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Dangers Of Tankless Water Heaters

Tankless water heaters are a great choice since they are generally much more energy-efficient than conventional water heaters.

Many people are replacing their old tank water heaters with tankless models to take advantage of the tax credit.

Tankless water heaters are as safe or safer than conventional water heaters when installed properly. Correct installation of tankless water heaters is very important due to their extremely high momentary energy consumption compared to conventional water heaters.

There are some things that are unique to tankless water heaters and others that are common among all water heaters.

Poor DIY Installation

Many people enjoy DIY projects around the house. I am one of them.

Some projects can be done without any experience and others require a lot of research and some previous experience.

Installing a tankless water heater is not something I consider a DIY job.

Whenever I start a project I think to myself. What will happen if I mess this up completely? If the answer is not acceptable to me, I will not do it.

There are so many things to take into account that it is best to turn to a professional plumber.

I will list just some of the things that must be taken into account for a successful install. I’m sure there are many more, but those are just off the top of my head.

  • Wire sizing
  • Fuse sizing
  • Phase balancing
  • Actual electrical connection to the water heater
  • Flue connections
  • Ventilation

For an electric tankless heater, the connections must be excellent. Some of the water heaters are 30+ kw. This means a lot of current will flow through the cables.

If any of the connections are poor, they can start a fire.

Air In The System Overheating Heating Elements

For a tank water heater, a little air in the system is no big deal. Since the heating element is at the bottom.

Unless the entire tank is empty the heating element will be submerged in water and will not overheat.

However, it is a different story for tankless water heaters. The heating element on tankless water heaters can be 10 times more powerful compared to conventional water heaters.

This is to be able to supply the hot water instantly. A conventional water heater has time to warm up the tank of hot water over many hours.

There is a lot of heat energy that must be dissipated in a very short amount of time, if the heating element is not submerged in water, it will quickly overheat and over time can even fail.

The most common way water heaters run dry is when first installed. There is an easy way to make sure that all of the air is purged out of the system.

Connect the cold water source to the water heater and open several hot water faucets to purge all of the air out of the system. This must be done before turning on the water heater for the first time!

Another way for air to end up in the system is when doing plumbing work. This can introduce air into the system. If this air pocket happens to stop in the water heaters element, it can cause permanent damage.

This is why it is always a good idea to purge air out of the system every time pipes are opened up.

Overloading The Electrical Circuit

A electric tankless water heater draws about 4 times more current compared to conventional water heaters.

When not accounted for this can cause problems when trying to use other high-powered appliances such as ovens, hobs, and vacuum cleaners.

Below is a table of current requirements for common tankless water heaters and regular tank-style to illustrate the massive difference.

Water heaterAmpskw
30-gallon tank water heater 240v13 A3.2
80-gallon tank water heater 240 v18 A4.5
1.55 GPM tankless 240v33 A8
2.54 GPM tankless 240v54 A13
4.7 GPM tankless100(3 x 40 A)24

As you can see from the table, tankless water heaters require quite a bit more amps when compared to conventional water heaters.

If the electrical system is not designed properly they can easily overload the circuit.

For example:

40 Amp circuit breaker

15 GPM tankless water heater installed in this circuit. This draws about 33 amps. This means if someone were to connect a vacuum cleaner to the same circuit, the breaker would trip.

CO Poisoning From Gas Water Heater

Anything that burns fuel, be it furnace, water heater or fireplace produces Carbon monoxide. During normal operation, this poses no risk. The CO is exhausted out via a chimney or other vent.

So this is not strictly a danger unique to tankless water heaters.

illustration of Symptoms of Carbon Monoxide Poisoning

Carbon monoxide poisoning is extremely dangerous since the gas is odorless and colorless. Although steps can be taken to ensure safety.

The water heater can even be placed in a bedroom if safety precautions are taken.

If you have a fuel-burning appliance at home make sure that you have a Carbon monoxide detector (amazon link) as it might save your life.

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