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What size indirect water heater do you need?
E-mail: geno03245w@gmail.com

If you have a boiler and indirect heater in place now, and it needs replacement
or you want to add indirect to your boiler,
then this page has a run down of information
Your home must have a gas fired boiler to heat water inside the indirect heater
The indirect heater has no way to heat water on it's own.

If your home has hot water baseboard heat or has steam radiators, then you have a boiler, and a plumber would be required to see if boiler can support the indirect heater.

If your home does not have a boiler, then your home usually has gas or electic available for heating water.

If your home has gas furnace, then Family of 5 people can squeeze by with ordinary 50 gallon gas water heater.
Typical shower uses 9 gal hot, and bath uses 20 gallon hot.
50 gallon gas heater with 40,000 BTU burner can deliver 70 gallon first hour (the amount of usable hot water from a single continuous draw).
50 gallon gas heater with 50,000 BTU burner can deliver 85 gallon first hour.
Link: Reliance water heater catelog page 13
Link: Which-is-best gas water heater

If you have gas and need more hot water than 50 gallon heater can deliver, then there are 3 options.
1) Two gas water heaters .... Link: Two-water-heaters
2) A condensing heater. .... Link: Review-Polaris-water-heater
3) A 75+ gallon commercial heater .... Link: Commercial-grade-residential-74-98-gallon-spec-sheet.pdf

If your home is all electric, then there are two options for Family of 5 people
1) Two electric heaters: .... Link: Two-water-heaters
2) 80 gallon heat pump: .... Link: Which-is-best-hybird-heat-pump-water-heater
80-100 gallon commercial heater Link: Reliance water heater catelog page 21

Indirect water heater using a boiler is covered on this page.
This type indirect receives hot water from boiler, and can generally deliver a large and predictable amount of hot water based on size of tank, thermostat setting etc.
There are variety of indirect heater sizes, from 30 gallon up.
Indirect heaters used with solar collector, wood burning stove etc are not covered.
Buy:
Indirect water heaters
Burnham indirect heaters/ from Allied
Powerstor Indirect heaters/ from Bradford White
HTP indirect heaters
Triangle tube indirect heater
Burnham Hydrastone-Lined Indirect-Fired Water Heater, 35 gal
Burnham Hydrastone-Lined Indirect-Fired Water Heater, 50 gal

Typical boiler-indirect manual:
Indirect service manual
Boiler instruction manual
Boiler installation / service manual
Commercial boiler install/ service
Indirect-water-heater-technical-information.pdf
hydrostone-indirect-water-heater-installation-and-service-manual.pdf
Greenstar-12-24i-Installation-Service.pdf

Resources:
add-fan-to-boiler.html
What is an indirect heater?
Indirect heater receives hot water from another source, such as solar hot water system, wood-burning stove, or a boiler, shown Fig 1.
This page applies to indirect heater and boiler systems

Using a water pump activated by thermostat, the hot water from boiler, is circulated through the indirect heater inside a coiled tube or heat exchanger, usually made from metal alloy. The heat exchanger heats potable (drinkable) water inside the direct heater.

INdirect heater does not have it's own heating source, unless specified.
For example, indirect heaters used for solar water heaters, typically have electric heating element for backup.

Indirect heaters have separate inlet-outlet for incoming hot water from boiler or solar panels, and these connections let hot water circulate through the heat exchanger. The heat exchanger is a single-wall or double-wall tube that is sealed and will not allow water from boiler or glycol used for solar panels to mix with the potable (drinking) water.

Indirect heaters have separate set of inlet-outlets for potable water used for household taps, tubs, showers, laundry etc.
First hour delivery from Indirect Heater
Fig 2 shows typical first hour delivery for indirect heater with boiler.
First hour delivery is the amount of usable hot water from a single continuous draw.
-For example a 30 gallon size indirect heater would be able to supply 199 gallons hot water ... assuming incoming cold water from city or water well is 58°F, and thermostat is set at 135°F, which is 77°F higher than incoming water temperature. The heater must be able to raise water temperature 77°F.
-If thermostat setting or incoming water temperatures are higher or lower, then the first hour delivery would be different.
-30 gallon size would have less standby cost than larger heater because there is less surface area to lose heat.

What is first hour delivery
-First hour delivery is the amount of hot water that can be consumed at one time by a family before the water turns too cool to shower. It does not mean hot water will last 1 hour.
What size indirect heater is needed
Fig 3 is the 'recommended' first hour rating that is needed per person in home

A 30 gallon indirect heater would be enough hot water for 12-14 people because a boiler consumes so many BTUs and heats to such high temperatures, that it can easily keep up with demand as it occurs.

Boiler and indirect heater are truly 'unlimited' hot water.
Honeywell L4006 water heater controller
Honeywell immersion thermostat

12-277 volt AC SPST controller
12-48 volt DC
Add to any hot water tank
Surface mount or immersion into tank
Temperature range: 100-180°F
Water over 135° poses extreme danger of scalding.
Add mixing valve.

Buy
Honeywell/ Rheem SP11798B
Honeywell L4006
Line Voltage Mechanical Thermostats

Resources:
Add another thermostat to gas or electric water heater
Advantages-disadvantages mixing valve
Control recirculation pump using controller
L4006 manual
L4006 wiring illustration
Honeywell L8104 water heater controller
Indirect solar glycol system/ not covered by this page
Image shows indirect heater supplied with AO Smith solar glycol heating systems.
Tanks are sold separately, but there is no standard water heater formula to recommend which size is best, and most are 80-100 gallon. You buy what you think will work, or what AO Smith representative recommends for local region.

With solar glycol systems, the indirect heater comes with back up heating element because there is no predictable measure when or how much hot will be available.
Wood heating systems are likewise not covered on this page because there is no measure that can predict which size tank is needed other than individual experience, trial-error, local or manufacturer recommendation.

Solar water systems (not glycol) and wood burning systems are not confined to indirect tanks. They can use ordinary storage tank without heat exchanger coil, or back up element, with the caveat that residential tanks are not rated for temperatures above 150°F, while solar heated water can reach 180°F.
Storage tanks used for non-indirect type installation can include a commercial water heating tank, commercial water heater storage tank, and most frequently the Marathon brand polybutylene tank, popular for high heat rating and large gallonage.
Support the economy:
Buy water heaters from my associate links:

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Troubleshoot electric water heater
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Icon gas valve

How to replace water heater element Waste King disposal
How to wire tankless electric

How to install tankless recirculation


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