water heating system

Let’s Talk Boilers: Indirect Water Heating Systems

Why go with indirect heating systems? There’s a variety of reasons why.

There are benefits and drawbacks to the boiler and indirect tank combination system setup. Let’s run through some options so you can make informed decisions about your commercial water heating system.

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As far as commercial water heating is concerned (apartment buildings, restaurants, hotels, etc), 99% of the time you’ll see one of two common setups down in the boiler room. The first is what we call a standard tank-type water heater setup: in this circumstance, you have one large commercial water heater or several smaller water heaters (whether HE water heaters and/or standard water heaters), appropriately sized for that commercial application.

The second typical boiler room setup is a boiler (water or steam) working in tandem with an indirect (or coil) water heater tank. This boiler + indirect tank system is commonly referred to as a combination system. In a combination system, that commercial boiler is providing heating for the air in the building, while also providing the building’s faucets and fixtures with hot water.

(Wondering why a tankless water heater setup isn’t on the list? Because tankless units are typically NOT a good choice for a commercial water heater setup. See for yourself.)

Boiler Basics: Water Heating
We’ve talked a lot about the standard tank-type water heater setup; let’s learn more about the combination system with the indirect tank. With a combination system, you have two main components: 1.) a commercial boiler (could be anything from monster-sized, to something smaller – depending on your application) and 2.) an indirect tank. An indirect tank is the exact same thing as a typical standard water heater, except without the mechanical guts required to heat the water on its own.

Here’s how it works…

Your boiler is already busy running to keep your building warm, especially in the winter.

Image courtesy of energy.gov

Next to the boiler is your indirect tank, full of water. (Remember: boiler + indirect tank = combination system.) There’s a closed loop water line pipe that runs between the boiler and the indirect tank. When that pipe gets inside the indirect tank, it’s twisted around like a corkscrew (or coil) inside the tank, and then it comes back out.

So (very) hot water from the boiler travels through that coiled pipe from the boiler where it was heated, through the pipe in the indirect tank, and back out to the boiler. The heat is transferred from that boiler-heated water in that coil to the cooler water in the indirect tank. As this process continues, all that water inside the indirect tank is heated up to HOT – and that’s the hot water that’s going to come out through your sinks and dishwashers and faucets.

Boiler System Benefits
If you’ve already got a giant boiler working away in your basement (this is typically the case in an older apartment building, for example), then adding an indirect water heater to establish a combination system is one viable option to consider.

Number one, if you already have a boiler, then an indirect tank is a fairly inexpensive addition, and they last fairly long. (Plus, boilers are designed for long-term operation – so you’re already getting a lot of life out of that piece of equipment.) Number two, indirect tanks tend to last longer than a standard tank-type gas-fired water heater.

Here’s why…

A standard atmospheric tank-type water heater pulls in air from the environment, heats that air with a flame at the bottom of the tank, then sends that hot air up through multiple exhaust flues inside the water heater. Baffles in those flue pipes slow the hot air down as it travels upward, heating the water surrounding those pipes as it continues upward towards a collection hood and out the top flue through the chimney and outside. This process causes that standard tank to constantly expand and contract, causing stress on the welded joints. Eventually those high heat exchanges degredate the water heater tank and those welded seams bust open – and that’s when replacement is required.

But with an indirect tank, the temperature differential, or Δ (delta) T, is a lot less. That pipe of hot boiler water (in the coil) is quickly heating the water in the indirect tank, whereas the water in the standard tank-type water heater takes longer to heat up and is exposed to higher heat extremes. So with that coiled pipe inside an indirect tank, you don’t get that constant thermal expansion, so there’s a lot less stress on the tank. Less stress on the tank means less frequent replacement – and that’s less money out of your pocket.

Combination Systems: Points to Consider
Whichever water heating system you choose, there will always be different costs to consider. When you go with a combination system, even if that boiler is already installed in your building, you’ll still end up paying for the extra piping and pumps (plus the electricity to run those pumps), in addition to the indirect tank itself. However, once you make that initial investment, then that combination system should last fairly long.

Also, much like when you choose one big water heater over several smaller units, when you’re down, you’re DOWN. If your boiler goes down, you’re losing heat and hot water, all in one shot: there’s no redundancy and no back up.

And what about all that extra heat in the summer? Sure, in the winter your boiler is firing up, keeping your people and your water warm. But in the summer? You’re still firing up that huge boiler just to heat your water, which is likely wasting you energy – and dollars.

There are a variety of reasons owners of commercial applications (such as restaurants, hotels, and apartment buildings) decide to go with a combination system over a standard tank-type water heating system – or vice versa, regardless of whether or not there’s already a boiler in place. Only a professional, trained water heating system technician can help you determine which set up best fits your commercial application.

Don’t know where to start? Contact our trained professionals at Reliable Water Services (800-356-1444). We’re happy to help you chose the best water heating system for your commercial application.