turbo,
I greatly respect your engineering expertise, but I think you're mistaken on the question of gas vs electric 'gallon recover rate @ 90 degree rise', and operating $ cost, although you may be right with LPG costs, I don't know.
However, a NG water heater will about double the hourly output, if not greater, than an equally sized electric unit... and for about 1/2 the cost or less, depending on the local utility costs and the unit efficiencies.
Example:
The NG water heater I've got is the AO Smith Vertex Power Vent GHPE 50 gallon unit. It used to cost about $1200 and is now priced, absurdly, up around $2200+ (I'd tell anyone to walk away fast even at half the price).
The specs on the 50 gallon unit are:
AOSmith Vertex Specs.png
There is no way the average, or even a premium, residential electric heater can match a
120+ gallon first hour and a 90+ gallon second hour and beyond recovery rate. We can run two showers, the clothes washer on hot loads and the dish washer all at the same time all day long. Obviously, we don't do that or need to with just the two of us. I installed the unit at the time because I thought we might move and thus sized it for a full house of kids, etc.
As for the operating costs, based on our
actual numbers from Ft. Hill Gas and Duke Energy,
the NG costs are right about 1/3 the cost of the electric...
- 1 Therm = 100,000 BTU
- $0.95831 per Therm
=
$0.95831 / 100,000 BTU
100,000 BTU = 29.29 KW
- $0.0984 per KW
=
$2.88 / 100,000 BTU
Please feel free to show me where any of my numbers are wrong in case I've moved a decimal point or something.
As for why my units are crapping out... I spent a month or more working with AO's tech people back in 2016 when I first had problems with the ignitor/flame sensor refusing to light off. I had the gas company test and change out their gas regulator (even though the old one was in the middle of the spec @ .075 psi ~ 2" water column). I subsequently installed a new Intellivent control unit on the water heater and set the gas manifold pressure at the nominal 2" water column pressure, but actually had to cut back the inlet gas valve to accomplish it.
AOS techs reviewed a video of the burner flame and 'blessed it' as being acceptable. Thus, I'm haven't been 'cooking' the unit as far as they or I can tell.
The inlet cold water is regulated down from line pressure to 30 psi before it goes through an expansion tank and then into the water heater. I've also regulated down the cold water pressure into the MB shower to 50 psi so as to allow the Moen pressure balancing valve to work effectively. If we were seeing hot water temperature fluctuations due to the dip tube dumping cold water, higher inlet cold water pressure (as one AO Rep claimed was the problem the other day), or a thermostat problem, we'd see it in the shower temperature control valve and that nominal positioning hasn't changed over the years except when I increased the hot water temp from 125 deg to 130 deg awhile back.
I'd love to figure out why these units are failing (leaking through the sidewalls) within 5-6 years. If there's something wrong with our water or the setup that I've missed, I need to ID it before I install a new heater in the near future.
Btw, the last time I checked, our incoming water PH was just about 7.0 or tad higher (I think). I need to recheck that to be sure.
Any other ideas?
I did read awhile back about a company that was coming out with a residential water heater with a 'plastic' lining vs the glass, but need to see if they're still on the market and what the feedback is. I don't know if that's a good idea or not, but something has to be better than these glass-lined tanks that get cracks in them in a few years.
And, no, I have no interest in a tankless unit for all the reasons you explained above.
Thanks.
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