HVAC VFD Payback Calculator

VFDs cut motor energy 30-60% by varying speed to demand vs constant-speed operation.

Motor HP

Run hours / yr

VFD + install cost

$/kWh

Average load reduction %

Rebate

Payback years

0.4

Annual savings

$16,114

kWh saved / yr

134,280

How the math works

kWh saved = HP × 0.746 × run hrs × load reduction. Savings = kWh × rate.

75 × 0.746 × 6,000 × 40% = 134,280 kWh × $0.12 = $16,114/yr. Net $6k. 0.4 yr!

How to Use

Enter motor HP.
Enter run hours per year.
Enter VFD cost.
Enter electricity rate.
Enter expected load reduction %.
Read payback.

Frequently Asked Questions

VFD basics?

Constant-speed motor runs 100% always, throttled by valves/dampers. VFD (Variable Frequency Drive) adjusts motor speed to match demand. Energy savings cubic with speed: 80% speed = 51% power (80^3). 60% speed = 22% power. Best applications: centrifugal pumps, fans with variable load. Typical savings: 30-60% on retrofit.

Cost and payback?

Small VFD (5-50 HP): $1,500-6,000 each + installation $500-2,000. Medium (50-200 HP): $6,000-25,000. Large (200-800 HP): $25,000-100,000. Typical 100 HP motor running 6,000 hrs/year: saves 150,000-300,000 kWh/year with VFD = $18-36k annual savings. Payback 1-4 years typical for retrofits.

Utility rebates?

Prescriptive VFD rebates: $40-150 per HP. Custom rebates: $0.08-0.20/kWh saved. Energy audit may be required. Deep retrofit programs stack VFDs with controls + commissioning = 20-40% total building energy reduction. 179D deduction: qualifies as mechanical system retrofit in 179D calculations.

Best applications?

(1) Chilled water pumps (largest savings, 40-60%). (2) Cooling tower fans (20-50% savings). (3) Supply/return air fans (30-50%). (4) Hot water circulation pumps (30-45%). (5) Heating hot water pumps (25-40%). Constant-flow systems that historically throttled with valves/dampers: excellent VFD candidates. Poor candidates: positive displacement pumps, already-efficient 2-speed motors.