Glossary
BTU (British Thermal Unit)
Definition
A BTU is the standard unit of measurement for heating and cooling capacity. One BTU is the amount of energy needed to raise the temperature of one pound of water by one degree Fahrenheit. HVAC systems are rated in BTUs per hour to indicate how much heating or cooling they can deliver.
Understanding BTU (British Thermal Unit)
Common reference points: a typical home furnace produces 60,000-120,000 BTU/hr, a residential AC unit ranges from 18,000-60,000 BTU/hr (1.5-5 tons), and a single kitchen burner produces about 7,000 BTU/hr. Properly sizing HVAC equipment to a home's BTU needs is critical — oversized units short-cycle (causing humidity problems and premature wear), while undersized units run constantly without reaching comfortable temperatures.
Related Terms
SEER Rating (Seasonal Energy Efficiency Ratio)
A SEER rating measures the cooling efficiency of air conditioners and heat pumps over a typical cooling season. Higher SEER numbers mean greater efficiency: a SEER 16 unit costs roughly 20% less to operate than a SEER 13 unit. Federal minimums are SEER 14-15 depending on region, while premium units reach SEER 25+.
Tonnage (HVAC Capacity)
In HVAC, tonnage refers to the cooling capacity of an air conditioning system. One ton of cooling equals 12,000 BTUs per hour — the amount of energy needed to melt one ton of ice in 24 hours. Residential systems typically range from 1.5 to 5 tons depending on home size, climate, insulation, and window area.
Heat Load Calculation (Manual J)
A heat load calculation (formally called Manual J) is an engineering assessment that determines exactly how much heating and cooling capacity a home needs. It factors in square footage, insulation levels, window area, climate zone, orientation, occupancy, and dozens of other variables to produce a BTU requirement for proper system sizing.
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