Important to consider the performance, operating costs and the impact on the environment of the water heater you choose when you replace your aging water heater before it leaks or deciding on a water heater for your new home.
Types of water heaters
Natural gas water heaters
Atmospheric (gravity) vent storage tank
The exhaust chimney is installed to a draft hood that sits slightly above the tank. These water heaters use "gravity" (rising warm air) to exhaust combustion byproducts and are vented through the roof. The exhaust vent is often connected to the furnace vent and they share the same chimney.
Power-vent storage tank
Because of the power-assisted exhaust, it can be placed up to 40 feet from where it is vented through a sidewall or the roof, making it easy to place in a convenient location.
Direct-vent storage tank
These water heaters operate independently of all other exhaust systems in the house. A direct-vent water heater usually must be placed near the outside wall for its exhaust termination.
Power direct-vent storage tank
Because it is power-vented, it can be placed in the most convenient location for the home. Because it is direct-vent, it uses no household air at all - it features a sealed combustion chamber with all the supply air coming from the outside.
Indirect storage tank
The boiler provides the heat for the water and the flue for the exhaust; it treats the tank as simply another heating zone. This system can be extremely efficient, and they typically offer a faster recovery rate than any stand-alone water heater.
Natural gas tankless
They also relatively small and can be hung from a wall or installed in a wall cavity. Tankless water heaters are rated and priced based on how many gallons per minute of hot water they can supply. The net installed cost can be significantly more than the cost of one of the above described water heaters. While they will save the typical homeowner money on the operating costs, the savings alone are generally not significant enough to warrant their installation. Several studies have shown the savings payback on this type of tank is in the 20 to 25 year range. In a retro-fit situation, it is important to ensure that your home has adequate gas pressure and internal piping to handle the increased peak gas demand on the home's system.
Considering installing a tankless water heater? To learn more, view our tankless water heater fact sheet. Contact CenterPoint Energy prior to installing a tankless water heater to ensure that your home has appropriate gas service. Send us an email or call 612-321-5123 or 800-342-4166 for assistance.
With more than twice the carbon footprint of a natural gas unit, substantially more SO2, NOx and mercury emissions, an electric water heater has a greater impact on the environment than a natural gas water heater.
Electric storage tank
To offset this performance shortfall to some extent, plumbers often recommend installing a tank that is double the size of a natural gas unit (For example, 80 gallon electric tank to do the work of a 40 gallon gas model). While the first cost may be lower, the operating cost of an electric water heater is significantly higher. Even with an off-peak pricing package, an electric water heater generally costs more to operate than a gas model, and its recovery cycle will be according to the terms of the off-peak program. Click here to learn more.
Hybrid electric storage tank
These are designed for warm-weather climates where the water heater is typically in the garage. In Minnesota, with the water heater being inside the home, this system is essentially using the home's warmed air to supplement an electric water heater.
Generally speaking, because it is heating with electricity, it will be more expensive to operate and harder on the environment than a natural gas water heater. There have also been significant issues with the performance, not delivering adequate hot water volume (typically can only accommodate one user at a time) and maintenance issues. Tankless water heaters are often referred to as "instantaneous", they do require a constant flow and it will take some time to bring the water up to a desired temperature. While this may be an appropriate application for a vacation home that does not have access to natural gas or propane, it is not recommended for a home or business that has access to natural gas.
The installed cost of a solar water system is significantly higher than that of conventional water heaters, with payback on the system usually exceeding 25 years compared to a natural gas water heater. A solar water heater typically includes collectors mounted on the roof or in a clear area of the yard, with a separate storage tank and a conventional water heater in the home, plus a system controller. There are many types of solar water heater systems, but for the Minnesota climate they must have protection against winter freezing.
Beware of the "orphaned" water heater
High-efficiency boilers and furnaces are direct-vented by way of PVC pipe, typically through the wall. A potentially dangerous situation is created when a water heater is "orphaned" meaning the home's water heater is not upgraded at the same time as the furnace or boiler, leaving the water heater to be the sole user of the metal B-vent.
Originally, the B-vent was sized to accommodate both the furnace/boiler and the water heater. Now, with only the water heater using the venting, the B-vent flue is oversized and may not get hot enough in extremely cold weather to adequately exhaust the water heater's combustion products, resulting in spillage back into the home. This can create a carbon monoxide hazard.
The good way to avoid potential problems with an orphaned water heater is to upgrade your domestic water heater to a power or direct-vent model at the same time when replacing the boiler or furnace. Not only does this eliminate the orphaned water heater problem, but it provides an energy efficiency improvement opportunity as well. When replacing a boiler, the most energy-efficient water heating option is an indirect tank and coil, also called a "sidearm". Whether you are replacing the boiler or the furnace, there are many high-efficiency water heater options for your home. If you decide to retain the existing water heater, the chimney flue may need to be outfitted with a smaller-diameter liner. A "worst case" spillage test should be done on the existing water heater to determine if it can safely be vented via the existing chimney. To learn more about orphaned waterheaters, view the Minnesota Department of Commerce, Division of Energy Resources fact sheet.
Performance / recovery rate
An electric model will typically recover at a rate of 21 gallons per hour - an 80 gallon tank will recover in about four hours, a 105 gallon tank in five hours. Because of this advantage in recovery rates, your family can enjoy one shower after another without a long waiting period.
This is an annual savings of about $200 per year, or about $2,000 over the life of the average water heater. Or taking it one month at a time, and combining purchase price and operating expenses of the water heater, a natural gas water heater will save you about $15 per month.