A combi boiler is a single, compact unit that provides both space heating for a home and instantaneous hot water for domestic use without requiring a separate water heater or storage tank. Also called combination boilers, these systems use internal heat exchangers to divert boiler output for heating water on demand when hot water fixtures open.
Technical Specifications
Combi boilers range from 24 to 35 kW output with heating capacities from 60,000 to 120,000 BTU per hour. They deliver hot water flow rates of 2 to 5 gallons per minute while maintaining temperature accuracy within 2 degrees Fahrenheit. Operating pressures reach 80 to 100 PSI. Efficiency ratings typically exceed 90 percent AFUE (Annual Fuel Utilization Efficiency). Most models operate on natural gas or propane with electronic ignition systems.
Advantages and Considerations
Combi boilers occupy minimal space compared to traditional boiler-plus-tank systems, making them ideal for compact homes and apartments. They eliminate standby heat losses, reducing energy consumption by 15 to 30 percent. Installation costs range from $2,500 to $4,500. However, they cannot simultaneously provide high-volume space heating and hot water without temperature reduction, making them less suitable for large homes with extensive radiator systems and multiple simultaneous hot water demands.