Condensing, tankless hot water heater (left) with drain water heat recovery unit.
The decision is usually thrust upon you. Shower water goes luke warm, or worse, stops altogether one morning. If you're lucky, the basement won't be all wet when you go downstairs to investigate. Yes, the hot water heater has died.
In the hectic days following, you need to make a decision quickly. If long-term energy security and environmental impact are priorities for you, here is a short guide to buying a new hot water heater.
Note: this post was co-written by a good friend of mine who is, in my mind, one of Edmonton's most knowledgeable experts on energy efficient retrofits. He recently installed the water heater shown above in his own home.
Solar Hot Water
The most efficient way to make hot water uses solar collectors, but if you don’t want to (or have the time to) go the solar route, your best option is to use our plentiful and cheap natural gas. Although electricity provides 100% efficient water heating, the electricity itself was generated at 30%-50% efficiency, often using dirty Alberta coal.
Tankless Hot Water Heaters
Using natural gas, the most efficient choice is a condensing, on-demand hot water heater (seen above). This means that there is no tank, and therefore no standby heat losses, and the combustion of the natural gas to heat the water is the most efficient. They have an energy factor (EF) of 0.92-0.96, and they cost around $3000-4000 installed. The combustion gases are near room temperature and are vented directly outside through the basement wall often using PVC pipe.
Predictably, I (Conrad) endorse the above choice. Long term, people! Think long term.
The next most efficient choice is a regular combustion, on-demand hot water heater (no tank, but the combustion is less efficient). They are vented up an existing furnace/hot water chimney or out the side wall using metal pipe. They have an energy factor of 0.82-0.84. (we have no info on costs - anyone?).
Hot Water Tanks
Next up are condensing hot water tanks. Their combustion efficiency is in the 96% range, but because of the standby losses of the tank the energy factor is around 0.83. They cost around $4000 installed.
Finally, there is the regular old hot water tank, which has been around for more than 100 years. Some are insulated better than others and energy factors range from 0.53 to 0.66. (again, no cost info, although this is certainly the cheapest option).
Tankless = Durable
Besides energy efficiency, a compelling reason to choose a tankless heater is durability. Every tank will eventually corrode and spring a leak. The difference in life spans between tank and tankless heaters is significant. In fact, "Expected life of tankless water heaters is 20 years, compared to 10 to 15 years for tank-type water heaters" (source).
So there you have it. To me, tankless seems like the way to go, but obviously every situation is different. If you do decide on a tankless unit, Edmonton contractors are much more knowledgeable about them than they were just a few years back. Also, make sure to get at least two quotes, as I have heard of $1000 differences for installation and purchase of the exact same unit.
* The Energy Factor of a hot water heater is based on three factors: 1- the efficiency with which the combustion energy of the natural gas is transferred to the water; 2- the heat lost due to storage; 3- cycling losses due to startup and shutdown.
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