One British Thermal Unit is the amount of energy it takes to heat 1 pound of water 1 degree Fahrenheit. With appliances, the BTU value refers to BTUs per hour.

Lighting an ordinary match and letting it burn its length radiates about 1 BTU of energy.

Imagine lighting 199,000 matches and you can see the energy released by a tankless water heater in an hour!

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Tankless vs Standard Hot Water Tanks

More and more Canadians are become energy conscious when it comes to energy usage in the home, and a significant portion of energy goes into heating our domestic water.

Tankless, instantaneous, on-demand hot water heat has never been more popular. And why shouldn’t it be? Energy efficiency is reported to be in the 80-85% range (95-97% for the condensing units), tankless heaters only heat the water when you turn a tap on, they’re almost silent running, and CO2 emissions are reduced by 900-1000 pounds per year per average household installation! Time to replace your water heater? You’re of course going to want to replace it with a tankless system right? Well – maybe.

Do your research before you dive in as going tankless doesn’t work for everyone.

What is Tankless?

Tankless is what it says -- tankless -- no water storage tank at all. With a tankless system, when you turn on the hot water tap, a flow sensor within the tankless system detects this flow usually within a couple of seconds. Once flow is detected, the system’s computer tells the tankless unit to come to life, firing up the burners and starting up the exhaust fan. The cold water goes through these burners in a series of small water channels (a heat exchanger) quickly heating the water to a predetermined temperature (also continually monitored by the computer). Once appropriately heated, the hot water is sent on its way to the open faucet. When the faucet is closed, the flow sensor notifies the computer that flow has stopped, which in turn shuts down the burner and goes back to sleep until you turn the hot water faucet on again.

This flow that we’re speaking of is also important when considering a tankless unit’s practical use. Various tankless models are designed with various levels of maximum flow. This flow is measured in GPM (gallons per minute) for a set temperature rise. Many tankless units considered to be multi-bathroom use capable, can produce 9 GPM of heated water with a 1.67°C (35°F) temperature rise. This means that if the cold water entering the house is 4.44°C (40°F), the unit is capable of “instantly” heating it to 23.9°C (75°F) at 9 GPM of flow. This same unit would also be rated at approximately 7 GPM with a 7.22°C (45°F) temperature rise, so it can keep up with a solid 29.44°C (85°F) (about the temperature of a swimming pool) at 7 gallons per minute of flow. 

You’re probably wondering why we’re boring you with this but it's important to understand this before going tankless! You probably like to have a nice hot shower (about 40.56°C; 105°F) so the tankless unit will need to raise the water temperature 18.33°C (65°F). To accomplish this temperature rise, we can guesstimate the flow rate would be around 3½ to 4 GPM. Thankfully, my shower head only allows 2½ GPM of flow, so I’m in the clear by 1 ½ to 2 GPM. Fingers crossed that no-one turns on a dishwasher or washing machine!

Since you likely currently have a typical old-fashioned hot water tank, let’s look how that works. When you turn on a hot water tap, water flows from your hot water tank (that is already filled with hot water) to the faucet which begs the question: which system is truly “instantaneous”? No computer, no fan, no waiting for burners to come on to heat and no flow reduction based on temperature demand. It’s full flow all the way at 60°C (140°F). A standard 50 gallon hot water tank can easily handle simultaneous usage – showering while running the washing machine or dishwasher -- without runing out of hot water. Flow limitations for a standard hot water tank system is dependent upon the size of your water line, not the water heating capability.

Energy Requirements

Tankless heaters have no time to gradually heat the water, it needs to heat the water fast, efficiently and now! This is why a typical gas tankless heater runs at a whopping 199,000 BTU. Thankfully, it only fires on demand, but when the demand is there it FIRES! If you have an hour long shower, its firing for an hour long. A typical hot water tank relies on its storage (usually 50 gallons) and an extended recovery time (30 to 40 minute range).

Energy Efficiency

Most tankless units are energy efficient within the unit themselves. I mentioned before that typical tankless units run at 80-85% efficiency and the higher end condensing units upwards to 97% energy efficiency rating. What may surprise you is some natural gas hot water tanks have energy efficiency ratings as high as 95%. Some commercial hot water tanks are rated as high as 99.1% efficient! Modern hot water heaters are much more efficient than they used to be. If you put your hand on the side of a modern hot water tank that’s full of 60°C (140°F) hot water, the tank shell isn’t even warm, it will feel cool to the touch.

Insulate your hot water lines!

The greatest culprit in heating loss comes not from the heating system used to heat the water, but rather from hot water lines in the house that aren’t insulated. If you have a tankless water heater sending hot water down 50 feet of un-insulated water line, it loses energy the whole way along the line until the pipe is heated up to the same temperature as the water inside it. This is why the water seems to gradually get warmer until finally its hot. The same is true for typical storage hot water tanks. The tank can be as efficient as can be, but if the water lines aren’t insulated, it must waste energy heating those lines up before you finally get the full benefit of the hot water. If you have un-insulated hot water lines in your house that are also part of a recirculation system, the recirc line will actually heat your house, albeit very inefficiently.

Final thoughts

The biggest plus that I can give to a tankless system is that is takes up less space. It hangs up very nicely on the wall. When installed correctly, it’s a clean looking unit. However, by the time you’ve also installed the “buffer” tank, the space savings start to dwindle. When installed correctly, a tankless system can be as efficient as a high efficiency storage tank, but the installation price is certainly higher, and you end up having a water storage tank anyhow. Tankless is very trendy right now, and yes we do install them, but you might want to talk to us about high efficiency water storage tanks that will save your pocketbook as well as the environment. If you’re convinced a tankless system is right for your situation, call us today for a free quote.