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Indirect Water Heaters

Kitchen, Bath, Plumbing and Heating Experts

Indirect Water Heaters

Indirect water heaters utilize the output of your boiler to heat your domestic hot water – this is accomplished by piping a zone off the boiler through the indirect heater’s built in heat exchanger.  This exchanger becomes part of the heating system’s “closed loop” and never sees contact with the potable hot water supply. Particularly if the heat source boiler is set to “cold start.”

The primary advantage of indirect heater’s over a regular, vented-type water heater is the much higher output of hot water.  Manufacturers utilize what’s called a “first hour delivery” rating to measure the capability of a water heater.  This rating is derived by taking the existing hot water in the tank, and how much hot water can be generated after depletion, within the first hour.  For example, a regular 40 gallon gas atmospheric vent water heater has 40 gallons of hot water available.  After those 40 gallons are utilized, the water in the tank becomes increasingly colder as the hot water is replenished with cold water.  This cold water will eventually heat up to meet the demand of the water heater’s thermostat setting.  The first hour delivery rating is a function of 1) tank size; 2) BTU/hr of heat input; 3)degree of temperature rise (using a 90 degree temperature rise most accurately reflects performance)  Below, I’ll offer an apples to apples comparison between a Rheem 40 gallon atmospheric vent water heater, which fires at 40,000 BTU/hr versus a Dunkirk 40 gallon indirect, which, depending on the circulator size, will have an input of approximately 80,000 BTU/hr

Rheem 40 gallon gas first hour delivery, at a 90 degree temperature rise – 66 gallons

Dunkirk 40 gallon indirect first hour delivery, at a 90 degree temperature rise – 200 gallons

Central Plumbing and Heating Supply | Types of Indirect Water Heaters

We stock two different series of Dunkirk Indirect water heaters – a stainless steel version and a glass-lined version.  The stainless steel models are composed of a stainless steel tank, smooth stainless steel heating coil, as well as stainless steel dip tube, aquastat well, and domestic water connections.  The glass-lined version uses an enameled steel tank and enameled heat exchanger.

  • H2OI Stainless Steel Single Coil Features
    The stainless steel indirect water heater is the top-of-the-line choice offering longevity and energy efficiency.  Constructed of 316L stainless steel, this tank is backed by a Limited Lifetime Warranty when installed in a residential application.  It also has 2.25” of insulation and will only lose a half-degree per hour of standby.  
    • Limited Lifetime Warranty
    • 1” tappings for boiler inlet/outlet (all models)
    • ¾” tapping  for hot water inlet/outlet (40 and 50 gallon models)
    • 1” supply tapping for hot water inlet/outlet (80 gallon model)
    • Seven sizes available (30, 40, 50, 60, 80, and 115 gallon)
    • High output models available for situations requiring a rapid tank recovery
  • H2O Glass Lined Features
    The glass lined indirect water heater offers an affordable solution in areas where high chloride levels in the domestic water supply can corrode a stainless steel tank. The internal coil delivers unmatched performance with a large surface area resulting in high domestic hot water ratings.
    • Residential Limited Warranty: Tank, 8-Years; Parts, 5-Years
    • 1” tappings for boiler inlet/outlet (all models)
    • ¾” tappings for hot water inlet/outlet (all models)