Consumer Homes.

Question:

We have been doing some more calculations and find that for a typical home with 1/2 inch pipe running 30 feet from the storage water heater to the point of use, the amount of water which sits in the pipe is .3 gallons and weighs about 2.4 pounds. Some people have emailed me about wasted water being a concern, I’d like to know if this amounts to more than 1% for any household. (engineers usually don’t care about things much less than 10%). I figure .3 gallons twice a day every day is 18 gallons/month.  Is there anyone that uses less than 1800 gallons/month?  We are pretty good at conserving and use something like 10,000 gallons per month. As for energy cost, 2.4 pounds times 70 degrees F = 168 BTUs.  Twice a day every day of the month is 10,080 BTUs or 1 tenth of a therm. A nickel for me. — My opinions are my own. Happy owner of a new Mitsubishi Expo.

Response:

|>  <<text deleted>> |> >So I am paying about fifty cents per month for my water heater’s |> >standing losses. It would be nice to avoid that, but I don’t see it as |> >a high priority. |> |> Without actually doing any fancy calculations, I know my tankless heater |> dropped my summer monthly gas bill has dropped from about $50 a month |> to about $25 even though we also installed a gas stove AND even |> though I no longer turn off the furnace pilot in the summer because |> it is now in the attic. |> |> John For another datapoint, my summer monthly gas bill is $5 to $8, with a relatively new standard water heater (has insulation in it, so I put none around it).  The gas stove probably draws relatively little. There are clearly instances where one or the other kind of heater is preferable, and some where the difference is ambiguous. Bruce Nordman

Response:

>>I figure .3 gallons twice a day every day is 18 gallons/month.  Is there >anyone that uses less than 1800 gallons/month?  We are pretty good at >conserving and use something like 10,000 gallons per month. >My household (both of them actually) uses about 1100 (one thousand, >one hundred) gallons per month average.  Two people.  We don’t take >*any* water conservation measures except sharing the shower .

That’s pretty amazing. That’s about 1.5 units (100 CF). You live in an apartment, I assume. >If you use 10k gallons a month and have less than 10 people in your >household, then you are *not* conserving.  

Come on, that’s only .03 acre-feet…. — My opinions are my own. Happy owner of a new Mitsubishi Expo.

Response:

>>>I figure .3 gallons twice a day every day is 18 gallons/month.  Is there >>anyone that uses less than 1800 gallons/month?  We are pretty good at >>conserving and use something like 10,000 gallons per month. >My household (both of them actually) uses about 1100 (one thousand, >one hundred) gallons per month average.  Two people.  We don’t take >*any* water conservation measures except sharing the shower . >That’s pretty amazing. That’s about 1.5 units (100 CF). You live in >an apartment, I assume.

Our utility sells it by the kilogallon.  No, I live in a full size house with my SO, 2 cats, and all our caving gear.  I have about 25000sqf of lawn that grows more than enough even without watering, and have 2 vehicles that get washed on occasion.  My neighbor, with 4 people in her household uses less than 3k gal. I have both a bath, and a shower, and a standard tanked flush toilet. The worse I ever did was once when I went away for a weekend and left the hose on full I used about 8k gal. that month. >If you use 10k gallons a month and have less than 10 people in your >household, then you are *not* conserving.   >Come on, that’s only .03 acre-feet….

I’m talking about a *household*, not a farm, as I presume you were as well.  If you are talking about a farm, the 10k gal is a very low figure. — Anmar Mirza   # Mayor of Dogspit, IN  #My Opinions! NotIU’s! #Purveyor of EMT-D         # Located somewhere in  # Legalize Explosives! #nontraditional N9ISY (tech)  # the Outback of the    #I’ve got my own fusion#family values Networks Tech.# Mirza Ranch.C’mon over#plant. Just ask me.   #Space For Rent

Response:

PN>>If you use 10k gallons a month and have less than 10 people in your PN>>household, then you are *not* conserving. PN>Come on, that’s only .03 acre-feet…. Just goes to show that one man’s flood is another man’s drought. hhs —  . SLMR 2.1a . Backup not found: (A)bort (R)etry (P)anic

Response:

>We have been doing some more calculations and find that for a typical >home with 1/2 inch pipe running 30 feet from the storage water heater >to the point of use, the amount of water which sits in the pipe is .3 >gallons and weighs about 2.4 pounds. Some people have emailed me about >wasted water being a concern, I’d like to know if this amounts to more >than 1% for any household. (engineers usually don’t care about things >much less than 10%). >I figure .3 gallons twice a day every day is 18 gallons/month.  Is there >anyone that uses less than 1800 gallons/month?  We are pretty good at >conserving and use something like 10,000 gallons per month.

My household (both of them actually) uses about 1100 (one thousand, one hundred) gallons per month average.  Two people.  We don’t take *any* water conservation measures except sharing the shower . If you use 10k gallons a month and have less than 10 people in your household, then you are *not* conserving.   Around here, in the city our sewer is charged by how much water we use (in the summer sewer is charged by an average of March/April water usage), and at 10k gal. per month we’d have about a $90 water bill. — Anmar Mirza   # Mayor of Dogspit, IN  #My Opinions! NotIU’s! #Purveyor of EMT-D         # Located somewhere in  # Legalize Explosives! #nontraditional N9ISY (tech)  # the Outback of the    #I’ve got my own fusion#family values Networks Tech.# Mirza Ranch.C’mon over#plant. Just ask me.   #Space For Rent

Response:

>My water heater is 55 inches high with an external circumference of 56 >inches.  Use the external circumference as a worse case assumption, the >area is 55 * 56 = 3080 square inches or 21.4 square feet. Assume the >heater wall has an R-8 value insulation and the temperature difference >is 120F-70F = 50 F. >So I am paying about fifty cents per month for my water heater’s >standing losses. It would be nice to avoid that, but I don’t see it as >a high priority.

You have, of course, overlooked the major heat loss paths.  They are heat lost up the flue and heat lost through the piping.  The former is very significant because it is driven by the very heat that is being lost.  Notice how your flue remains warm all the time.  Most people attribute it to pilot heat but it remains even when the pilot is turned off.  The latter is also significant because there is convection flow in the pipe.  There are convection breakers available but almost no one installs them. Without actually doing any fancy calculations, I know my tankless heater dropped my summer monthly gas bill has dropped from about $50 a month to about $25 even though we also installed a gas stove AND even though I no longer turn off the furnace pilot in the summer because it is now in the attic. John — John De Armond, WD4OQC               |Interested in high performance mobility?   Performance Engineering Magazine (TM) | Marietta, Ga                         |Interested in high tech and computers? Need Usenet public Access in Atlanta?  Write Me for info on Dixie.com.

Response:

>Wouldn’t you also have to consider the losses from the pipes between the heater >and the point of use?  I takes a couple of minutes for the hot water to reach my >shower, and there are probably lots of therms left in the pipes when I turn the >water off.  These losses would reduce the payback period for the in-line heater.

First of all, I am positive there are not "lots of therms left in the pipes". A therm is 100,000 BTUs and if you had that many BTUs in your pipes, they’d be steam pipes. You’re assuming you mount the water heater(S) right next to point of use. How much are these heaters? I’ve seen them go for $400. One for each bathroom, kitchen, and laundry? Are you going to run a new gas line to each of these devices? Why don’t you catch the cold water that comes out while waiting for hot water and tell me how many gallons it takes. We can then multiply 8 pounds per gallon times the temperature rise (maybe 60 F?) to get the number of BTUs "wasted". 4 gallons would be about 2000 btus, or one penny worth of heat at 50 cents per therm. — My opinions are my own. Happy owner of a new Mitsubishi Expo.

Response:

- Hide quoted text — Show quoted text -> These systems >cost more than our American tank heaters, but they are far more energy efficent > and will pay for themselves in two years. >They certainly do cost more. As for how much more efficient they are, the >numbers I ran look like this: >My water heater is 55 inches high with an external circumference of 56 >inches.  Use the external circumference as a worse case assumption, the >area is 55 * 56 = 3080 square inches or 21.4 square feet. Assume the >heater wall has an R-8 value insulation and the temperature difference >is 120F-70F = 50 F. >This results in a loss of 134 BTUs per hour, or .98 therms/month. >So I am paying about fifty cents per month for my water heater’s >standing losses. It would be nice to avoid that, but I don’t see it as >a high priority. >– >My opinions are my own. >Happy owner of a new Mitsubishi Expo.

Wouldn’t you also have to consider the losses from the pipes between the heater and the point of use?  I takes a couple of minutes for the hot water to reach my shower, and there are probably lots of therms left in the pipes when I turn the water off.  These losses would reduce the payback period for the in-line heater. —

Response:

> These systems >cost more than our American tank heaters, but they are far more energy efficent > and will pay for themselves in two years.

They certainly do cost more. As for how much more efficient they are, the numbers I ran look like this: My water heater is 55 inches high with an external circumference of 56 inches.  Use the external circumference as a worse case assumption, the area is 55 * 56 = 3080 square inches or 21.4 square feet. Assume the heater wall has an R-8 value insulation and the temperature difference is 120F-70F = 50 F. This results in a loss of 134 BTUs per hour, or .98 therms/month. So I am paying about fifty cents per month for my water heater’s standing losses. It would be nice to avoid that, but I don’t see it as a high priority. — My opinions are my own. Happy owner of a new Mitsubishi Expo.

Response: