Tankless, Point of Use and Mini Storage Water Heaters
In Europe ,Point of Use tankless water heaters are very common in older buildings. There are also Point of Use Mini Storage Water Heaters. I am trying to get a sense of the install costs and operating costs compared to systems more commonly used in the US. To me they seem intuitively better - no need to install or insulate hot water pipes from a central water heater (domestic water piping is cut in half), no loss from storage of hot water in a central or remote tank, water is only heated where it is needed and when it is needed.
From Energy.gov: Tankless or Demand-Type Water Heaters . This site states:
For homes that use 41 gallons or less of hot water daily, demand water heaters can be 24%–34% more energy efficient than conventional storage tank water heaters. They can be 8%–14% more energy efficient for homes that use a lot of hot water -- around 86 gallons per day. You can achieve even greater energy savings of 27%–50% if you install a demand water heater at each hot water outlet.
This ecomfort.com post on a Point-of-Use Water Heater Buying Guide makes them seem like a solution only for unusual circumstances
This hot-water-heaters-reviews.com post titled Point-of-Use Water Heater Review & Buying Guide indicates that they are not for applications with a high hot water demand, but they do not state why.
ThisOldHouse.com has a more detailed article titled Tankless Water Heater: What You Need to Know Before You Buy but it is still hard to quantify the pros and cons.
BobVila.com has more information in a post titled The Best Tankless Gas Water Heater for Your Home
In doing the math, if 3 people take a 15 minute shower each day at 2GPM, that would be 90 gallons of hot water, more than the 86 gallons per day listed from Energy.gov for "a lot of hot water" for the showers alone. That may be why these solutions are not more efficient than traditional central hot water.
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