Tankless water heaters: an empty promise?
Experts weigh in on on-demand hot water heaters
By: Kevin Ma
| Posted: Saturday, Sep 29, 2012 06:00 am
When he moved into his new place a few years back, my brother Mike was pretty pumped about his tankless hot water heater.
“The theory makes perfect sense,” he says. Regular hot water tanks waste a lot of energy because they have to keep their contents hot all day. This tankless or on-demand system would only fire up when someone opened a hot-water tap, meaning he’d save a bundle on gas.
It was also fast. “In the morning I’d turn the shower on, and in maybe 15 to 20 seconds it’s up to full temperature already,” he says — a far cry from the minute-plus wait at our parents’ place.
And it worked great up until about a year ago, he says. Now he’s changing filters, cleaning sensors, and calling in plumbers to try and get the dang thing to work — it’ll make the water hot at first, but then it’ll nosedive 10 to 15 degrees until he turns the tap on and off again. “It could be an electrical problem. It could be a plumbing problem. It could be a construction problem. I don’t know.”
As an eco-nut, I was disappointed to hear this news. Had Mike bought a lemon, or were these tankless heating systems an empty promise?
Efficient, but expensive
To find out, I called Mike Paul, a plumber and owner of Edmonton’s Up-to-Code Mechanical Plumbing and Heating Ltd. who has helped install hundreds of these systems over the last decade.
Regular hot water tanks are like kettles: they keep a large amount of water hot all the time, and they have to keep re-heating it the longer the water sits unused. That can account for about 40 per cent of your household gas use, Paul says. Like kettles, those tanks can also run out of hot water.
Tankless systems are more like radiators, Paul explains: they run inbound water through gas-heated coils, warming the water as it flows through. “As you need water, it heats it.”
This lets tankless systems use about 30 per cent less gas than regular ones, according to a 2009 study by Natural Resources Canada — enough to save a typical Alberta family $104 a year. It also means your water heats up really fast and stays hot, so long as you have natural gas.
These systems cost about $2,000 more than regular ones, Paul says, but you get that cash back in energy savings in about 10 to 15 years — faster if you use a lot of water. “If it goes into a car wash, the payback could be as little as two to five years.” Solar hot water heaters are even more efficient, he notes (as they require no gas), but are also more expensive.
Most on-demand water heater buyers tend to be concerned about energy efficiency, Paul says, and put the systems in summer or net-zero homes.
Chris Hanstock, an energy-conscious faculty services officer with the University of Alberta’s biomedical engineering department, says he’s had one since 2004. “We’re pretty water conscious, so we tend not to use a lot,” he says. “Our gas usage throughout the summer is virtually zero.”
But tankless systems also require a lot more maintenance. “They’re complicated pieces of equipment,” Paul says, and contain many more sensors and valves than traditional heaters.
He suspects my brother’s problems might be due to a bad sensor or a clogged air intake. “Our water’s fairly hard in Edmonton,’ he notes, which can cause minerals to gum up various components. There are also some brands of heaters out there that are notoriously unreliable.
You also have to change some of your habits, Hanstock says. Since the heater doesn’t kick in until it senses a certain amount of flow, you can’t flick the hot water on and off while you do the dishes — if you do, the heater will keep cutting out. He now knows to fill one sink with warm water instead.
You might also run into the “cold-water sandwich” effect, Paul says, where you get a burst of colder water in amongst your hot. This happens when there’s still some residual hot water in the pipe that runs out before the heater has time to warm the new flow. “The unit has to fire up,” he says, so you might get a few-second-long cold spot soon after you turn on the shower.”
On-demand systems aren’t for everyone, Paul says. They’re most useful to big families that use a lot of hot water and to folks who want to save energy. Don’t even bother with them if you hate doing maintenance.
And do your homework, says Mike, who is still trying to get his unit to work. “Get the right brand and get it installed properly.”