Aquatherm Product Description

When a First Co. Aquatherm® "Combo Heater" (air handler) is connected to an adequately sized natural gas, LP, or oil fired water heater, the water heater becomes a dual function appliance that can provide comfortable, efficient space heating as well as hot water for domestic use. 

First installed in California in 1974, there are now over a million Combo systems in operation from Canada to Florida and in both single and multi-family applications.

Contact First Co.  for a list of Aquatherm® installations in your area.






Any water heater sized large enough to accomplish both functions (space and water heating) will special water heater is needed! Water heaters used for space heating will generally require extra gallon capacity and higher BTUH input. (See "Equipment Sizing")


• High Efficiency:

The recovery efficiency of today's natural gas water heaters ranges from 76 to 94%. As a general rule of thumb, the space heating efficiency of any water heater can be approximated by adding several percentage points to the water heater's recovery efficiency. The efficiency gained by these systems comes from the fact that:  

  1. Eliminating the gas furnace saves the energy that would normally be lost due to the furnace vent, gas pilot, and furnace cabinet.

  2. Laboratory and field tests have proven that water heater standby losses are reduced when the water heater is operated more frequently.

• Low Maintenance:

Combo Heaters are simple and uncomplicated compared to heat pumps and high efficiency gas furnaces. The heating system has only five moving parts!

• Compatible Cooling Coils:

Cooling coils installed in First Co. Combo Heaters are completely compatible with major brands of condensing units. Two models ( HBQB and HBXB-HW Series) obtain efficiencies up to 14 SEER, depending on the outdoor unit.

To insure compatibility and to obtain efficiency information, contact your local distributor, or First Co., or click here for our product efficiency ratings page.

• Consistent, Comfortable Heat:

As long as hot water is available, Combo Heaters will provide warm air no matter what the temperature is outside. Homeowners report being much more comfortable with hydronic heat than with other space heating systems, such as heat pumps.

• Longer Water Heater Tank Life:

By circulating water through the water heater more frequently, sediment build-up is reduced, corrosion is minimized, and the life of the water heater tank is extended.

• Flexibility:

The First Co. product line includes a variety of different Aqua Therm® Combo Heaters. Models are available to recess in a wall, install above the ceiling, in a closet, or in an attic. You can choose models for heating only or with cooling coils up to five tons. There's even a heating coil to add to your existing air handling unit.


Technical Considerations

Equipment Sizing

• Air Handler Selection:
Select an air handler with a heating output that exceeds the space heating loss of the structure and that has a cooling coil sized to match the outdoor condensing unit. Special note...the heating output of the air handler or hot water coil will not be greater than the output of the selected hot water heater. Therefore, if the water heater is undersized, the heating BTUH of the air handler will be LESS than it's rated output.

• Water Heater Selection:
The following sizing information should only be used as a basic guide to adequate water heater sizing because of variations in each family's domestic hot water requirements. For additional assistance in water heater sizing contact a qualified professional engineer.

Proper water heater sizing should consider both the gallon capacity AND the BTU input of the water heater.

  1. To determine water heater GALLON CAPACITY:
    A minimum 40 gallon high recovery and/or high efficiency gas or oil-fired water heater is recommended. The following volume sizing guide is satisfactory in most areas of the country:
    • 600-800 CFM air handlers - Minimum 40 gallon water heater
    • 1000-1200 CFM air handlers - Minimum 50 gallon water heater
    • 1400-1600 CFM air handlers - Either two 40 gallon water heaters piped together, one high input 50 gallon (63,000 to 75,000 BTU input), or one 72 to 75 gallon
    • 2000 CFM air handlers -Any combination of water heaters having at least 105,000 BTU OUTPUT.
  1. To determine water heater BTU INPUT:  
    (Assumes a water heater recovery efficiency of 76%). For mild climates...BTU INPUT = structure's heat loss x 1.51. For colder climates...BTU INPUT = structure's heat loss x 1.58.

• Condensing Unit:
Selection of the condensing unit size should be determined by the "Manual J" method or other approved heat loss/heat gain calculation procedure.
Certified cooling capacities and efficiency information are available upon request.

• Air Handlers:

All "Q" type air handlers include a factory installed circulating pump, hot water check valve, and purge valve. R22 and R410A expansion valves are also available.

• Water Piping:

Water piping between the water heater and air handler should be 3/4" (1" on 5 ton models) nominal copper or other code approved material.

When installed in an area subjected to freezing temperatures, the water piping should be completely insulated and a "freeze protector" should be installed on the hot water coil (contact factory).

To prevent air lock of the circulating pump, the piping connections to and from the air handler MUST come from the horizontal connections of the"T" fittings in the vertical hot and cold water supply lines at the water heater (see diagram above).

Maximum distance between the water heater and air handler should not exceed 100 feet (one way).

• Thermostats:

All "Q" type air handlers are compatible with any standard 24 volt thermostat.

Specification Docs:

Installation Docs:

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