Why Tankless, Hybrid Electric, and Solar Water Heaters Just Don't Work!

Tankless- expensive, high maintenance, high failure rates, high install costs, limited flow rates, poor winter performance, long payback.

Hybrid Electric- too tall, need surrounding space for heat exchange, poor durability, noisy, may need condensate pump.

Solar- requires southern exposure, cold & cloudy days: poor performance, very long payback, high install costs

What works?

The good old Storage Tank water heater- electric is OK, fast payback for gas or propane fueled(if low fuel price). Easy to maintain. Best to purchase long warranty unit for maximum durability.

How can this be? The best available technology at a reasonable cost will always prevail. And it has to, in a word, JUST WORK! With the exception, sometimes, of federal government mandated technology, (and dehumidifiers)!

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Comment by Curt Kinder on December 20, 2012 at 7:32pm

There are so many variables affecting the typical residential electricity bill that I've grown to be highly skeptical of claims linking actions with cost.

Before accepting claimed savings I would require data in the form of either sub-metering the water heater circuit or connecting hour meters across both elements.

Comment by Bob Waldrop on December 20, 2012 at 6:57pm

Curt, thanks for the verification on the ability to get hot water fairly quickly.  Your comments are similar to something we were told locally when we called the electrician who installed the hot water heater and asked him how it was possible that we could get hot water so quickly. 

We do not use the circuit breaker to turn the water heater off and on. When it was installed, we got a permit from the City, the electrician installed an on and off switch and the installation was inspected by Oklahoma City electric inspectors. We didn't know what you said about circuit breakers, but our breakers are outside and we figured we were more likely to flip the switch if it were indoors.

We have experimented with leaving the heater on 24/7, but it seems to us that our electric bill goes up when we do that.

Comment by Curt Kinder on December 20, 2012 at 6:30pm

I don't share the skepticism of short cycling a storage electric water heater. I've measured temperature drops of 1 degree every 4 hours during de-energized periods. That means a tank set at 120 would deliver 108 after 2 days. (120-(48/4)

Restarting the heater energizes the upper element until its thermostat is satisfied, and then the lower element is allowed to fire. The upper element on a 50 gallon heater is only working on '10-15 gallons of water, so the math actually pencils out as follows:

4500 Watt element emits more than 15,000 BTUH. If it is working on 12.5 gallons of water in the top quarter of the tank, consider that 12.5 gallons is about 100 lbs, so 15,000 btuh warms that mass of water 2.5 degrees per minute, so about 5 minutes after element starts, the 108 degree 100 LB volume of water warms to 120, the upper element thermostat opens and the lower element goes to work on the rest of the tank. The 12.5 gallons of 120*F water easily supports a quick shower, and the rest of the tank is fully warmed by the end of the two hour on-cycle.

It is worth noting that operating a water heater in this fashion really saves very little, owing to the very same low standby loss described above. Standby loss is linearly related to delta T between tank contents and ambient air temperature, and the 2 on 46 off operating schedule results in fairly small delta-T difference compared with constant-on operation.

Stated another way, storage electric water heaters operated conventionally (always on) lose just 5-10% of their total electricity consumption to standby loss. The 2 on 46 off schedule likely cuts the loss from 5-10%, to 4-8%, saving perhaps a dollar per month...is that worthwhile.

Finally, I suspect the 2 on 46 off operation is effected by manually switching the water heater's circuit breaker off. Circuit breakers are NOT designed and should not be used as manual control switches. Such usage degrades their primary purpose as overcurrent protection devices, increasing risk they won't trip when needed

If you absolutely insist on regularly cycling power to the water heater, invest $20 in a junction box and heavy duty 2 pole manual switch rated for 30 amps at 240Vac

Comment by Bob Waldrop on December 20, 2012 at 6:09pm

I am not sure why you think I would put the solar water heater inside my solar sunporch.  The purpose of the 120 sq ft of glazing on the south side of the house is to heat the house, not to heat the water.  Any sunlight diverted towards heating water is not available for heating the house.  The solar hot water heater will go on the roof.  I should explain that I am 60 years old and plan on retiring in 7 yeara.  Since I have not made a huge amount of money in my life, I will definitely be on a restricted budget during retirement. I sometimes say my retirement plan is a house with no debt, that is extremely cheap to operate, and which has lots of edible landscaping.  So I am spending money now, while I have income, so I don't have to spend money later. 

I suppose we are frugal with hot water. We have four people in the house, one shower, fitted with a low flow showerhead (IIRC 1.5 gal/min). We take short showers (5 minutes or less ). We don't have a washing machine or dishwasher, we wash dishes once a day by hand in the sink, but we only use hot water to wash, we rinse in cold water. The temp on the tank is set hot.  We have a 50 gallon hot water heater.   Electric hot water heaters are better insulated than gas heaters but we also wrapped it in an insulating blanket. We don't intend to replace the electric water heater tank with the solar hot water, it will act as the back-up and inhouse tank. When the sun is shining, we won't have to flip the switch on the electric heater at all. That's probably 2/3rds of the days of the year or more around here, given the way our drought cycle seems to be developing.

Comment by Curt Kinder on December 20, 2012 at 5:40pm

Surely you jest! Is this satire?

Operating a propane-fired center flue storage tank water heater operating at 50-60% efficiency and a fuel cost of $3.50 or more per gallon is utter lunacy, barking mad in all but the coldest, highest electricity cost regions.

A heat pump water heater installed in a Florida garage operates at 3x the efficiency of any electric resistance water heater, tank or tankless. Payback is 3-6 years, and useful cooling and dehumidification results.

Natural gas fired tankless units may make sense wherever NG is available, so long as water is naturally or artificially soft.

A storage electric resistance water heater is a reasonable solution for a single person household. OTOH solar thermal starts to make sense for extremely large families, 7+ people, if good solar conditions obtain.

My point is that there is no one correct answer for heating water, other than to acknowledge that water heating is often the second largest domestic energy consumer; exceeded only by heating / cooling. Every individual situation and region varies, and the best alternative percolates to the top only after considering conditions specific to the application.

Comment by Bob Blanchette on December 20, 2012 at 4:36pm

No way any water heater will give hot water in 10 minutes with a cold start. It takes at least 30 minutes for an electric water heater to produce any hot water, longer in winter when entering water temperatures are colder.

As far as the gas water heater/fan coil setup the idea is you get two 90%+ products for the price of one.

Comment by Tom Delconte on December 20, 2012 at 3:16pm

Hello Bob,

Please feel free to join in the conversation in the Forum and Groups! OK, let me figure your home setup, out, without being cutting or snide.

First, how in heaven's name can you run an electric hot water heater on a manual duty cycle of 2 out of 48 hours? This is an achievement that goes beyond all human reckoning! Chris Laumer-Giddens once complimented me on being able to use only 25 gal of water per person in our home, but you get max kudos for using the least Hot Water that anyone in the USA!

Good luck with the high installation cost and long payback of solar hot water, which from your description you intend to mount the collectors Inside the windows of your wall. Great luck with that! And it should look mighty attractive. Oh- the thing about water heaters that any plumber will tell you- if it ain't broke and leaking, don't replace it!

You have completely lost me when you make accusations in your first and last sentences. what did your mother teach you? I'm not against all federal mandated tech. I'm not against anything. What I said was the Truth- some of it works, and some of it doesn't. That's the Plain Truth, not ascribing to some political stance, or idea system.

Could this be the start of the Revolution, right here in this little old blog? Hardly! Look at the home-energy-pros map: most of the members are back east. The costs are greater here. Any discussion of autos, please refer to my auto blog!

Comment by Bob Waldrop on December 20, 2012 at 12:03pm

This sounds more like an ideological statement than anything else.  We use an electric waterheater, but we installed an on-off switch, and we turn it on when we need hot water and it has cooled down.  When it has cooled to ambient, when we flip the switch, within about 10 minutes we get a stream of hot water from the hot water taps or the shower. Generally, we turn it on for a couple of hours every other day. When we put it in, we couldn't afford the other options you mention, but when we get a few more shekels we intend to install solar, keeping our present tank as backup.  We're in Oklahoma, and have great southern exposure.  We get a lot of our winter heat from the 120 sq ft of windows we installed on our south wall.  I am wondering if your distaste for government mandated technology also extends to the automobile, which is heavily subsidized by general tax revenues, bond issues, and other non-automotive-related revenue sources.

Comment by Tom Delconte on December 20, 2012 at 10:09am

Hello William,

Thanks for your remark! I believe what you meant to say was that your annual space heating( I guess, since the usual old setup used to be oil boiler with summer water hookup) + water heating + electric were $3,000 the first year, 19xx, or 20xx, that you looked at them and added them together. As of Nov. 2012, your annual electric bill is now $870, not declaring killowatthours in the above.

Your propane bill is now $85 per year for hot water, which would be about 28 gallons of propane at $3 per gallon, which is completely amazing! Of course, most house setups use propane for fireplace, range, dryer, sometimes central heat, once the tank is installed. I do not enjoy the luxury of having a separate small propane meter on each appliance, as you must have. You are truly an ideal home energy saver! Please remember to do the maintenance on your tankless water heater!

Ahh, yes the source of my data. It's called The Real World. I hated it when MTV appropriated my 'patented' phrase!

Comment by William H Nickerson on December 20, 2012 at 9:10am

Tom, I drove to Baltimore to pay $350.00 for a sealed combustion propane tankless and put it in myself. My annual combined bills [oil boiler and electric ] were at $3,000.00 my first yr. of counting. Last month my ann. electric. now is $870. and the propane is less than $85 per yr. for all hot water. You should really put your hands on some of this work as compared to reading someone else's findings.

 

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