Is an On-Demand Water Heater Right for Me?

Posted by Ben Thompson on 12.15.10

For a lot of us it just seems silly to heat water all day long in a big tank to dose it out just at the beginning and end of the day.  On first glance it just makes more sense to use an on-demand water heater.  Here is a brief checklist of some of the hurdles many of our clients have been struggling with over the last 5+ years and honestly it keeps coming back to installed cost and their expectations of  "unending hot water."  My experience - I have a conventional water heater in my home.   I wish I had an on-demand water heater but it doesn't quite make sense in my home.  I first stayed in a house using on-demand water heating in Japan a few years ago and loved it!

Hurdles to Consider:

  1. Peak demand - If you have more than 2 people showering at a time you may hit peak demand issues.  If you live in a busy (4+ person) household with everyone trying to get out of the house at the same time there is a lot of hot water being consumed in a short period.  If you're okay with staggering just one or two activities you are all set.  Where this hurdle came from is the unrealistic expectation that one will never run out of hot water again.  The starting water temperature has a huge impact here.  My well water is coming into my house at <45 degrees right now (not taking into account water having a chance to warm up inside the pressure tank in my house).  Adding 70 degrees to it in a matter of seconds is very hard.  If it comes in the house at 55 degrees more water can be heated faster.
  2. Water Quality - If you're on a well (like I am) there is a greater chance of premature wear of expensive parts that one should expect to reduce the total service life of the water heater.
  3. Installed cost - 2 to 4 times the installed cost of a conventional water heater.  More realistically it is a closer gap of 1.5 to 2.0 times the cost of a direct venting tank water heater.  A 3/4" gas line is required by most units and we run into a majority of conventional water heaters being currently fed with 1/2" gas supply line.  The closer to an outside wall the better (prefered is to actually install on an exterior wall) but also consider that the intake & exhaust will need to be multiple feet away from your furnace intake & exhaust or bath fans, etc.  The installed location for an on-demand water heater in my house would not be in my current mechanical room but rather on the other side of the basement closer to the (2) bathrooms stacked on top of each other and a 1 1/2" (HUGE) gas line near there from when our house had a heated swimming pool.  These are just positives that our house has going for it, not necessary for others.  As you have already read, I do not have an on-demand water heater for other reasons.

Benefits Once You've Overcome Hurdles:

  1. Safety - all sealed combustion [high efficiency water heaters and high efficiency furnaces] units exhaust carbon monoxide directly to the outdoors.  A side note for safety, if your home does not have anti-scald shower valves we need to talk about that too.
  2. Energy Efficiency - logically, it makes sense to use just what you need.
  3. Ever Lasting Hot Water at a Calculated Rate - never a cold shower again...never live at home without it. *See Peak demand discussion
  4. Immediate Recovery - IF you do exceed peak demand all someone has to do is change one thing.  One person has to wrap up a shower and everyone else will be happy.  The dishwasher can be put on delay so it runs just after everyone leaves for the day.  The laundry can be done on the way out the door or in the early evening.
  5. Adding a bathroom - If you add a bathroom far away from the existing water heater it could be a fabulous circumstance to add an on-demand water heater to service just that bathroom.
  6. Space savings - by hanging an on demand water heater on a wall you free up a few feet of floor space.

Two Client Profiles:

  1. No kids, city water, budget not the primary driver, natural gas - On-demand is for you!
  2. 4 kids, well, or budget enters the discussion - Stick with a convention tank water heater.

On-demand water heating is the way the world is headed.  I love having this conversation with clients, analyzing their current household and providing them with information relative to their unique home so they can make the decision that is right for them.  I predict that adoption rate of on-demand water heating will continue to increase year after year.

Topics: On the Radio, energy saving, green, hot water heater, on-demand water heater, trend, water heater, on demand, plumbing, rinnai water heater, tankless water heater