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Trusted local news leader for Prescott area communities since 1882
7:37 PM Tue, Oct. 23rd

Need a new water heater? Consider this

Question: Do I need a permit to install a new water heater?

Answer: Yes, because there have been a number of serious accidents associated with water heater installations by homeowners and bogus contractors. The city now requires a permit, so an experienced person can inspect the installation. There are several safety-related issues the inspector will check for. These include a water expansion tank, temperature/pressure relief valve, combustion air for gas appliances, and, if installed in a garage, the proper height above the floor. These rules are important for safety and economics.

Water heating is the third highest household energy cost, representing 14 percent of your total energy use, according to the Department of Energy. Why? Because water is being heated and distributed throughout the home most of the time 24 hours a day and 365 days a year. When selecting a new hot water appliance, considering the cost of operation is important, especially as these units last between 10 and 15 years; and more if you maintain them correctly and use a water softener in hard-water areas such as Prescott.

As with all energy functions, water heating can be achieved through a number of different ways. The most common is a central tank fueled by either natural gas or electricity; however, there are a number of other solutions, including heat pumps, passive and photovoltaic solar, propane and heating oil. There are also tank-less gas and electric units and heat pump HVAC system desuperheaters. Selection depends on what fuel you have available and what other systems you have in your home and can leverage.

If you have more than one fuel type available in your area, it’s a good idea to compare product and fuel costs, especially if you’re building a new home. Even if you’re replacing a water heater, you may find that you’ll save more money in the long run if you use a different fuel or energy source.The two most popular solutions are natural gas and electrical emersion central hot water tanks. However, in most cases, electrical emersion heaters are an expensive operating option, and only used if natural gas is unavailable. New heat pump units are a good substitute for an electric-only solution and compare favorably with natural gas costs.The lowest-priced storage water heater may be the most expensive to operate and maintain over its lifetime. Therefore, before purchasing make sure it’s the correct size. To properly size a storage water heater, use the water heater’s first hour rating (FHR), which is the amount of hot water in gallons the heater can supply per hour. The Federal Trade Commission requires an EnergyGuide Label that lists FHR on all new storage water heaters.

Determine which hour of the day you use the most hot water and calculate your use. For an individual function usage list, go to http://www.ahrinet.org/App_Content/ahri/files/Homeowners/Water%20Heater%20worksheet.pdf. Select a water heater FHR slightly higher than your maximum total one hour use. Now determine the cost to operate that size system for different fuel types.

As an example, using the DOE on-line calculator for water heaters at https://energy.gov/eere/femp/energy-cost-calculator-electric-and-gas-water-heaters-0. The calculator shows that an electric heater would cost $551.00 per year to operate and a natural gas heater would cost $274.00 per year; a $278.00 or 51 percent saving using natural gas.

Of course, these calculations can be achieved manually. The energy required to heat water in BTUs

= (Volume in gallons x Water weight) x Temperature change ΔT

Where the average daily volume in gallons is 64

The weight of water is 8.345 pounds per gallon

The temperature rise from cold to hot is 77°F (50°F to 127°F)

An average natural gas water heater has a 62 percent efficiency factor (EF)

(64 x 8.345) x 77 = 41,124 BTU

Now O/P BTU x EF = I/P BTU

41,124 x 62% = 66,329 BTU

Cost for Gas = #Therms x (cost per Therm)

Therm = 100,000 BTU and costs $1.13

(66,329/100,000) x $1.13 = $ 0.75 per day

Cost per year = $0.75 x 365 = $274 p.a.

Alternative Heat-Pump water heaters. They are twice as efficient as electric water heaters and support operating costs comparable to natural gas units. A heat-pump isn’t making heat as an electric resistance or natural gas unit does its transferring heat from the surrounding air to the water. This is done by circulating a “refrigerant” fluid that can be alternately evaporated into a gas and condensed into a liquid by changing its pressure; its higher efficiency is because it transfers more energy from the air to the water than the electricity used to run it.

A typical heat-pump Efficiency Factor (EF) or Coefficient of Performance (COP) ranges from between 2.0 and 2.5, while the EF of an electric-resistance water heater is always less than 1.0. Now if we assume that the average heat-pump has a 200 percent EF, and uses the equation above the Heat pumps cost per year to operate is $259. This is compared to $552 pa for the electric-resistance unit and $274 pa for the natural gas unit. Based on cost, the heat pump is the most economic to operate, and much less complex to install and maintain than the gas unit.

Unfortunately, heat-pump water heaters can’t heat water as quickly as electric resistance or natural gas units. While the electric-resistance unit can heat 20 gallons per hour, a heat pump can only manage about 8 gallons per hour. To make up for this deficiency, heat-pump water heaters are equipped with an electric resistance element that is energized whenever the heat pump can’t keep up with the demand for hot water. This feature improves performance of the unit but introduces a cost penalty.

A disadvantage of heat-pump water heaters is that they rob heat from the room where they are located. The units are often installed in a basement or garage, but they should not be put in a space that can drop below about 40°F as the EF will drop as the ambient temperature drops, and the cost to operate increases.

Finally, heat-pump water heaters are higher priced. The average cost of a 50-gallon tanked heat pump is between $1,200 and $1,400 as compared to an electric resistance unit of between $300 and $500. However, their operating efficiency provides a payback period of three to for years; and for Energy Star acceptance only heat-pump models make the grade. Heat-pump water heaters are also an ideal solution when using photovoltaic solar panels as they are electricity efficient and use power in off periods.

Other issues you should consider are the initial cost of the unit, and installation costs. It is always necessary to consider health and safety effects when using different fuels. If using natural gas or any other combustible fuel, it is recommended that direct vent units are used to prevent combustion and back draft safety issues. Also, to maximize water efficiency, a timer-and-switch-based recirculation system is recommended as it prevents water loss while waiting for hot water to reach the use point from the tank.

For more information contact Paul Scrivens at www.greenhomeenergyadvisors.com