Metering Domestic Hot Water Usage

Yeah I know... I'm a little over the top sometimes. But how much fun will it be to know somewhat precisely how much coal is being used for DHW? I've had this meter for a while, I finally installed it like 5 minutes ago. I used the bread plugs again to keep my copper joints dry for sweating. First attempt pressuring the lines had zero leaks

I have a digital thermometer after the mixing valve that stays really close to 125 degrees while hot water is running. So we'll figure a 75 degree rise using 10,000 BTU per pound of coal to factor in efficiency. We can even compare it to electricity at 16 cents per kilowatt for even more fun!

Who else meters DHW?
What's your average gallons per day?

Over the past 3 years we’ve averaged 42 gallons per day.

hotblast1357 wrote: ↑

Wed. Nov. 24, 2021 6:03 am

Over the past 3 years we’ve averaged 42 gallons per day.

I would say that's a pretty steady average since over 3 years! How many in the household, if you don't mind me askin?

Water have different weights at different temperatures. According to this calculator, water weighs 8.251 pounds at 120 degrees Fahrenheit, since we're metering the hot side. So I'll use that figure for calculating BTUs.

https://www.thecalculatorsite.com/conversions/com ... weight.php

The British thermal unit is a unit of heat; it is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. It is also part of the United States customary units. Heat is now known to be equivalent to energy.

So for 1 gallon of water to raise 75 degrees
8.251 pounds x 75 degrees = 618.825 BTUs per gallon

So, if I did all that right, we have all our constants for measuring the coal consumption..

hotblast1357 wrote: ↑

Wed. Nov. 24, 2021 6:03 am

Over the past 3 years we’ve averaged 42 gallons per day.

42 gallons x 618.825 BTUs = 25,990.65 BTUs ÷ 10000 = about 2.6 pounds of coal per day.. is that right?

Are you trying to bring Larry out of retirement ?

tsb wrote: ↑

Wed. Nov. 24, 2021 9:30 am

Are you trying to bring Larry out of retirement ?

Sure! Bring him on!
I need somebody to check my math

tsb wrote: ↑

Wed. Nov. 24, 2021 9:30 am

Are you trying to bring Larry out of retirement ?

I had the same thought - he would love this.

My coal costs $235 per ton which is 11.75 cents per pound.. Now we can figure cost..

And at 16 cents per kilowatt we have 1 kWh producing 3412.14 BTU.. now we can compare it to electric..

Rob R. wrote: ↑

Wed. Nov. 24, 2021 9:43 am

I had the same thought - he would love this.

I know right?
I miss Larry

What? No bread for toast?? Sorry honey, I used the last couple slices for bread plugs while plumbing yesterday.. yer one of kind, she says.. but she doesn't understand the struggle

It's a sad day when the breadman doesn't have any bread in the house..

OooOOoooo.... I was wrong about the cost of my electric. My most recent bill total divided by kilowatts is 19.2 cents per kilowatt.. Game changer!

Lightning wrote: ↑

Wed. Nov. 24, 2021 10:44 am

OooOOoooo.... I was wrong about the cost of my electric. My most recent bill total divided by kilowatts is 19.2 cents per kilowatt.. Game changer!

The less you use the higher the rate.

So.. cost per gallon to heat water with coal is $0.0072711938

Cost per gallon to heat water with electric is $0.0348210971

Electric is more expensive to heat water with than coal by a factor of 4.8 times!!

I need some peer review here lol, is that figure right? Seems legit to me.

Rob R. wrote: ↑

Wed. Nov. 24, 2021 10:54 am

The less you use the higher the rate.

That was based on 929 kilowatts used for the month, which is pretty close to normal usage thru the winter months.

We're at 38 gallons of hot water today and we're just getting started lol

Lightning wrote: ↑

Wed. Nov. 24, 2021 11:05 am

We're at 38 gallons of hot water today and we're just getting started lol

I think you will find that your DHW usage on some days is far higher than others. We tend to use a lot more on the weekends.