Comparing Indirect-Fired and Conventional Gas Water Heaters

December 18, 2023

This post is recommended in particular for homeowners who have a hot water gas boiler heating their home, families who may have hot water baseboard heaters, in-floor radiant heating, and/or radiators – all of which are connected to the central boiler in the mechanical room.

Many of us who have a boiler are already aware of the versatility of this type of heating system, including one of those options that often hovers around the outskirts of the conversation: a great product that’s known as an indirect-fired water heater.

We’ve talked about them plenty in past posts, and in this one we’ll take a closer look at how high performance indirect-fired water heaters perform in comparison to conventional gas water heaters, products which sometimes don’t quite measure up to our hopes and expectations.

Steam Shower

Conventional Gas Water Heaters

Bradford White water heater install with expan. tank

Along with its storage tank, a conventional, standard gas water heater has gas burners, an automatic gas control valve, and a flue pipe that exhausts hot gases from the combustion process inside the unit to the outdoors. A conventional water heater is an independent, gas-fired appliance whose sole job is to heat domestic hot water for cooking, showering, and other household tasks.

This type of water heater is often what comes to mind for many homeowners when discussing these products. In some areas of the country, and in certain places around the Denver-Boulder metro area, electric-powered tank type water heaters are also prevalent. Our focus for this discussion, however, will be on gas-fired tanks, which normally provide greater hot water supply than electric water heaters.

The warranties on conventional gas water heaters typically range between 6 and 12 years for the storage tank, depending on the manufacturer and the model.

Indirect-Fired Water Heaters

Also known as an “indirect water heater” or a “sidearm tank,” indirect-fired water heaters do not have a flue pipe and they don’t directly burn gas. Instead, an indirect water heater has a durable, high efficiency, water-to-water heat exchanger built into the unit, which uses hot water from the central hot water boiler to heat domestic water surrounding the heat exchanger inside the tank. The indirect-fired water heater is connected to the central hot water boiler as an independent zone, and is often prioritized in the boiler controls for optimal performance.

SuperStor Ultra - closer look image

High Performance Hot Water Supply

Because of the high BTU rating of the boiler that’s powering the indirect water heater – significantly higher than standard gas water heaters – plus its energy-efficient storage tank with no flue pipe to lose heat thru, indirect-fired water heaters are known to far outperform standard gas water heaters in all important measures. In addition, the central boiler is typically much more efficient than a standard water heater, capable of supplying hot water at a much higher efficiency rating.

Indirect-fired water heaters normally have excellent, long term warranties. In the case of the SuperStor Ultra indirect water heater that our team installs regularly, if registered within the first six months (our team does this for our customers), the warranty on the storage tank is lifetime for the original purchaser.

Comparing Indirect-Fired and Standard Water Heater Performance

For comparison, let’s take a look at the key performance ratings of some common conventional gas water heaters and the SuperStor Ultra indirect water heater, focusing on the First Hour Ratings (FHR), BTU sizes, and recovery rates:

Bradford White Water Heaters
Superstor Ultra water heater logo

Bradford White Conventional Gas Water Heaters

Bradford White has been manufacturing high quality hot water solutions for over 130 years and continues to be based in the U.S. These water heaters feature glass-lined tanks, which normally last anywhere from 8 to 15 years in the Denver-Boulder area. We will focus on two different Bradford White 50 gallon models that are common in our market, a standard model and a high recovery model.

Bradford White Defender hwh (1)

BW Model: RG250T6N (standard gas water heater)

  • BTU gas input rating: 40,000 BTU/hour
  • FHR: 81 gallons
  • Recovery rate at a 90-degree Fahrenheit temperature rise: 43 gallons/hour

BW Model: RG250H6N (high recovery gas water heater)

  • BTU input rating: 65,000 BTU/hour
  • FHR: 106 gallons
  • Recovery rate at a 90-degree F temperature rise: 70 gallons/hour

SuperStor Ultra Indirect-Fired Water Heaters

SuperStor Ultra water heaters are manufactured by Heat Transfer Products (HTP), founded and based in the U.S. for nearly 50 years. These heaters have a highly durable, 316L grade stainless steel storage tank. For this comparison with the Bradford White 50 gallon models listed above, we will focus on the 45 gallon SuperStor Ultra.

Model: SSU-45N

The first-hour hot water rating of the SSU-45 at a 140-degree F tank setting (normal for most homes), with 180-degree F boiler water (also standard), is 212 gallons per hour – twice the FHR as the high recovery Bradford White water heater! When matched with an appropriately sized boiler, over 200 hundred gallons of hot water at your immediate disposal from just a 45 gallon storage system!

HTP Water Heater

Keep in mind that the central boilers that power indirect water heaters are normally sized to heat an entire home, with BTU ratings often in the 100,000 to 200,000 BTUs per hour range. Compared to the significantly lower BTU ratings of virtually all standard water heaters (approx. 40,000 to 65,000 BTU), an indirect water heater connected to a boiler as a prioritized zone provides extremely fast hot water recovery.

Triangle Tube boiler install-from Russ (4)

Due to variables such as the size and efficiency of the central boiler, and the controls arrangement, printed recovery rates for indirect water heaters are less clear-cut than they are for standard water heaters. However, based on the data discussed above, in particular the water heater’s FHR ratings with a connected boiler, hot water delivery from the indirect water heaters our team installs is consistently significantly greater than all standard gas water heater options. We’ve even had customers comment that their new indirect-fired water heater never seems to run out of hot water!

A Win-Win Hot Water Upgrade for Denver-Boulder Homeowners!

Master Plumber Logo - redMore hot water, quicker. Higher efficiency, reduced gas consumption, and lower heat loss from the storage tank. A long term storage tank warranty, too! If your home is heated by a boiler and you use plenty of hot water on a regular basis, when the time is right we recommend taking the time to learn more about the indirect-fired water heater option. It could be just the hot water solution you’re looking for!

In the Boulder-Denver metro area, our expert hot water team at Save Home Heat Company is ready to assist you with ample amounts of information and free, low-pressure installation quotes for hot water products that make the most sense for your specific needs, and are the right fit for your home.

Please contact me to schedule a water heater upgrade quote for my home!