Savings with an Indirect Water Heater

MacPHJr

How can a determine the potential savings of an indirect water heater compared to a standard tank type water heater of the same size

Unknown

standard tank type water heater

A common question,,, one has to look at the "standard type tanks" efficiency,, usually about 60%,, that means 60% of the heat from gas burned is transfered into the water,,,, about 40% of that heat is wasted up the chimney.

Indirects, attached to a low-water content boiler, typically attain their heat source from water heated within a 84-95% unit .

The storage tanks themselves(electric or whatever), are all well insulated, so stand-by losses are minimal,, but what will heat that water-up faster?,, I would opt for the higher efficiency unit supplying gas through water for myself.



The choice is always up to you.

Steamhead

The indirect and boiler

have more heat-transfer surface than a standard gas-fired tank. This not only increases heat-transfer efficiency but also the first-hour rating. Plus there is no flue going up thru an indirect like there is in the gas-fired tank, which eliminates a lot of off-cycle loss. I'd go with the indirect.

SpeyFitter

A few things to consider

A few things to consider:



What heat source are you using to heat them with? If it's a conventional boiler you could see 75-82% efficiency (not including piping losses), if it's a condensing boiler, due to the higher temps that often put a condensing boiler in the non-condensing zone (I try and set the boiler supply to an indirect on a condensing unit in the 160 degree range in most cases - typically about 30 degrees more than the tank temperature), you'll probably see 85-88%, 90% at best, again not including piping losses.

As pointed out above, typical indirects have much higher outputs due to their coils surface area which may allow you to get by with a smaller tank and rely on the recovery of a domestic priority controlled boiler over capacity.

Most indirects people put in are stainless steel for much longer service lifes, typically 15-20 years or more depending on local water chemistry, build quality, type of stainless alloy used, how hard it is used, temperature setting for both domestic tank and coil, and other factors.  Your conventional tank will typically see in the 6-10 year range, 2-5 in commercial or high usage settings.

Also factor in savings for permits and additional venting you would see in not needing to isntall an additional flue for a conventional tank, however you must also factor in additional piping and controls for an indirect tank (so they may balance each other out that way).

As far as total life cycle cost, I think a S/S Indirect is hard to beat.