Tank vs. tankless hot water heating

September 11th, 2007
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Through the many houses and places I’ve lived in over the years, I’ve experienced quite a few different hot water systems. Everything from a kettle when I was a fisherman (that was rough), to the solar shower bag and wood stove when I was in the outback and the more traditional types – electric tank, gas tank and tankless water heaters. I haven’t had the pleasure of owning a solar hot water service as yet, but I regularly drool over my neighbor’s!

If your hot water service is on its last legs and solar is out of your reach too; consider a tankless water heater.

Traditional tank systems have a couple of major drawbacks – firstly, they tend to wear out in under a decade; so millions of these things wind up in landfill annually. Another biggie environmentally speaking, not to mention ongoing costs – is energy consumption. Heating water accounts for over 20% of residential energy use in the USA and up to 40% of energy used in Australian homes.

All that energy has to come from somewhere and usually it’s from fossil fuels (gas) or coal-fired electricity generation. For each kilowatt of electricity produced from coal, around 1.5 pounds of carbon emissions emissions are created. Then there’s mercury, nitrous oxide and sulfur and all sorts of other toxic goodies thrown in as well.

The energy hog aspect of tank based hot water systems is due to the fact that much of the time they are cycling on and off to maintain water temperature. While you can reduce/retard the amount of heat escaping using a water heater blanket; you (and the environment) is basically paying for heating water that you aren’t using at that moment – this is called standby heat loss.

Additionally, each time you use the hot water, cold water is flowing into the tank which lowers the temperature of water that had been heated; therefore even more energy is then required for reheating.

The tankless water heater

Tankless water systems work very differently by heating water on demand. A tankless hot water service applies heat directly to the pipe after being automatically activated when a hot water valve is opened. Once engaged, the heater delivers a constant supply of hot water. Tankless water heaters are continuing to gain popularity and now account for over 50% of all the new domestic systems installed in Britain.

Tankless hot water savings

While the initial outlay for a tankless water heater can be double the cost of a standard tank water heater – sometimes more; it should pay for itself in just a few years or less. The hardware should also last twice as long as a tank system. The average family can expect to save between 30 and 50% on water heating related energy bills each year. Both these points make it not only good for your wallet to switch to a tankless system, but good for the environment too.

Disadvantages of tankless

Aside from the initial cost, there are a few other common disadvantages of a tankless system.

a) Tankless systems are somewhat limited in the quantity of hot water that can be produced simultaneously. I don’t remember this being an issue with the gas tankless system that we had in our last house (family of four).

b) I’ve read reports that hot water can take longer to reach faucets that are some distance away from the unit. Again, this is something I didn’t experience with our system.

Something very important to check into if you’re replacing an existing system is if your plumbing, gas/electricity systems are compatible with a tankless setup. While there are energy savings in using a tankless, they do use a lot of energy in a short space of time in order to produce “instant” hot water. This may mean some (expensive) modifications are required to your hourse – so it’s best to get professional advice from a plumber first before purchasing.

Unless your current water heater is a voracious energy hog; given that a tankless system isn’t cheap; consider keeping it until the end of its service life. There’s plenty of other things you can do around your home to minimize environmental impact in the meantime.

Something else I noticed when researching this article is that within the water heating industry, there’s definite sides – those in the industry who love tankless and those who seem to absolutely hate it. Reading some of the debates was a bit like reading arguments between car lovers over different manufacturers. My advice is that if you are considering replacing your hot water service with a tankless system – make the plumber you consult is not prejudiced either way so you’ll get a balanced professional view of what’s best in your circumstances.


Michael Bloch
Green Living Tips.com
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