Thoughts on on-demand / instant electric hot water heaters?

14 Replies

I have a number of 1 BR 1 BA apartments with aging hot water heaters.  I replaced the last one that failed with standard 40 gal electric hot water heaters, but am now thinking of switching to 18kW on-demand / instant electric heaters, at least for the lower apartments.  

Currently it costs my tenants $45 to $50/mo just to keep the water warm in the large storage tank type traditional heaters, which is a significant burden for $550/mo apartment renters.  The units are largely occupied by single people, and I would target any conversions at those units with just one tenant, particularly on the ground floor where the pipe runs are very short.  Power supply is not a problem, as the electric service was upgraded and high amperage 220V panels are just next to the installation area.

Does anyone have experience with tankless electric HW heaters vs. traditional 40-50 gallon HW heaters?  Problems?  Utility savings?  Brands to avoid, and positive recommendations?

We have and electric on demand on our house and I really like it.  I though the unit itself was costly, it was a whole house unit at about 700.00. However we don't run out of hot water and that was a constant frustration before.   We looked at putting them in a multi we have where we pay for hot water and they seem to be pricey for the unit plus the cost of the wiring even though the service was sufficient. I would love to shift the cost of hot water to tenants but the only chance is if the unit cost was much lower.   I can't speak to operating cost differences because we went from oil on demand to electric on demand so of course it went up but not unbearably. I would say 20/month for a family of 4.

I have both at my house (the 90-gallon tank-based unit is used as a backup).  The electric works pretty well on its own, but pulls a lot of power -- mine pulls about 36kW, but even 18kW is a pretty big power suck.  So, make sure that you're certain you have the power capabilities (have you done load calcs across all electric appliances/motors?)...

Assuming power isn't an issue (and you're not paying the electric bill), I think it's a reasonable solution...

I switched over to the small Titans for some 1/1s and are pretty happy with it.  Did have to pull new #6 conductors for the tankless.

For me it makes sense being in South Florida so the temperature rise needed is the lowest possible.

The downside of this is if we have a hurricane and power goes out with a tank HWH you still have 2 hot showers left, with a tankless you are taking cold showers.

I would stay away from tankless water heaters period, especially in a rental.  It most likely won't save the tenants much if any money.  More expensive to put in, more expensive to fix and replace.  

I have small electric ones in my one bedrooms. It cost me about $450 and maybe $100 to install.  They have  a lifetime warranty. I had one for two years and it went bad, I called the company, it turned out all it needed was a new fuse and they walked me through how to open it and replace it. I plan on buying them for my tank systems that are starting to rust out. I have not heard any complaints on power consumption.   

I talked to my plumbing supplier about them.  He said that it is not worth putting them in based on the cost.  He did not feel that they would last long enough to realize the savings. 

You also need to consider whether you have the power capability for these.  They take a lot of power at the moment of need. 

Also, if you are using gas and these are going to be installed indoors, you will need to change the vents to a special and more costly style of vent.

At least that is what I found when I looked into this about a year ago.

Based on the several success stories related by 1BR 1BA multi unit owners above, I think I'll go ahead and install a single tankless heater, and see how it goes.  I will report the results back to the forum.  From researching this topic, one thing I know I'll need to check is the lowest incoming water temperature, so I'll probably wait until February to try to capture the lowest incoming water temp, so I can choose the correct size tankless water heat.  Thanks everyone for weighing in on this topic.

@Ken P.  

Before you move ahead, check the temperature lift capability of the electric on-demand water heaters you are entertaining.   Our experience has been they struggle with the lift required for winter water temperatures in northern climates.

On the other hand, they work find behind a solar thermal storage system which will pre-heat the water, leaving the electric on-demand to handle the final boost of water temperature en-route to a given unit.

1(506) 471-4126

Here in the Phoenix area, we have hard water. My plumber said that three years is about the max that a tankless will last unless you are running the source water through a softener.

I have 5 yrs experience plumbing, and now have two years electrical experience as well.   Tankless water heaters can be a good option in the right situation, but as a general rule stay away from electric tankless. They do not last like an electric tank type or gas tankless. They pull a TON of power as well. You probably will not realize the "cost savings" before the end of life of the electric tankless. 

Basically have just seen them not last in my plumbing experience. 

I install tankless gas water heaters and have one in my own house, and it's about ten years old now.  I also have a tankless electric water heater installed in a 1/1 rental unit in Florida.  I tried it because I got a few of them in a surplus-sale packaged deal. <g>  It's only a few months in use - so I have no history to report as yet.  

Tankless water heaters, both gas and electric, all require annual maintenance unless you have perfect water.  I do have such water at my house in NJ but everywhere else that I have ever been the heat exchangers in tankless water heaters require acid flushing on an annual basis.  White vinegar in a bucket is fine - but it still has to be done.  The lack of regular maintenance is what kills the tankless units.

More than 80% of the cost of operating a water heater is the result of maintaining the tank temperature - not the actual use BTU's.  Gas fired tanks are difficult to control automatically - but electric tanks are simple:  just install a timer and you can often limit the heating to an hour per day.  As a result, I really think that a tank-type electric water heater can easily be less costly to operate - with a timer - than any other common source of water heating.

stephen

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Does your water come from a well?  Or is it from a public source?  If a public source;  is it stored in a reservoir?  Is it is stored in elevated tanks / water towers?

If from a well it would be unlikely to ever fall below about 50º F.  If from a reservoir it is unlikely to ever fall below about 40º F.  It it's stored in elevated tanks / water towers then it could easily be in the low 30's.

As you need about 110º water you will want a rise of 80º at the maximum flow rate at worst-case conditions (if that's what you have).  This is typically about 3 GPM although with low-flow shower heads you can probably get by with using 2 GPM.  

A whole-house sized unit may well require TWO 50 amp or 60 nap breakers to supply it with electricity.  

stephen
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Originally posted by @Ken P. :

Based on the several success stories related by 1BR 1BA multi unit owners above, I think I'll go ahead and install a single tankless heater, and see how it goes.  I will report the results back to the forum.  From researching this topic, one thing I know I'll need to check is the lowest incoming water temperature, so I'll probably wait until February to try to capture the lowest incoming water temp, so I can choose the correct size tankless water heat.  Thanks everyone for weighing in on this topic.

The only savings one may realize is a space savings. They are more expensive wether they are gas or electric and they still have to be maintained. Just based on personal experiences with both kinds. Just my $.02.

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