs Unducted Heat Pump Water Heater Cost Calculator
- Enter the selected water heater's HPWH yearly electricity use from its EnergyGuide label or product sheet.
- Replace Electricity usage rate with the marginal cents per kWh from your utility bill, then choose your Planning period.
- Enter separate installer quotes for Exhaust-only duct add-on cost and Fully ducted add-on cost.
- Enter each layout's yearly home HVAC cost change. Use a positive number for added cost and a negative number for avoided cost, then click Calculate.
- Check the layout costs above the lowest-cost choice. If a small change in a contractor's HVAC estimate changes the winner, ask for a more detailed estimate before choosing a layout.
Definitions
HPWH: Heat pump water heater. It moves heat from surrounding air to heat water.
HPWH yearly electricity use: The water heater's estimated electricity use over one year, measured in kWh/year.
Electricity usage rate: The per-kWh part of an electric bill, measured in cents/kWh. It does not include a fixed customer charge.
Home HVAC cost change: The estimated yearly change in heating and cooling cost caused by a layout. A positive value adds cost; a negative value reduces cost.
Exhaust-only: A layout that ducts air leaving the heat pump water heater while drawing intake air from the installation space.
Fully ducted: A layout that ducts both intake air and exhaust air for the heat pump water heater.
Duct add-on cost: One-time labor and material cost that is unique to a duct layout, beyond the shared water heater installation.
Common mistakes and quick fixes
Mistake: Entering whole-home electricity use in HPWH yearly electricity use.
Fix: Copy only the water heater's kWh/year value from its EnergyGuide label or product sheet.
Mistake: Using a monthly bill total as Electricity usage rate.
Fix: Enter the marginal usage rate in cents/kWh, not a fixed monthly customer charge.
Mistake: Combining both duct quotes in Exhaust-only duct add-on cost.
Fix: Put the exhaust-only quote in Exhaust-only duct add-on cost and the two-duct quote in Fully ducted add-on cost.
Mistake: Treating all yearly home HVAC cost changes as added costs.
Fix: In Unducted yearly home HVAC cost change, Exhaust-only yearly home HVAC cost change, and Fully ducted yearly home HVAC cost change, use a negative number when the layout is estimated to avoid cost.
Mistake: Choosing the lowest yearly cost without checking duct work.
Fix: Check HPWH yearly electricity use and then recalculate. Compare each selected-years water-heating and HVAC interaction cost, which includes its one-time duct add-on cost.
Limitations & Key Assumptions / Boundary Conditions
- The calculator compares only costs that differ by layout: water-heater electricity, the entered yearly home HVAC cost change, and layout-specific duct add-on cost.
- It assumes the same heat pump water heater and the same HPWH yearly electricity use for all three layouts.
- Yearly home HVAC cost changes are user estimates. They can vary with climate, home air leakage, duct design, installation location, heating equipment, cooling equipment, and how the water heater operates.
- Electricity prices are held constant across the Planning period. The calculation does not apply utility-price increases, inflation, discounting, maintenance, repairs, rebates, financing, or resale value.
- Fixed electric customer charges and common HPWH installation costs are excluded because they usually do not change among these layouts.
- A low-cost result does not confirm that a layout meets equipment instructions, duct sizing needs, airflow requirements, moisture control needs, or local code. Confirm the planned layout with a qualified installer.
Methodology
How the costs are calculated
The calculator first converts the entered HPWH yearly electricity use and Electricity usage rate into a yearly water-heater electricity cost.
yearly HPWH electricity cost = HPWH yearly electricity use x Electricity usage rate x 0.01
It then adds the separate home HVAC cost change entered for each layout.
yearly layout cost = yearly HPWH electricity cost + layout yearly home HVAC cost change
Each selected-years cost includes the yearly layout cost over the Planning period. Exhaust-only and fully ducted costs also include their one-time duct add-on costs. Unducted has no separate duct add-on input.
selected-years layout cost = yearly layout cost x Planning period + layout duct add-on cost
The lowest selected-years water-heating and HVAC interaction cost is the smallest of the three layout totals. Cost above the lowest-cost layout is that layout's total minus the smallest total.
cost above lowest = layout selected-years cost - lowest selected-years cost
Worked example
With 2,500 kWh/year and 17.3 cents/kWh, the yearly HPWH electricity cost is $432.50. If the unducted yearly home HVAC cost change is $70, its yearly combined cost is $502.50. Over 10 years, that is $5,025 with no duct add-on cost.
The 17.3 cents/kWh starting value is a 2025 U.S. planning estimate. Replace it with the marginal usage rate from your local bill or utility rate page. [1]