Tankless Water Heaters... has their time finally come?

For decades tankless water heaters haven't been worth the effort to install due to our artificially low cost of natural gas in the USA and the high price of tankless heaters. Tankless water heaters have dropped to under $1,000 while tank water heater prices have continued to climb. Are tankless water heaters worth rethinking?

I have found 3 basic types of tankless water heaters:

1: Non-modulating with battery powered igniter such as they use in Europe. These can be bought in the US for under $230, and use 1/2" gas lines. Most will require an vent upgrade to 4" B-vent. 54 -87% efficiency.

2: Modulating tankless that automatically adjusts the burner output based on temp rise and water flow. They sell for about $550 but must either be mounted outdoors or require very expensive Stainless Steel venting. Most require upgrading gas lines to 3/4". 82% efficiency

3: Condensing that can vent with ordinary PVC pipe, cost just under $1,000. Also requires 3/4" gas line and condensate drain. 95% efficiency.

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HPWH are the least efficient when demand is greatest. As temps drop in the winter, HW demand increases. Incoming water temps are at their lowest and there is less heat available in the garage/basement/wherever WH is located.

That really depends on your location.  Northern climates yes,  but Hawaii,  or climate zones 1 or 2,  the difference is small compared to the gain.

If the house is in a mostly cooling climate, with humidity - the HPHW can move some of that heat from the room into the water.  It can also provide some limited dehumidification.

Within in perhaps five years we may be seeing the CO2 based HPHW, which can run at higher water temps,  with even higher COP's.  As more of the utilities move off of coal to NG, or if they complete LNG export facilities - you can expect the price of NG to increase.  And the electric HW tank options may become more attractive -- even over the tankless heaters.


I find most tankless gas line to small,  


Most do not ramp up to give top BTU rating, with small gas lines.  Then get limed up so do not getting full range

Absolutely!   I sometimes cringe when I've seen some of the DIY tankless installations,  they could not have pulled a mechanical permit and done the sizing calculations.  

And the cost of changing the gas line in the house can easily be equal to or double the cost of the tankless.

It really is very customer / application dependent.

This seems like discussion about how to make the Emperors suit more elegant.  

But maybe we need to move this conversation from 2004 to 2014 first:

  • Navien - negative pressure gas valve, no gas pipe change required.
  • Navien - buffer tank and internal or external recirc, no cold slug, no purge, no wait.

But is the juice worth the squeeze?  Where's the beef?  ENOUGH talk about "combustion efficiency" or "recovery efficiency", those are abstractions unless you connect to consumption, cost, and savings.  And when you do, the whole discussion starts looking pretty silly.

We have low flow shower heads, use cold for laundry (and have front loaders even if we don't).  Our hot water consumption continuously drops, and with it drops the opportunity to save with some non forward looking " efficiency analysis."

At 8000 miles a year that Prius doesn't justify on savings alone.  Next year when you only drive 5000, that statement becomes even more true.  If you bought it assuming 20,000 a year your results are WAY off your target.

Midwest energy recommends electric - plain jane simple electric - to clients unless they have 5-6 occupants.  Electric is the energy that gets CLEANER with time.  Its the energy consumers can cleanly, easily and cost effectively produce themselves.

I know, boy children like nifty toys.  I think Navien are cool too.  But plain jane electric solves a lot of problems, removes one more combustion appliance, and leaves $ free for better effect elsewhere.  

Put money where it matters.  We must serve client best interests, leverage their opportunities, not squander them.  

Precisely Ted,

Demand reduction trumps production efficiency every time because its forever!  

Still love the hybrid electric (Heat Pump) water heaters though as you get the best of both worlds, presuming you don't have access to low cost natural gas as many of us in more rural locations don't.

If I go with another tank it won't be an expensive direct vent model. I'll most likely just buy the one they have on sale at the big box store for $400 or so. Easy swap out, no venting/gas line changes.

And that really is a very good point.   

I have friend/relative that really seem to like tankless, but when you ask how much longer they expect to stay in the house... they don't know.  I expect less than ten years.  If they stay only three or four years - they would never fully recover their cost of the tankless.

While it doesn't seem like much,  a tanked gas heater (.62 EF) can had quite a bit of heat into a basement.  If you've lost power during a winter storm.. that tiny amount of additional heat can sometimes help keep the pipes in the area from freezing.  Of course it doesn't help with the distant lines, or lines in the wall, etc.  But I've seen a couple of cases where the tank was near the well pump's storage (air tank) and that happened to be area that doesn't freeze... during extended loss of power.  (well doesn't work) but when power is back, there is some hope for cold and perhaps hot water.

Sometimes we try to squeeze too much energy savings out of things and forget that the "waste heat" was providing some functional benefit in areas we hadn't thought of...

Low efficiency natural draft water heaters have all kinds of unmeasured costs and overstated benefits.  Once you've seen utility bills from a few hundred houses, the pattern becomes clear.  Devices that inefficiently burn a product benefit those selling the product.  

The gas companies have done a great sell job on how much gas appliances "save" that people are chasing pennies thinking they are chasing $20 bills. 

 If you've lost power during a winter storm.. that tiny amount of additional heat can sometimes help keep the pipes in the area from freezing.  Of course it doesn't help with the distant lines, or lines in the wall, etc.  But I've seen a couple of cases where the tank was near the well pump's storage (air tank) and that happened to be area that doesn't freeze...

Dennis, that smells like FUD.  Fear, uncertainty, doubt.  Fuel for irrational decisions.  Not good emotions for driving smart decisions, in fact when these are present there is high likelihood of bad decisions and abuse.  

"You need to heat the earth so when the zombie apocalypse comes you have hot water."

The fallacy here is excluded middle.  Using extremely unlikely events to sell very expensive insurance.  All of us fall prey to this low quality thinking from time to time, both on the delivery and the receiving end.  

Awareness, simply being on the lookout, is powerful key to avoidance.  Once we see it, if we have integrity, we stop.  I'm assuming everyone here has high integrity, that I'm not wasting my breath.  Awareness - makes me think this is NOT how I want to sell to my clients, and it's not how I want to be treated by consultants & experts I engage. 

If you have pipe freeze risk, fixing the house is much cheaper and more effective than heating the ground.  It will help prevent ALL the pipes from freezing, not just the ones near that water heater that is losing so much heat to the basement and up the chimney.  

A tight, reasonably insulated house without a leaky basement doesn't have pipes freeze even when power outages go from hours to days, and the likelihood of days worth of outages is likely as "getting struck by lightning on the 18th hole after getting a hole in one".  

Tom, whether there are chimneys or not doesn't matter when you have electric hot water...

The small heat loss from the heater and keeping the area warm is exactly something that I have observed multiple times.  It only extends to that service area - but it certainly works.  The point is that tankless doesn't provide the same effect.  A tanked electric heater offers the same added warmth.  No FUD,  just simple observation.   I am not suggesting that this is used to heat the house - instead a simple observation that sometimes minor things are over looked.  If that service area (sometimes a garage) doesn't have heat in it... it may need something added to prevent the freeze up of heaters if the technology is changed.

In climate zones 5 & 6, the tankless heaters also can have some pretty nasty wind induced drafts through them which can result in the heat exchanger freezing.  I know of at least one case where that occurred.

No - end of the world - just some rather surprising real world observations.  I could possibly add data loggers on one or two sites in future... but I don't see the need.  The house is old - the owners are old,  my suggestion was simply be prepared to replace the tank with the same type in the future - don't spend the money to upgrade the tank to another technology.  Instead the pipes were upgraded to pex with home runs and lots of insulation.


A combustion device that requires continuous make-up air means the device is sucking unconditioned air into the building.  This is a latent energy, sensible energy and control penalty.  It may also have numerous other penalties including health and safety.  

Vague quantifiers like "small heat loss" makes me think of these auto commercials where the savings is "HU-GE".  Can you put HU-GE on a deposit slip and take it to the bank?  

When you refer to the loss it is somehow big enough to matter when it comes to the fictional freezing pipe scenario, but inconsequential when it comes to cost or waste.  And somehow this "heating the basement" is identical to the "benefit" of an electric tank that has insulation covering 100% of it's surface and no metal chimney pulling cold air up off the cold floor, putting heat into it, then sending that heat outdoors?  

Making decisions based upon vague words like "small heat loss" is simply not an acceptable way to treat other people's money.  If you are a professional doing this, stop, or you risk having your reputation seriously suffer.  

Most people want to know what things cost.  Net cost.  When there are rebates, or energy savings, they want net cost.  Overstating or giving inaccurate savings kills consumer confidence.  

Promising $1 and delivering 50¢ is NOT going to build consumer confidence: 


When it comes to conversations of "energy efficiency" we need to abandon vague terms.  Is it clear what a slippery slope they create?  Without clarity there is no accountability.  Without accountability, integrity follows.  When an industry has no integrity, consumers have no trust. 

What is your background so I can speak to your level rather than above or below it.  Do you have any experience with building envelope, building science, modeling, or measurement and verification of your model results?  

I am an engineer.  And yes I do understand latent and sensible heat.  And I do have building science and air quality experience.

The authors article was about tankless is it time to switch.  My comments have been about the observations that it may/or not may make sense to switch.  I have deliberately avoid a discussion about making the building envelope more efficient -- because that simply is out of scope with Bob's original blog entry.

I am also very astute on steps that can be taken to reduce energy consumption.  That wasn't the point of Bob's original blog.

Re-read my comments,  I have been trying to add things to consider when looking at tankless vs tanked -- not justify a decision.

As for the comment about Midwest power.   I live in the Seattle area.  My local utility has both gas and electric- they rebate for customers to swtich from electric to gas.  In Portland (150 miles south)  Portland General Electric is only a electric provider,  I've had discussions with engineers/(execs) about heaters in their service area - why not fuel switch,  or HPHW (which do work well in the area) and the comment had been "we are an electric company, gas is our competitor"  And also in their comment was the reminder that they prefer demand response resistance heating instead of HPHW because of the value stream (sales of electricity).

There are lots of issues if you go beyond Bob's blog entry.  It is just easier to focus on the pro's and con's of tankless vs tanked.  And for both there are a number of variations of heaters.  electric flash heaters,  gas flash heaters,  tanked - HPHW, resistance and gas low eff, direct vent and condensing.

When comparing - you need to look at the location that the unit will be installed, its environment (service area of the house), and if the occupants will see a payback.  And the payback needs to include all of the balance of system items that may need to be included if you change heater technologies in the house.


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