Gas water heaters
The least expensive and most common type of gas water heater is a storage water heater with a flue up the center of the tank. The flue pipe is usually attached to a draft hood that looks like an upside-down funnel with open slots on the side.
These appliances, technically known as atmospherically vented water heaters, have several advantages over other types of water heaters: They are readily available, they are inexpensive ($400 to $630), and the fuel (natural gas) is cheap.
However, atmospherically vented water heaters also have a major disadvantage: They are susceptible to backdrafting (also known as spillage). When an atmospherically vented water heater is installed in a tight, energy-efficient house, the operation of an exhaust fan anywhere in the house—for example, a kitchen range hood—can suck combustion by-products down the water-heater flue and into the house. Because flue gases sometimes contain carbon monoxide, backdrafting is potentially dangerous. Atmospherically vented water heaters should be avoided unless you live in a mild climate and can place the water heater in your garage.
If you are wary of the backdrafting risk posed by a conventional gas water heater but are still attracted to the simplicity of a tank-style gas water heater without power venting, a good solution might be a direct-vent, sealed-combustion gas water heater from GSW Water Heating of Fergus, Ont. The efficiency of a GSW water heater is no better than that of similar conventional gas water heaters, but a GSW unit offers protection from backdrafting risks. According to the manufacturer, the appliance complies with Canada’s R-2000 technical-performance standard for home construction.
If you want to install a gas water heater inside your home, a safer type of storage water heater is one that is power-vented or equipped with a sealed-combustion burner. Unfortunately, these types of water heaters generally cost about $900 to $1200—significantly more than an atmospherically vented water heater.
The most efficient gas water heaters are called condensing units. The high efficiency of these appliances stems from the deliberate condensation of moisture in the flue gases—a step that wrings a few more percentage points of efficiency out of the combustion process.
Condensing gas water heaters are frightfully expensive. Expect to pay $4000 to $8000 for a unit with a stainless-steel tank, or $2500 for a unit (the Vertex, manufactured by A.O. Smith) with an enameled-steel tank. Paying that much only makes sense if you plan to use your water heater to supply space heat as well as domestic hot water.
Tankless water heaters are getting a lot of attention these days, for at least three good reasons: They are compact, they are highly efficient, and they can provide endless hot water.
The problem with tankless water heaters is the same problem suffered by solar hot-water systems: They usually don’t save enough energy to justify their high purchase price. The cost to install a tankless water heater varies; it can be as low as $1600 or as high as $3000. One reason for the high cost of installation is that these appliances require a nearby electrical receptacle and usually require a new flue. In some cases, the diameter of the gas supply line must be upgraded.
According to a study by Minnesota researchers, tankless gas water heaters use an average of 37% less energy than tank-type gas heaters. The savings range from $42 per year for families that use small volumes of hot water to $121 per year for high-use families. Although these savings are significant, the researchers concluded that they aren’t high enough to justify the high purchase and installation costs of these appliances.