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Tankless Water Heaters.

Although tankless water heaters are the standard in Europe and Asia, many North Americans are baffled by the concept of hot water without a tank. This How To will focus on gas fired tankless water heaters (TWH's).

Why tankless?
Imagine a houseful of guests (or worse - teenagers) who all want to take showers. A standard tank hot water heater will be great for the first couple of showers (maybe) and then it's a long wait for more hot water.

With a tankless hot water heater (see sizing requirements below) you can expect to take 2 showers simultaneously with no time limit.

Also, for the energy and fiscally conscious among us, tankless water heaters will save money from day one, and by lasting longer give you a lower life cycle cost. With traditional tanks the heater will operate periodically even though no hot water is being used due to the tank's standby losses. These losses are due to the heat conducted and radiated from the walls of the tank and through the flue pipe. They represent 10% to 20% of a household's annual water heating costs.

Here are some important advantages to going tankless:

- Convenience: Tankless hot water heaters do not run out of hot water. They keep producing hot water for as long as the hot water tap is open.

- Energy Cost: Tankless hot water heaters cost a lot less to run than a traditional tank. A typical tankless unit will run at 85-90% overall efficiency, compared to a typical tank that will perform in the range of 55-60% (including losses).

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- Longetivity: A tankless unit will outlive several hot water tanks.

- Direct venting: Some of our tankless heaters have direct venting, which means that combustion air is taken directly from outside (through a pipe), and does not draw additional cold air through cracks into your home.

- Space saver: TWH's are very compact.

- Bacteria: TWH's store only cold water, reducing the risk of bacteria growth.

Tankless Sizing:

The simple method for sizing: If you require more than 1 simultaneous use of hot water - shower, sink, washing machine, etc., then we suggest using a 190,000 BTU/hr or higher tankless water heater.

The engineer's method:
Flow in gallons/minute = input BTUH x efficiency / (500 x (mixed hot water temp - cold water temp))

Here are some typical amounts of hot water use (source: EREC Brief):
- Faucets: 0.75 gallons to 2.5 gallons per minute.
- Low flow shower heads: 1.2 gallons to 2 gallons per minute.
- Older standard shower heads: 2.5 gallons to 3.5 gallons per minute.
- Clothes washers and dishwashers: 1 gallon to 2 gallons per minute.

Things to be Aware of:
1. Make sure you have large enough natural gas or propane piping to the heater. The exact size of pipe depends on the distance from the pressure regulator and the BTU input of the heater. See the installation manuals for specification tables.

2. Some of the heaters will require category 3 piping which is stainless steel. This flue pipe is not cheap, but the flue piping can be minimized by venting out horizontally.

3. Hot water will come out of the THW unit almost immediately after a tap is opened, but there is a mininum flow rate that is needed to start the burners. This would only be a problem if for some reason you routinely need just a trickle of hot water.

How Tankless Works:

1. When you open a hot water tap, cold water enters the heater and triggers the heating elements or burners. Your hot water tap acts as an ignition key for the energy used to heat the hot water you need.
2. The water is heated as it flows through the heating elements or heat exchanger. As the water flow varies, the unit adjusts the heating elements or burner flame to maintain a constant temperature and maximum energy efficiency.
3. When the hot water tap is turned off, the heating system also turns off.
(Illustration and explanation courtesy of Controlled Energy Corporation)

More Links:
- Stainless Steel Flue Venting

As always, if you would like to ask more questions about this or other technical topics give us a call at 877-711-4822 - 9-5 PST. Live people for technical and sales support - an Internet first!