By Steve Maxwell
Hot water heating systems are traditionally fired by some kind of boiler, and there are plenty of HVAC contractors who’ll tell you that tank-style heaters won’t work for heating. This is not true, proven by the fact that some tank-style heaters are specifically made for infloor or radiator-style heating systems. Even tank-style water heaters that aren’t specifically made for this can work just fine for many years. The most expensive tank-style heaters are less costly than boilers or combo water heater/boiler units, and tank-style heaters offer four unique advantages.
Maintenance of a tank-style heater is easy enough that most homeowners can do it for themselves. Simply connect a hose to the outlet at the bottom of the tank, then flip a valve to flush the sediment out of the tank once a year. No need for a circulator pump and a service call.
Ideal Water Temperature
Boilers are often designed to put out 180ºF water, but that’s way too hot for infloor heating and leads to less-than-safe radiator temperatures unless you also install a mixing valve to cut back on output water temperatures. But why overheat water and incur unnecessary energy losses only to make that water cooler before using it? Tank style water heaters, by contrast, are quite happy taking in water of any temperature and putting out 120ºF to 140ºF without the need for a mixing valve. This temperature range is perfect for hydronic space heating.
A tank style water heater can act as a space heater during winter, while also providing domestic hot water year-round without any added equipment. Some combo boilers can do this too, but not as simply, as inexpensively or as low maintenance as a tank-style heater.
Compatibility With Alternative Energy Sources
Tank-style water heaters are automatically and easily compatible with alternative energy technologies such as solar collectors or an outdoor wood boiler. Whatever alternative energy source your client has (or plans to have) it can preheat water before entering the tank, saving natural gas or propane as it does. You can’t do this with most boilers.
As you plan an installation and discuss it with your clients, keep these tips in mind:
Tip#1: Install circulation pumps at the lowest part of the system. This minimizes the chance that trapped air will stop pumping action.
Tip#2: Install circulation pumps so the motor is oriented horizontally. Circ pumps are meant to run this way and will last longer than if the motor is installed vertically.
Tip#3: Install flush valves if you’re using a separate heat exchanger. The question isn’t “if” an exchanger like this will need descaling, but “when”. Even though most of the crud builds up on the domestic side of the exchanger, put flush valves on the heating side of the exchanger too, just in case it needs flushing someday.
Tip#4: Choose “smart” circulator pumps. These automatically control the current draw and water flow and use about 75% less energy than standard circ pumps. Smart pumps also include an LED control screen so you can monitor the flow rate and current draw.
Regardless of your situation and plans, you need to begin by choosing a water heater that’s large enough to handle the maximum load of both space heating and domestic hot water. Today’s modulating heaters make this decision less critical than it used to be.
Modulation is a heater’s ability to automatically dial in more or less heat output depending on the load demanded. This means your client gets just as much efficiency if they need just a little heat or all that the heater can put out. Operating the heater at lower firing rates also means less thermal stress on the tank and increases the life of the water heater. Old-style non-modulating heaters, by contrast, operate either full blast or not at all, wasting energy when little heat is demanded. Modulating heaters in the 100,000 btu/hr to 150,000 btu/hr range is ideal for whole-house space heating plus domestic hot water production in most Canadian situations. The best boast verified efficiencies of more than 90%.
Simpler is better, and getting multiple uses from a single appliance is always a good thing. These are the advantages of a tank-style water heater as part of a space heating installation. Just don’t let anyone tell you water heaters aren’t up to the job.