How Can On demand Coil and Indirect Hot Water Heaters Work?

Tankless coil and indirect water heaters use the space heating system in a particular home to heat the water. When you heat water this way, it's called a "combination water and space heating system," or "integrated heating system."

They work like this: A tankless coil water heater has a heat exchanger or heating coil installed in a home's boiler or main furnace. If a hot water faucet is turned on (such as if you take a shower), the water goes through a heat exchanger as it does so, meaning that this type of tankless water heater provides "on-demand" hot water without using a tank; this is something like an "on-demand" heater, but the boiler or furnace in a home heats the water directly, which means that the tankless coil water heater works best during the cold months when a home's heating system is on all or most of the time. And because of this, this particular type of system is not a good choice, in general, for homes in warmer climates.

That said, though, for most homes, indirect water heaters are very efficient choices overall. They do require a storage tank, unlike conventional tankless water heaters, but because an indirect heater uses the boiler or main furnace to heat the fluid circulated through a heat exchanger in the storage tank, the energy that's actually "stored" by the tank lets the furnace turn off and on less frequently. This in turn saves energy. So if the tank you use is well insulated and the boiler you use is highly efficient, this can be the least expensive way to provide hot water for a home's occupants.

How do the systems run?

As with conventional and ordinary tankless water heater systems, you can actually run the systems in a variety of ways, including powering them with electric, propane, oil, gas, solar energy, or a number of these. Typically, tankless systems run on either electric or gas. Integrated or combination water heating systems can also work with forced air systems, radiant floor heating systems, or hydronic systems.

Which is best for you?

The initial cost of a combination or integrated water and space heating system is going to cost you more than if you install a separate heater and furnace or boiler, but both installation and maintenance costs are probably going to be less. That's because you won't need multiple utility hookups, with just one source of heat, and there's less to maintain, because you have fewer moving parts. Your utility costs may also be lower.

In most cases, people who get combination space and water heating systems are doing new construction, but you can also retrofit these units with existing sources for heating water. Considerations with this type of installation include the size of the system, since the combination system is going to be calculated for size differently than if you're installing separate space and water heating systems. Contact a professional contractor versed in this type of installation for help on what you need for your particular situation if this is something you're interested in doing.

Good models currently on the market for these types of combination systems include BOILERMATE Indirect-Fired Water Heaters, the SuperStor Ultra Stainless Steel Indirect Fired Water Heater, and, especially for those interested in integrating solar energy as part of their systems, Rheem Solar Indirect Water Heater with Back-up Heating Element.