Green Calgary

Making the Most of Your Tankless Hot Water Heater

Reader Question

Dear Ashley,

Last year I installed an on-demand tankless hot water heater to replace my old hot water tank and although it seems as though I’m saving natural gas, I have to run my taps for longer to get hot water to them. This water waste really concerns me. I’ve heard of recirculation pumps but I don’t know much about them. Do you have any information or advice?

Thank you,
Douglas

Ashley's Answer

Dear Douglas,

According to Environment Canada, tankless hot water heaters are 10 – 15% more energy efficient than the standard hot water heater tanks. This is because tankless hot water heaters only heat the water when it is demanded rather than always having 45 – 50 gallons of water hot sitting, waiting to be used. One can imagine that keeping the water at 40 0C while everyone is at work or sleeping is not particularly efficient. Heating water when it is needed seems logical enough.

Comparative studies reveal that tankless systems do have big energy savings, saving users thousands of dollars in the long run, but few of the studies address water consumption issues. This isn’t surprising given the comparatively high cost of energy to water, but because water is a major constraint to Calgary’s growth and wellbeing, it is in our best interest to conserve water any way we can. So is it possible to reap the energy saving benefit of a tankless system while also saving water? It seems so.

It is important to keep in mind that both tankless and conventional hot water heaters require that the cold water be purged from the tank before hot water will be at the tap. The farther the tap is from the hot water tank, regardless of the type, the more water that must be purged before the water is warm. Tankless hot water heaters have an extended delay because of the lag in the time that the water starts flowing and time that the heater kicks in. Unless you have a way of capturing and using this water, it is sadly lost to the drain. This problem can be remedied by installing a recirculation pump.

Recirculation pumps keep water flowing through the heater so that when it is demanded it arrives at the tap warm. This has a certain energy requirement. The pump needs electricity to get the water moving, while pushing water though the pipes eventually lands it at the hot water heater, where the water is reheated. Reheating water will require either natural gas or more electricity depending on the type of tankless hot water heater you have. Continually circulating water through the water heater will force it to work much more than is normally required, negating much of the energy savings. This, however, is remedied by selecting a recirculation pump that kicks in by way of a timer or through a switch, either manual or motion sensed. If you need hot water from 6 to 8 AM for your morning routine and then again from 5 to 7 PM for dinner, you can program the pump to kick in for these periods. Alternatively, a motion sensor can be placed in areas where hot water is needed, engaging the pump only when there is activity in those areas. Experts agree that recirculation pumps should be installed at the point farthest from the water heater, as this is the point where the greatest volume of water must be purged before it is hot.

Another option to the recirculation pump is to install a point-of-use hot water heater. These are typically placed at the most distant point of use (or where demand is highest) and can be very effective in saving both energy and water. If, for instance, most hot water is used in the upstairs bathroom, a small point-of-use heater could be installed under the bathroom sink, thereby eliminating the need to run water from the main heater. Point-of-use heaters are common in German homes and provide a good alternative to installing a recirculation pump. It would be wise to speak with a qualified plumber to discuss your options. The Green Plumber Ltd. (403-248-7771), located here in Calgary, is well experienced in this area and may be able to suggest a good set up for your particular arrangement.

Finally, I should note that with a few minor fixture and fitting upgrades and several lifestyle adjustments, great gains in efficiency are possible. This applies to people using a tankless hot water system, as well as those still on water tank heaters. Installing tap aerators, low-flow shower heads and toilets, checking for leaks and insulating the water tank are just a few simple steps a person can take to make the most of the hot water being used. Combining these minor upgrades with a few lifestyle changes, such as washing clothes in cold water and reserving the clothes and dish washers for full loads will result in dramatic water and energy savings. Small adjustments can go a long way in conserving water and energy, even if you are not in the market for a new hot water heater.

Conservingly,
Ashley

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