Free HVAC Calculators — Sizing, Airflow, Efficiency & Cost
Every HVAC calc a job needs — sizing, efficiency, and cost — in one place: cooling load in BTU, system size in tons, heat pump and ductless mini-split sizing, furnace size with AFUE efficiency, airflow in CFM, duct diameters, the savings of a higher SEER or AFUE rating, what it costs to run and to replace a system, and how to price the whole job. Each tool is free, instant, and explains its formula in plain English with worked examples.
Sizing
Find the right system for any space — cooling load, heating load, tonnage, heat pump sizing, and electrical and gas service requirements.
HVAC BTU Calculator
The full cooling load for any room or home — adjusted for climate, sun exposure, insulation, ceiling height, and occupancy.
Answers: "What size AC do I need for 1,500 sq ft?"
Open calculatorManual J Load Calculation Calculator
Whole-home heating and cooling load in BTU and tons — from square footage, climate zone, insulation, ceiling height, and sun exposure.
Answers: "What is my home's Manual J heating and cooling load?"
Open calculatorAC Tonnage Calculator
Convert BTU to tons and back instantly, estimate tonnage from square footage, and decode the size hidden in any unit's model number.
Answers: "How many tons is 36,000 BTU?"
Open calculatorAC Tonnage per Square Foot
How many tons of AC a home needs by square footage and climate — with a square-footage-to-tonnage chart and the tons-per-sq-ft rule.
Answers: "How many tons of AC per square foot?"
Open calculatorHVAC Unit Converter
Convert HVAC units in the field — tons to BTU/h and kW, Fahrenheit to Celsius, inches of water column to Pascals, and PSI to kPa.
Answers: "How many BTU is 3 tons?"
Open calculatorFurnace BTU Calculator
Heating load by climate zone and insulation, converted into the furnace input size to buy using AFUE efficiency.
Answers: "What size furnace for a 2,000 sq ft house?"
Open calculatorHeat Pump Sizing Calculator
Size a heat pump for both heating and cooling — BTU and tonnage by climate zone, insulation, and ceiling height, with cold-climate balance-point guidance.
Answers: "What size heat pump do I need?"
Open calculatorMini-Split Sizing Calculator
Find the right BTU size for a ductless mini-split — per room or multi-zone — adjusted for insulation, climate, ceiling height, sun, and kitchen heat.
Answers: "What size mini-split do I need?"
Open calculatorHeat Loss Calculator
Whole-home heating load from climate zone, square footage, insulation level, and window area — the heating counterpart to the BTU cooling load calculator.
Answers: "How many BTU of heat does my home lose per hour?"
Open calculatorHVAC Amp Draw Calculator
Estimate running amperage, minimum circuit ampacity (MCA), and maximum overcurrent protection (MOP) from system BTU/h, SEER2 rating, and supply voltage.
Answers: "What size breaker do I need for a 3-ton AC?"
Open calculatorGas Line Sizing Calculator
Pipe diameter for natural gas or LP lines from BTU/h load and pipe length — from IFGC/NFPA 54 Table 402.4 pressure-drop values.
Answers: "What size gas pipe for a 200,000 BTU furnace at 50 feet?"
Open calculatorAirflow & Ductwork
Calculate CFM requirements, select duct diameters, apply fan affinity laws, and verify Manual D friction rates.
HVAC CFM Calculator
Room airflow from volume and air changes per hour, plus the total system CFM target from tonnage (350–450 CFM per ton).
Answers: "How many CFM does this room need?"
Open calculatorDuct Size Calculator
Convert CFM into the round duct diameter you need — sheet metal or flex — with a velocity check and full sizing chart.
Answers: "What size duct for 400 CFM?"
Open calculatorFan Laws Calculator
Apply fan affinity laws to predict CFM, static pressure, and brake horsepower when blower RPM changes.
Answers: "What happens to CFM if I slow the blower 10%?"
Open calculatorDuct Friction Rate Calculator
Manual D available static pressure and design friction rate — from equipment ESP, component losses, and total effective duct length. Flags high-velocity and oversized-ductwork conditions.
Answers: "What is the Manual D friction rate for my system?"
Open calculatorDiagnostics & Refrigerant
Check temperature splits, total external static pressure, refrigerant charge, PT chart lookup, and boiler combustion efficiency.
Delta T Calculator
Check an AC temperature split (return minus supply, normally 16–22°F) or furnace temperature rise — and what a high or low reading means.
Answers: "What is a good Delta T for an AC?"
Open calculatorStatic Pressure Calculator
Add supply and return static pressure readings to get total external static pressure (TESP) and compare it to the equipment's rated maximum.
Answers: "What should total static pressure be?"
Open calculatorSuperheat Calculator
Calculate measured superheat from suction line temperature and saturation temperature, with TXV and fixed-orifice target guidance.
Answers: "What should superheat be on my AC?"
Open calculatorSubcooling Calculator
Calculate measured subcooling from liquid saturation temperature and liquid line temperature, with TXV charging targets.
Answers: "What should subcooling be on my AC?"
Open calculatorTarget Superheat Calculator
Find the target superheat for a fixed-orifice system from indoor wet-bulb and outdoor dry-bulb temperatures.
Answers: "What is the target superheat for a piston meter?"
Open calculatorRefrigerant Charge Calculator
Calculate line-set add-on refrigerant charge beyond the factory allowance — by refrigerant type, line diameters, and total run length.
Answers: "How much refrigerant do I add for extra line set?"
Open calculatorCombustion Efficiency Calculator
Boiler stack loss and net combustion efficiency using the Siegert formula — from flue gas temperature, combustion air temperature, and flue oxygen percentage.
Answers: "What is my boiler's combustion efficiency?"
Open calculatorRefrigerant PT Chart
Saturation pressure–temperature reference for R-410A, R-32, R-454B, and R-22 — look up by temperature or pressure with phase-state indication.
Answers: "What is the saturation pressure of R-410A at 40°F?"
Open calculatorPsychrometrics & Indoor Air Quality
Dew point, sensible and latent heat, mixed air temperature, ASHRAE ventilation, humidity sizing, HRV/ERV effectiveness, and full moist-air properties.
Dew Point Calculator
Find dew point from dry-bulb temperature and relative humidity (or RH from dew point), with condensation-risk flags for ducts and surfaces.
Answers: "What is the dew point at 75°F and 55% RH?"
Open calculatorSensible & Latent Heat Calculator
Split total coil load into sensible and latent BTU/h from CFM, temperature change, and humidity ratio change — plus sensible heat ratio (SHR).
Answers: "How much latent heat is my coil removing?"
Open calculatorMixed Air Temperature Calculator
Mixed air temperature from outdoor and return CFM and temperatures — for economizer design, AHU commissioning, and outdoor air fraction.
Answers: "What is the mixed air temperature at 20% outside air?"
Open calculatorVentilation Calculator
Size whole-building ventilation CFM using ASHRAE 62.2 residential rates or ASHRAE 62.1 commercial people-and-area rates.
Answers: "How much ventilation CFM does my home need?"
Open calculatorHumidity Control Calculator
Size a humidifier or dehumidifier from indoor RH targets, room volume, and airflow — latent load in BTU/h, pints/day, or gallons/day.
Answers: "What size dehumidifier do I need?"
Open calculatorHRV / ERV Effectiveness Calculator
Sensible heat recovery effectiveness (ASHRAE 84) from supply and exhaust airflow and temperatures — with flow imbalance and thermodynamic limit warnings.
Answers: "What is my HRV sensible effectiveness?"
Open calculatorACH Ventilation Calculator
Convert CFM to air changes per hour (or reverse) and check against ASHRAE 62.1, 62.2, and 170 minimum rates for offices, restrooms, healthcare, and residential spaces.
Answers: "How many air changes per hour does this room have?"
Open calculatorPsychrometric Calculator
All eight moist-air properties from dry-bulb temperature and relative humidity: humidity ratio, specific enthalpy, dew point, wet-bulb temperature, vapour pressure, specific volume, and air density.
Answers: "What is the enthalpy and humidity ratio of 75°F, 50% RH air?"
Open calculatorEfficiency & Cost
Compare SEER/SEER2, HSPF, and AFUE ratings, calculate operating cost and replacement cost, size hydronic systems, and price contractor jobs.
SEER Savings Calculator
Compare two SEER ratings and see annual electricity use, yearly cost, and the 15-year savings of the more efficient unit.
Answers: "Is SEER 16 worth it over SEER 14?"
Open calculatorSEER / SEER2 Converter
Convert between SEER and SEER2 efficiency ratings, compare to 2023 federal minimum standards, and see how the test-procedure change affects real-world comparisons.
Answers: "What is SEER 16 in SEER2?"
Open calculatorHSPF Savings Calculator
Compare two heat pump HSPF ratings and see annual heating electricity use, yearly cost, and 15-year savings of the more efficient unit.
Answers: "Is HSPF 10 worth it over HSPF 8?"
Open calculatorAFUE Savings Calculator
Compare two furnace AFUE ratings and see the annual fuel cost, dollar savings, and 15-year payoff of a higher-efficiency furnace.
Answers: "Is a 95% AFUE furnace worth it?"
Open calculatorHVAC Operating Cost Calculator
What it actually costs to run your AC, heat pump, or furnace — per hour, per day, and per year — from efficiency, runtime, and energy price.
Answers: "How much does it cost to run my AC?"
Open calculatorReplacement Cost Calculator
Installed price range for a new AC, furnace, heat pump, or full system — by size, efficiency tier, ductwork, and region.
Answers: "How much does a new HVAC system cost?"
Open calculatorDuctwork Replacement Cost Calculator
Estimate the installed cost to replace home ductwork — by home size, duct material, accessibility, and region, with a per-linear-foot breakdown.
Answers: "How much does it cost to replace ductwork?"
Open calculatorAC Installation Cost Calculator
Installed price of a new central AC, heat pump, or mini-split — by size, efficiency, new-vs-replacement scope, ductwork, and region.
Answers: "How much does it cost to install central air?"
Open calculatorFurnace Replacement Cost Calculator
Installed cost of a new gas, electric, oil, or propane furnace — by size, AFUE efficiency, replacement-vs-new-install, and region.
Answers: "How much does it cost to replace a furnace?"
Open calculatorHVAC Estimate Calculator
Contractor job pricing from the bottom up — labor, equipment, materials, overhead, and true profit margin (not markup).
Answers: "What should I quote for this job?"
Open calculatorHydronic Boiler Sizing & EDR Calculator
Net and IBR gross boiler output from connected radiator EDR and supply water temperature — with temperature correction and oversizing risk warnings.
Answers: "What boiler output do I need for my radiators?"
Open calculatorCooling Tower Tonnage Calculator
Condenser water heat rejection capacity (BTU/h and tons), approach to wet-bulb, and chiller reject load — with approach and under-capacity warnings.
Answers: "How many tons can my cooling tower reject?"
Open calculatorMore trades on the way
HVAC is the first set. Calculators for the other trades TradesQuote supports are coming next:
Coming soon
Which calculator do I need?
Match your question to the right tool. For a full cooling install, the natural order is: BTU → Tonnage → CFM — get the load, pick the system size, then set the airflow targets.
| You're asking… | Use this tool | The rule it's built on |
|---|---|---|
| What size AC do I need? | BTU Calculator | ~20 BTU per sq ft, adjusted for climate, sun & insulation |
| How many tons is X BTU? / What tonnage for my house? | Tonnage Calculator | 1 ton = 12,000 BTU/hr |
| Convert tons, BTU/h, °F, or static pressure units? | HVAC Unit Converter | tons × 12,000 = BTU/h · °C = (°F−32)×5/9 · Pa = in.w.c.×249 |
| What size furnace do I need? | Furnace BTU Calculator | 30–60 BTU per sq ft by climate, ÷ AFUE for input size |
| What size heat pump do I need? | Heat Pump Sizing Calculator | Size to cooling tons; check heating load & balance point |
| What size ductless mini-split for this room? | Mini-Split Sizing Calculator | 20–30 BTU/sq ft per zone, rounded to the nearest head |
| How much airflow does this room / system need? | CFM Calculator | volume × ACH ÷ 60 · 400 CFM per ton |
| What size duct does that airflow need? | Duct Size Calculator | smallest diameter whose capacity ≥ CFM (flex −25%) |
| Is my AC temperature split healthy? | Delta T Calculator | cooling split 16–22°F · furnace rise 40–70°F |
| Is my duct system restricting airflow? | Static Pressure Calculator | TESP = supply static + |return static| ≤ nameplate max |
| Is my refrigerant charge correct (suction side)? | Superheat Calculator | superheat = suction line temp − saturation temp |
| Is my refrigerant charge correct (liquid side)? | Subcooling Calculator | subcooling = saturation temp − liquid line temp |
| What superheat should a fixed-orifice system target? | Target Superheat Calculator | ((3 × indoor WB) − 80 − outdoor DB) ÷ 2 |
| How much refrigerant for extra line set length? | Refrigerant Charge Calculator | (total length − factory allowance) × oz/ft by line size |
| What is the dew point / RH for this air sample? | Dew Point Calculator | Magnus approximation from dry-bulb + RH (or inverse) |
| How is coil load split between sensible and latent heat? | Sensible & Latent Heat Calculator | Qs = 1.08×CFM×ΔT · Ql = 0.68×CFM×Δgrains · SHR = Qs/Qt |
| What happens to CFM and static pressure if RPM changes? | Fan Laws Calculator | CFM ∝ RPM · SP ∝ RPM² · BHP ∝ RPM³ |
| How much whole-building ventilation CFM is required? | Ventilation Calculator | 62.2: 0.03×area + 7.5×(beds+1) · 62.1: occ×cfm/person + area×cfm/sqft |
| What size humidifier or dehumidifier do I need? | Humidity Control Calculator | Ql = 0.68×CFM×Δgrains · pints/day = Ql×24÷12,000 |
| Is the higher-efficiency unit worth the price? | SEER Savings Calculator | % saved = 1 − (old SEER ÷ new SEER) |
| Is a higher-efficiency heat pump worth it for heating? | HSPF Savings Calculator | % saved = 1 − (old HSPF ÷ new HSPF) |
| Is a higher-efficiency furnace worth it? | AFUE Savings Calculator | % saved = 1 − (old AFUE ÷ new AFUE) |
| What does it cost to run my system? | Operating Cost Calculator | BTU ÷ efficiency × hours × energy price |
| How much will the replacement cost? | Replacement Cost Calculator | base price × size × efficiency + ducts, × regional labor |
| What should I quote for this job? (contractors) | HVAC Estimate Calculator | (labor + equipment + materials + overhead) ÷ (1 − margin) |
| What is my boiler's combustion efficiency? | Combustion Efficiency Calculator | η = 100% − qA − L_latent − 1.5% radiation (Siegert formula) |
| What is my HRV or ERV's sensible effectiveness? | HRV / ERV Effectiveness Calculator | εs = Vs×(t₁−t₂) / [Vmin×(t₁−t₃)] × 100 (ASHRAE 84) |
| What friction rate should I use for Manual D duct sizing? | Duct Friction Rate Calculator | FR = (ASP × 100) / TEL · target 0.06–0.18 iwc/100' |
| What boiler output does my hydronic radiator system need? | Hydronic Boiler Sizing & EDR Calculator | Q = EDR × 170 × (ΔT/110)^1.3 · gross = net × 1.15 |
| How many tons can my cooling tower reject? | Cooling Tower Tonnage Calculator | Q = 500 × GPM × ΔT · approach = T_cold − WBT ≥ 5°F |
| How many air changes per hour does this space have? | ACH Ventilation Calculator | ACH = (CFM × 60) / volume · check ASHRAE 62.1 / 62.2 / 170 |
| What are all the psychrometric properties of this air sample? | Psychrometric Calculator | W = 621.945×Pv/(Patm−Pv) · h = 0.240×T + (W/7000)×(1061+0.444×T) |
Every HVAC formula on one page
Every rule of thumb behind these tools, on one page. Each calculator's page walks through its formula in plain English with worked examples — this is the cheat sheet.
All of these are planning rules. Final equipment selection should be confirmed with ACCA Manual J (loads) and Manual D (ducts) — every calculator says so, because right-sizing beats guessing in comfort, efficiency, and equipment life.
Frequently asked questions
About the calculators, their accuracy, and what's next.
Are these HVAC calculators really free?
Yes. All thirty-two are completely free, run instantly in your browser, and require no account or sign-up. They're planning and field-check tools built by TradesQuote, the AI estimating platform for trades businesses.
Which HVAC calculator should I use first?
For cooling installs, the natural order is BTU → Tonnage → CFM. For code ventilation, use the Ventilation Calculator after CFM targets. For field diagnostics, start with Delta T, then Static Pressure if the split is high, Superheat or Subcooling if charge is suspect, and the Refrigerant Charge Calculator for long line sets. For moisture and coil load, use Dew Point and Sensible & Latent Heat; for humidifier or dehumidifier sizing, use Humidity Control. For combustion and boiler work, use Combustion Efficiency and Hydronic Boiler EDR. For air quality and ventilation compliance, use the ACH Calculator. For psychrometric analysis, use the Psychrometric Calculator.
Are the results accurate enough to buy equipment?
They give reliable planning estimates using the same rules of thumb contractors start with. Before purchasing or pulling permits, confirm final sizing with a full ACCA Manual J load calculation and Manual D duct design, which account for windows, orientation, infiltration, and duct losses.
What are Manual J and Manual D?
They're the ACCA design standards used across the US industry. Manual J is the room-by-room heating and cooling load calculation; Manual D is the duct design method that turns airflow targets into duct sizes. Permits and equipment warranties typically require them.
Do these calculators work for commercial buildings?
They're tuned for residential and light-commercial spaces. Large commercial buildings have ventilation codes, occupancy loads, and zoning requirements that need engineering-grade load calculations — treat results there as rough first approximations only.
Will calculators for other trades be added?
Yes. HVAC is the first set — calculators for carpentry, painting, cleaning, electrical, and plumbing are planned next, matching the trades TradesQuote supports for AI-powered estimating.
Calculators size the equipment. TradesQuote prices the job.
Once you know the BTUs, tons, and CFM, the real work is the quote. Describe the job or upload photos, and TradesQuote's AI builds a detailed line-item estimate — quantities, unit prices, and totals — validated by a built-in quality control agent and ready for your client to sign online.
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Quantities, unit prices, and totals generated instantly.
Knowledge base
Upload past jobs so estimates reflect your real pricing.
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From the Blog
Guides and deep-dives on HVAC sizing, diagnostics, efficiency, and cost.
HVAC
Commercial HVAC Tons per Square Foot (Sizing Guide)
Commercial HVAC sizing by square feet per ton, with planning figures for offices, retail, restaurants, warehouses, and server rooms — why internal gains dominate and why a block load calc is required.
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Duct Size Chart: How to Match Duct Size to CFM
A round duct size chart by CFM, what a ductulator actually does, the friction-rate and velocity rules behind it, how to convert round to rectangular, and how to size supply vs return ducts.
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Furnace and AC Replacement Cost (Replacing Both Together)
What it costs to replace a furnace and air conditioner together: combined price ranges by efficiency tier, why a matched system is worth it, the cost breakdown, and when to replace just one.
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