HVAC
BTU Calculator
BTU needed to heat or cool a room from its size, insulation, windows and occupancy.
BTU/h = volume × base load × sun × insula…
Also called btu calculator for room · air conditioner size
Home & Construction · 8 calculators
HVAC Calculators
Room BTU, AC tonnage, heating and cooling loads, airflow and CFM, duct size, HVAC efficiency and energy cost.
HVAC
AC Tonnage Calculator
Air conditioner tonnage for a room, with the BTU rating and estimated running cost.
1 ton of cooling = 12,000 BTU/h
Also called ac size calculator · how many tons ac
HVAC
Heating Load Calculator
Heating load for a home from floor area, insulation standard and design temperatures.
load = area × specific load × ΔT ÷ design…
Also called boiler size calculator · heat pump sizing
HVAC
CFM Calculator
Airflow in CFM for a room from air changes per hour, and the fan size it implies.
CFM = room volume × ACH × 0.5886
Also called air changes calculator · ventilation cfm
HVAC
Duct Size Calculator
Round or rectangular duct size for a required airflow at a sensible velocity.
A = Q / v
Also called ductwork sizing · air duct diameter
HVAC
Temperature Difference Calculator
Difference between two temperatures in any scale — remember a difference converts differently from a reading.
ΔT(°F) = ΔT(°C) × 1.8
Also called delta t · temperature change between
HVAC
HVAC Efficiency Calculator
Convert between SEER, EER and COP, and compare the running cost of two units.
COP = EER ÷ 3.412
Also called seer to cop · eer calculator
HVAC
Electricity Cost Calculator
What an appliance costs to run per hour, day, month and year at your tariff.
cost = watts ÷ 1000 × hours × rate
Also called appliance running cost · cost to run appliance
Key hvac formulas
| BTU | BTU/h = volume × base load × sun × insulation + occupant and window loads |
|---|---|
| AC Tonnage | 1 ton of cooling = 12,000 BTU/h |
| Heating Load | load = area × specific load × ΔT ÷ design ΔT + hot water |
| CFM | CFM = room volume × ACH × 0.5886 |
| Duct Size | A = Q / v · d = √(4A / π) |
| Temperature Difference | ΔT(°F) = ΔT(°C) × 1.8 |
| HVAC Efficiency | COP = EER ÷ 3.412 · SEER ≈ EER ÷ 0.875 |
| Electricity Cost | cost = watts ÷ 1000 × hours × rate |
HVAC questions
How many BTU per square metre?
Roughly 450–600 BTU/h per m² of floor for cooling in a standard 2.5 m high room, before adjustments.
How much does it cost to run a 2 kW heater for an hour?
At 28p per kWh it costs 56p an hour — 2 kW × 1 hour = 2 kWh.