HVAC Calculator
Calculate BTU cooling/heating loads, size heat pumps with IRA 25C credit checks, and find the solar panel count needed to power your HVAC system — free, no signup.
HVAC Load & Heat Pump Calculator
Calculate BTU cooling/heating loads by IECC climate zone, size a heat pump with federal efficiency checks, and find the solar panel count needed to power your HVAC system.
Ready to design solar projects
in minutes, not hours?
SurgePV combines AI-powered 3D roof modeling, bankable energy simulation, and white-label proposals in one platform. Used by solar installers to close deals faster.
What This HVAC Calculator Covers
Three calculators in one tool - covering the full HVAC sizing and solar offset workflow. No signup required.
BTU Load Calculator
Calculates cooling and heating loads from square footage, ceiling height, insulation, window area, sun exposure, and occupant count. References IECC climate zones mapped to 45 US cities.
Heat Pump Sizing
Compares current HVAC operating costs vs a new heat pump, checks federal SEER2/HSPF2 efficiency minimums, and shows IRA 25C tax credit eligibility for units installed before 12/31/2025.
Solar for HVAC
Calculates the number of solar panels and total system size (kW) needed to offset HVAC electricity consumption, accounting for system efficiency and panel wattage.
Key Features
Built for homeowners, solar installers, and HVAC contractors who need accurate load estimates and solar offset numbers fast.
IECC Climate Zone Lookup
45 US cities pre-mapped to IECC zones 1–8. Each zone has a calibrated BTU/sqft base load and seasonal operating hours.
Multi-Factor Load Multipliers
Adjusts base BTU for ceiling height (8–12 ft), insulation level, window area, sun exposure, and number of occupants - all configurable sliders.
Federal Efficiency Compliance Check
Flags whether a heat pump meets the 2023 federal minimums - SEER2 ≥ 15.2 (North) / 15 (South) and HSPF2 ≥ 8.8.
IRA 25C Tax Credit Check
Shows IRA 25C credit eligibility and dollar amount for qualifying heat pumps - $2,000 max for units meeting efficiency thresholds (installations before 12/31/2025).
Old vs New Cost Comparison
Calculates annual operating cost for the current system and a new heat pump, then shows the annual savings - factoring in local utility rate and COP.
Solar Panel Count Output
Converts HVAC electricity consumption to solar panel count and total kW system size - with a configurable panel wattage input and 78% system efficiency factor.
How to Use This Calculator
Three independent modes - use them in sequence or jump straight to the one you need.
BTU Load Calculator - enter your home details
Select your city (or nearest city) to auto-assign the IECC climate zone. Enter square footage, ceiling height, insulation quality, window area percentage, sun exposure, and number of occupants. The tool applies zone-specific BTU/sqft rates and multipliers to output cooling and heating loads in BTU/hr.
Heat Pump Sizing - compare current vs new system
Enter your current system's efficiency (SEER/HSPF), the proposed heat pump's SEER2 and HSPF2 ratings, your local electricity rate, and the heat pump's purchase/install cost. The tool calculates annual operating cost for both systems, annual savings, simple payback period, and whether the unit qualifies for the IRA 25C tax credit.
Solar for HVAC - find your panel count
Enter your HVAC system's annual electricity consumption (kWh) and panel wattage. The calculator divides consumption by system efficiency (78%) to find required generation, then divides by panel output to get panel count and total system size in kW.
IECC Climate Zones & BTU Benchmarks
The BTU Load Calculator uses these IECC zone benchmarks. Zones 1–3 are hot/warm climates; zones 5–8 are cold climates where heating loads dominate.
| IECC Zone | Climate Description | Base Cooling BTU/sqft | Base Heating BTU/sqft | Example Cities |
|---|---|---|---|---|
| Zone 1 | Very Hot / Humid | 30 | 15 | Miami, Honolulu |
| Zone 2 | Hot / Dry or Mixed | 28 | 18 | Phoenix, Houston, New Orleans |
| Zone 3 | Warm / Mixed | 24 | 20 | Atlanta, Dallas, Los Angeles |
| Zone 4 | Mixed / Moderate | 20 | 25 | Washington DC, St. Louis, Seattle |
| Zone 5 | Cool / Mixed | 16 | 30 | Chicago, Denver, Boston |
| Zone 6 | Cold | 12 | 35 | Minneapolis, Burlington |
| Zone 7 | Very Cold | 8 | 40 | Duluth, Fairbanks |
| Zone 8 | Subarctic | 5 | 50 | Anchorage |
BTU/sqft values are base rates before multipliers for ceiling height, insulation, window area, sun exposure, and occupants. Heating loads include a 0.70 seasonal factor.
Calculation Methodology
Transparent formulas so you can verify outputs and explain them to clients.
BTU Load Formula
Cooling BTU = sqft × zone_cooling_rate × ceiling_mult × insulation_mult × window_mult × sun_mult × occupant_mult
Heating BTU = sqft × zone_heating_rate × ceiling_mult × insulation_mult × window_mult × 0.70 (seasonal factor)
The 0.70 seasonal factor reflects that heating systems run at full load only during peak cold periods. Divide BTU/hr by 12,000 to convert to tons of cooling.
Heat Pump Operating Cost Formula
Annual kWh = (BTU_load × hours_per_year) / (efficiency × 3,412)
Annual Cost = Annual kWh × utility_rate
3,412 BTU = 1 kWh. SEER2 applies to cooling; HSPF2 applies to heating. The tool sums both seasonal costs to get total annual operating cost.
Solar Panel Count Formula
Required Generation (kWh) = HVAC consumption / 0.78
Annual Panel Output (kWh) = panel_watt × peak_sun_hours × 365 / 1000
Panel Count = Required Generation / Annual Panel Output
The 78% system efficiency accounts for inverter losses, wiring losses, and soiling. Peak sun hours default to 4.5 hours/day - a conservative national average for the continental US.
Who Uses This Tool
Useful at every stage of the HVAC + solar project lifecycle.
Solar Installers Adding HVAC Offset
Use the Solar for HVAC mode to show customers exactly how many additional panels they need to fully power their air conditioning. It makes upsell conversations data-driven - "your AC uses 4,200 kWh per year; 5 panels covers that."
- Quantify HVAC offset in panel count and kW
- Build a stronger proposal narrative
- Combine with the Electricity Bill Calculator to show full load offset
HVAC Contractors Recommending Heat Pumps
Show clients their current system's annual cost vs a new heat pump, flag whether the unit meets federal efficiency standards, and calculate IRA 25C credit eligibility - all in one conversation.
- Instant cost comparison - old system vs new
- Verify SEER2/HSPF2 federal compliance
- Flag IRA 25C tax credit opportunity
Homeowners Planning an Upgrade
Before calling a contractor, run the BTU Load Calculator to know roughly what size system you need. Then use the Heat Pump Sizing mode to understand if a heat pump makes financial sense given your utility rate.
- Independent BTU estimate before contractor visit
- Understand heat pump payback period
- Know the federal tax credit before shopping
Energy Auditors & Consultants
Quickly sanity-check Manual J estimates or produce preliminary load numbers during an energy audit. The IECC zone + multiplier approach is conservative and works well for early-stage assessments before a full Manual J is warranted.
- Fast preliminary load estimate
- Climate-zone-based benchmarking
- Solar offset recommendation included
Heat Pump vs. Traditional AC: Key Differences
Understanding the efficiency difference explains why heat pumps change the solar offset math - and the IRA credit eligibility.
| Factor | Heat Pump | Traditional AC + Gas Furnace |
|---|---|---|
| Cooling Efficiency | SEER2 15–25+ | SEER 13–18 (legacy units) |
| Heating Source | Electricity (COP 2–4) | Natural gas - separate appliance |
| Federal Efficiency Standard | SEER2 ≥ 15.2 (N), HSPF2 ≥ 8.8 | SEER2 ≥ 14.3 (N), 15.2 (S) |
| IRA 25C Tax Credit | Up to $2,000 if qualifying SEER2/HSPF2 | Not eligible for heat pump credit |
| Solar Offset Needed | Covers all heating too - larger solar offset | Only cooling is electric - smaller solar offset |
| Emissions | Zero direct - lower if grid is clean or solar-powered | Direct gas combustion for heating |
Pro Tips
Combine BTU mode with Heat Pump mode in sequence
Run the BTU Load Calculator first to get your cooling and heating loads. Then carry those numbers into the Heat Pump Sizing mode - the BTU load drives the operating hours calculation that determines annual kWh and cost.
The IRA 25C credit expired December 31, 2025
The Inflation Reduction Act's 25C credit for heat pumps (up to $2,000) applied to qualifying installations made through 12/31/2025. The tool flags eligibility based on that deadline - consult a tax advisor for the latest guidance before filing.
Use a conservative peak sun hour figure for HVAC-only solar sizing
The Solar for HVAC mode defaults to 4.5 peak sun hours/day. In hot zones (1–3) where AC dominates, summer irradiance is higher - you can adjust up to 5.5–6 hours for Phoenix or Miami. In zones 5–7 where heating is the main load, the 4.5 default is appropriate.
This is a preliminary estimate - not a substitute for Manual J
ACCA Manual J is the ANSI-approved method for residential load calculations required by most building codes. This tool uses IECC zone benchmarks and multipliers for speed - accurate enough for early-stage proposals and customer conversations, but confirm with a full Manual J before permit submission.
Frequently Asked Questions
How accurate is this BTU calculator vs Manual J?
What does SEER2 vs SEER mean?
How many solar panels does a typical AC unit need?
Is the IRA 25C credit still available in 2026?
What's the difference between tons and BTU?
Can I use this for commercial HVAC sizing?
Related Tools
Electricity Bill Calculator
Identify energy hogs and find the solar size to offset your bill.
CO2 Savings Calculator
Calculate carbon footprint and CO₂ saved by going solar.
Battery Sizing Calculator
Size battery storage to back up your home's critical loads.
AC Size Calculator
Size NEC 690-compliant AC output circuits for solar systems.
Ready to Build the Solar + HVAC Proposal?
SurgePV takes your HVAC load estimate and turns it into a complete solar proposal - system design, shading analysis, financial modeling, and e-signatures in one platform.
No credit card required · Full access · Cancel anytime
