Replacing Your Hot Water Heater?

According to Department of Energy data, heating hot water accounts for approximately 20% of each home’s total energy usage.  Let’s take a look at a few options if you need to replace your existing hot water tank.

A conventional water heater typically uses natural gas or propane to heat a tank of water that’s anywhere from 40 to 80 gallons in size. The drawback of this design is that the water heater is constantly keeping that water hot (so its ready when you need it).  In addition, once the tank has been depleted, there’s no hot water until the water in the tank is re-heated.  So the 3rd shower of the morning might be a cold one.

Today you have a few choices:

Tankless Hot Water Heater:  A tankless heater can be electric or gas but only gas heaters have the capacity to serve an entire house.  With this type of hot water heating, you only heat water when you need it — saving the cost of storing and heating hot water when not in use.  The estimate of cost savings vary widely depending on the efficiency of your existing hot water heater and whether it’s insulated.  If you have an efficient, insulated tank, the savings might be as little as $100/ year making a long payback period.  Consumer Reports looked at the issue and concluded that the energy savings doesn’t pay for the increased cost over the life of the system.  Some families find that costs actually go up because they take longer showers.

There are other problems with Tankless heaters.  First, it’s not “instant hot” – hot water won’t get to your faucet any faster unless the distance to the faucet is lessened.  will still take .  Second, you can’t trickle hot water – Tankless heaters require a minimum flow rate to provide hot water.  Third, they heat the water up by a number of degrees – the colder the water going into the tankless heater; the colder is the water coming out.  So you if you live in an area with big differences in seasons, you might be frustrated with a sense that the hot water is erratic.

Tankless heaters, though, can be a great back-up for a house that usually has only 2 occupants but might have 6 or more occupants for summer months.

Tankless with Small Tank:  Many of the problems with a tankless system can be solved by adding a small tank (maybe 8-10 gallons) on the output end of your tankless system.  Make sure the tank is very efficient and well insulated and many of the problems of the Tankless system can be eliminated.  This does not change the payback period.

Hybrid Tank:  Many companies that make Hot Water Heaters now offer what’s known as a Hybrid Hot Water Heater.  They’re essentially standard electric water heaters but with a small heat pump unit on top that utilizes room air to heat the water as much as possible. They do have elements to cover high-demand periods, but offer a number of settings to meet demand and/or minimize energy consumption.  Most of what I’ve read suggest that the monthly savings is much greater than with a Tankless system.  They fit into the same space and with the same connections as a standard hot water heater making installation relatively easy with most homes.   For an all electric house, this choice seems to be a good one.

Solar Hot Water Heater:  Hawaii has become the first state to require solar water heaters in new homes. Other areas with high number of sun-days like Arizona and Florida also have a high proportion of solar hot water heaters.

solar hot water collector next to photovoltaic array
solar hot water collector next to photovoltaic array

Solar hot water systems have two parts:  a rooftop collectors (shown above) and a storage tank with built in heat exchanger. The solar collector is usually made up of copper tubes and a copper plate that is covered with a highly selective absorber coating; this assembly is enclosed in a well-insulated aluminum frame and covered with low-iron tempered glass glazing. A propylene glycol solution within the copper tubes is heated in the collectors and circulated through a heat exchanger located in the bottom of the solar storage tank. The household water contained within the storage tank is heated by the solution circulated through the heat exchanger. The propylene glycol solution is gradually heated by the sun’s energy which is transferred to the solution in the collectors. Reliable automatic controls operate a circulation pump and provide optimal solar water heater system operation.

The solar collectors have to be installed on a roof with at least at 15% pitch.  The ideal orientation for the solar collectors is due south. The collectors can be rotated from south, up to 45° east or west with minimal loss in solar heat gain.  Solar water heaters are always installed with an auxiliary heat source, or in addition to your regular electric or gas water heater. That means that even on cloudy days they will still have hot water. To maximize their savings, homeowners should attempt to use the most hot water in the late morning and early afternoon when the solar system is operating at its peak.

Payback for a solar hot water heater may be up to 10 years without any tax incentives.
Instant Hot Water:  While you’re talking with your plumber about replacing your hot water heater, also talk with him about what system is right for your home to provide faster hot water at the faucet.  In many homes, you have to run the water for 30 seconds before you get water hot enough to take a shower or wash your hands.  You can install systems either a loop in your plumbing system that circulates hot water back to the hot water heater.  If this isn’t possible, another alternative is a recirculating pump.  These products employ a temperature actuated by-pass valve that connects the cold and hot water supply lines at the fixture that is farthest away from the water heater. The bypass valve uses the cold water line as the return loop back to the water heater.  This change can save lots of water that would otherwise go down the drain while you wait for hot water.
First Things First
And of course just like other energy savings measures, you can save lots of water and energy by taking simple steps before you place your hot water heater:
– Turn the thermostat down. Many water heaters are set to between 140 and 180°F (60 and 82°C). See how low you can go. Try 125°F (52°C) for starters. A hot tub is 106°F (41°C). How much hotter do you need?
– Wrap the water heater with insulation. Insulated water heater “blankets” are usually available where water heaters are sold. (Be careful with natural gas or propane fired water tanks. They use an open flame to heat the water. You need to provide a space for air at the bottom of the tank, and at the top where the flue exits the tank. Safety comes before efficiency!)
– Fix those drips. They may not look like much, but they are a constant and persistent drain on your water heating load, and they waste water too.
– Use flow restrictors and faucet aerators to reduce your hot water consumption.
– Find other ways to use less hot water. Wash only full loads of clothes and dishes.
– Insulate your hot water pipes.

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