Indirect vs Electric Water heater

GermanPlumber

GermanPlumber

Hello to all,

I try to come up with some numbers or better I try to find out the difference in EFF betwen a 40 gall Indirect using a Weil Ultra fully condencing boiler as heat source and a 40 gall electric model. I know recovery, lifetime, etc is all better on the indirect but would like to know the difference in cost of operation. Thanks for all your help! Mario

Weezbo

i favor point of use a bit...

major thing though is they are not the same thing .recovery rates are often integral in the equation..

Brad White_113

What is your per kWH cost?

Mario-
Firstly we would need to know your relative cost of fuel be it gas or electricity. Forget efficiency for the moment for electric use is virtually 100% efficient at the point of use. (You pay for all of the inefficiency, of course!)

Secondly, do you have a projected usage? Gallons per day or per hour? Absent that, you may want to express the values as so many gallons or "per tank from a cold start".

If we take an average 40 gallon electric DHWH using two 4.5 kW elements (30.7 MBH) or a similar indirect and raise the water 90 degrees from 50 to 140 F, we have:

40 gallons x 8.34 lbs. per = 333.2 lbs. x 90 degrees = 29,988 BTU's. This holds for either tank type, hot water is hot water.

It would take 58.6 minutes, call it an hour at 9 kW input rate to make that temperature. Call the consumption 9.0 kW/hours. If your cost per kWH is say ten cents, you will spend 90 cents for that first tankful of hot water. Your local cost may vary, naturally.

Now, suppose you have a 40 gallon indirect, maybe with an output of 100 MBH and an efficiency of 90% average during DWH production.

That same tank would come to temperature in about 20 minutes and use 36.67 MBH gas input, a little over 1/3 of a therm.

If your cost per therm is, oh, $2.25, that would cost you about 82.5 cents for the same hot water, first full hot tank from a cold start. This is about 90% the cost of electric but only at the stated rates.

Plug in your local fuel numbers, boiler configuration and sizing and see what you get, Mario.

Best,

Brad

GermanPlumber

Brad and Weezbe thanks so much guys for the quick help. Mario

Robert O'Brien

It

depends on utility rates.On LI my most recent electric bill was 21.77c KWH with all fuel surcharges. That would make the gas equivalent of $6.38 per therm! Gas is about $1.90/therm here. So the answer is over 3x as much to use electricity after accounting for efficiency losses with gas.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

GermanPlumber

Brad and Weezbe thanks so much guys for the quick help. Mario

Robert O'Brien

Brad

Electricity is only 10c KWH in MA? I thought you got the same screwing we do!

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

GermanPlumber

GermanPlumber

Here some pictures of a Install I did as you can see I love Indirect,lol. Thanks again guys! mario

Weezbo

just wondering ...

is that NEC i see there?

your work looks pretty straight staight is good:)

do you have a backflow preventor in front of the fast fill?

and a hot water line and a relife drop?:) still to get back at?:)

hr

Nice install

no need to worry about operating cost on that install, no gas line connection Nice piping work.

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Perry_2

Great Question - it depends on...

your application as Brad indicated above.

However, if you did not use natural gas for heating the numbers would absolutely sway towards electric. The reason is the gas companies essentially charge a "meter" charge (typical in the US). Arround here it's about $12 per month. Now since I use $6 - $8 dollars for hot water, the actual cost per them used (or cost per gallons of hot water) is astronomical when you pay the gas bill. About 3 times the cost of the gas.

I was looking to install a geothermal system; but cannot get one that kicks out 140 F water. In that case I would have switched back to electric hot water just to get rid of gas meter charges. Paying one meter charge is sufficent.

Amazingly, the people pushing gas hot water never seem to include the monthy meter fee into their calculations.

For a normal houshold that does not need a lot of heat. Electric is actually the cheaper alternative than gas water, stove, cloths dryer when you consider all the cost involved.

For a small heating load - electric agains wins out on the low install and maintenance cost.

Perry

GermanPlumber

Hot Rod and Weezbo yes my job was not finished when I took the pictures,lol. This was the last job where I solderd pipes. I finaly bought the Ridgid Pro-Press system. I used the same system in Germany for so many years and was happy I could pay for the press here. I will post some pictures soon. I am once again feel goodto have this connection here to get some feedback and answers thanks to all of you! Mario

Brad White_9

Oh, we get screwed all right, Robert...

I just used ten cents because it makes the math easier!

We are probably in the range of 13 cents and depending on your structure even some residences are getting demand charges (in exchange for a "better" base rate.

Brad White_9

You win.

Yup, you are getting reamed sideways, Robert. But to be fair, the traditional breakdown of electrical energy to fossil fuel has been about 3:1. Lately with the spikes in fossil fuel it has dipped to 2:1 and seems to have been corrected in your case. I will probably have to re-examine my actual total cost of electricity in light of my 13 cent projection.