Components of the Gas Hot Water Heater

The standard "tank type" water heater is found in most homes and with just a little maintenance, provides years of trouble free operation. Unlike tankless water heaters which have no storage stank, the tank type water heater heats cold water and stores the hot water until it is needed.

The gas water heater works by a law of physics called convection which loosely paraphrased, states that heat rises. Now please don't run off just because I said "physics". Heat rising and convection is a simple rule that you live with everyday and a hot water tank is no exception. Cold water is supplied to the tank and injected at the bottom of the tank through a dip tube. The denser cold water stays there and is heated by the gas burner. As the water heats up, it naturally rises (physics again...) and is drawn off by the hot water discharge pipe.

The Tankless Water Heater

So you're tired of running out of hot water in the shower and want to replace that old hot water heater. Or maybe you're considering tankless for a new project. Well, tankless water heaters can be a great solution to your residential hot water needs. They're also referred to as on demand water heaters because they don't usually store hot water, but rather create it on demand.

But for all the hype surrounding these appliances there are some limitations and trade-offs to consider before you can really decide if the tankless hot water heater is for you.  Properly used these appliances are absolutely great. Improperly used they are disappointing and expensive. They come in point-of-use and whole-house versions and there are electric tankless water heaters and natural gas or propane models. Some tankless units are sized to heat a cup of tea, others to provide enough hot water for 2 or more bathrooms. Also, the region of the country you live in has a lot to do with how much hot water a tankless water heater can produce.

How it Works

The tankless water heater works by directly heating water on demand, as it is required. Unlike traditional hot water heaters using a storage tank, the tankless units have no storage tank and thereby have no standby heat loss. Standby heat loss is the heat lost and energy wasted by heating water only to store it in a tank and is characteristic of traditional hot water heaters. Avoiding standby heat loss is primarily how tankless water heaters make their claim of being energy efficient.

Whether a tankless water heater is point-of-use like the illustration above or a whole-house unit, they work the same basic way. Cold water enters the unit and is heated by a heating element (heat exchanger) which is turned on by a flow activated switch. The heat exchanger can be electric resistance heating coils or a gas fired burner using natural gas or propane. (Gas units generally have more heating capacity and larger whole-house units are typically gas fired.)

Now here's the rub. There are three variables that have to be considered in sizing the unit.

• The volume of water the unit is required to heat, measured as flow rate in gallons per minute (GPM)
• The temperature of the cold water entering the unit
• The desired temperature of the hot water exiting the unit.

Groundwater Temperature Impact on Unit Size
In addition to the number and type of fixtures you want simultaneously served by the tankless water heater, you will also have to consider the temperature of your groundwater. And that is determined by where in the country you live.

In the chart above I have delineated what is generally accepted as the cool / warm dividing line of about 55°F groundwater. The colder the groundwater gets the less hot water can be produced by a unit for a given GPM flow rate. This means a tankless water heater in Florida would have to be rated 33% to 50% larger in Michigan to serve the same number and types of fixtures.

Why? Well because the tankless unit heater has to warm the incoming cold water more in Michigan than Florida since the groundwater coming into the unit can be 30°F colder in Michigan (42°F) than Florida (72°F).

For more information on your application and a Free Estimate just give us a call.

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