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Tankless water heaters and what you need to know

AAA Heating & Cooling con provide you with the right water heater for you and your family needs, here are some pros and cons with Tankless water heaters.


  • You can’t put a price tag on going green.  There’s no dispute about this – Tankless water heaters use less energy.  Doing the environmentally responsible thing doesn’t always have a measurable return on investment.  I mentioned this last week, but only briefly.   Not everything we spend money on will give us a return on our investment – we all know that.   After all, what’s the payback period on a sofa?
  • Tankless water heaters make sense for a cabin / vacation home.  Traditional water heaters have a ‘vacation’ setting, but I’ve heard it’s a bad idea to use this setting, because it greatly increases the potential for legionella pneumophila growth.   Having a Tankless water heater installed in one of these settings would result in much more than a 25% fuel savings.
  • Energy Star Tax Credit.  This $300 tax credit which includes Tankless water heaters expires December 31, 2011.   You can read about it here – tax credit.  I’m guessing we’ll see another one show up when this one ends.
  • Fuel costs will continue to rise.  As we all know, fuel costs continually increase.  If fuel costs tripled in the next 20 years at a linear rate, a Tankless water heater would actually give me a return on my investment.


  • Low water flow = no hot water.  If there isn’t enough hot water flow, a Tankless water heater just won’t turn on.  One person even commented that they had to turn on the hot water faucet at their bathroom sink and leave it on the entire time they took a shower, or they couldn’t get hot water.  For instance, Rinnai Tankless water heaters need at least .6 gallons per minute, Bosch needs .65 gallons per minute, and Rheem at least .4 gallons per minute of hot water flow to kick on.
  • The cold water sandwich.  If you think gefilte fish sandwiches sound bad, just try one of these.  The cold water sandwich effect is something that happens with every Tankless water heater.  When the faucet is turned on, off, and on again, you’ll end up with a slug of cold water interrupting your hot water flow.  Some Tankless water heaters require the call for hot water to last for at least three seconds before the burners turn on, so there can be several layers of hot and cold water in the pipes.  This doesn’t exist with traditional water heaters.
  • The long wait for hot water.  One already has to wait nearly forever to get hot water at their kitchen sink, but the wait would be even longer with a Tankless water heater.  One interesting solution that I heard a plumber mention was to install a dedicated 3/8″ supply line to his kitchen sink from the water heater.   He claimed that this still provided just as much water flow, and made the wait much shorter.  I’ve considered doing this at my own house, although this is technically a code violation.

A small tank-type water heater stops the cold-water surprise. Adding a 10-galon electric water heater to a thankless model creates a buffer to eliminate the section of cold water left in the Tankless heater’s heat exchanger. If located near the bathroom, the tank also can reduce the wait. Another solution is presented by Navien, which has a small tank inside the Tankless water heater to help eliminate the cold water sensation. AAA Heating & Cooling has worked with our customers to help solve our clients concerns of long waits for hot water. Contact AAA Heating & Cooling for you complementary consultation about Tankless water heaters.


Design/IAQ Specialist
Email: michaelt@aaaiaq.com
Phone: 503-284-2173 Ext. 5507
Web Site: https://aaaheatingandcoolinginc.com