Comments on: WATER HEATER: Return on Investment (ROI) on Tankless Water Heaters

By: Go Tankless? - Gaiam Blog

Go Tankless? - Gaiam Blog — Thu, 18 Feb 2010 19:02:27 +0000

[...] GetWithGreen.com shows you how to calculate the return on your investment. [...]

By: Calculate the ROI for your own tankless water heater. : Windermere - Andrew Stone

Wed, 11 Feb 2009 17:46:30 +0000

[...] I didn’t have one until today. Over at getwithgreen.com they have just posted a very nice calculation model on tankless water heaters. I suggest that anyone considering a tankless water heater check it out. var ecov = “sh”; [...]

By: cheryl

cheryl — Thu, 05 Feb 2009 19:32:06 +0000

Dan, Yes , I gree with your comment, it seems it is the “holding cost” that would be the difference and the calculations given ccount for holding only the water used, not the 50 gal tank 24 hours per day, 365.
or 50×365x24 x the $.003 = $1314 per year for holding???
Can that be right? So that would be in favor of the tankless, but

Upon looking at the amount of water a tankless can heat I found it would take 5 $200+install units installed all over the house to have the same availability we now have.

Our house is long and the water runs for 80 feet to get to the master bath, so that amount of hot water is wasted each time we turn it on, and I thought to get a tankless for that end of the house, but found it would cost about $1000 to get what is needed for the back to back baths. I want to save energy, but that is too much $$$ for me.

By: Evan, US

Evan, US — Wed, 11 Jun 2008 18:08:38 +0000

No, Ben, you aren’t correct. Density of water changes by temperature (although by a small amount). Since water is measured in gallons(volume, not weight), and Density = Mass/Volume, if the Volume stays the same and the Density increases, the Mass increases.

It’s not like the old trick Question.

By: ben, uk

ben, uk — Mon, 09 Jun 2008 14:50:34 +0000

I cant see how a gallon of water would weigh less at different temperatures!

it s like the old trick Question, which weighs more, a pound of lead or a pound of feathers ?? its still a gallon of water either way unless you take it to the moon it won’t change weight!

By: Eric What about this?

Eric What about this? — Wed, 30 Apr 2008 20:59:21 +0000

Some more questions for Eric to think about:

Does 1 gallon of water weigh 8.34 pounds when it is 57F and 8.34 pounds at 110F? I think 1 gallon of water will weigh less as the temperature increases. What happens to your formula then?

By: Dan, Byron MN

Dan, Byron MN — Sat, 15 Mar 2008 21:28:33 +0000

I still think the numbers are bogus. The energy required to heat the water should be essentially the same in both cases — electric heat is 100% efficient. The only significant difference should be in standby losses, and, for the tank, they should be purely a function of time and temperature differential, not the amount of water used.

And somewhere it should be noted that the equations will shift significantly for gas units vs electric, since standby losses will be considerably higher.

By: WATER HEATERS: Does you wait longer for hot water when going tankless? | GetWithGreen.com

Wed, 20 Feb 2008 13:26:17 +0000

[...] The space savings will be a big draw for those of you living in smaller homes, and for some it will be the energy consumption of the tankless vs. a conventional model, or which one pays back faster? [...]

By: Pete in Milwaukee

Pete in Milwaukee — Thu, 27 Dec 2007 22:13:14 +0000

First, the calculations are incomplete. Installation can be a significant cost, particularly upgrading the gas line feed. There is also little service for tank heaters, while tankless may require more and it probably won’t be within the ability of DIYers. Water quality also affects efficiency due to scaling.

Second, I don’t believe the life expectancy claims. The short life of tank heaters is due to consumers buying low cost units. You can buy expensive ones that are long lasting. Time will tell if the more sophisticated and complex functioning of tankless will be long lasting.

By: Michael Thomas

Michael Thomas — Sun, 23 Dec 2007 16:05:57 +0000

Another variable you could consider is that if a water heater is within a conditioned space, a water heater operation is increasing a structure’s cooing cost and decreasing it’s heating cost, with the relative sized of the effects depending on the distribution of heating and cooling demand durign the year – so a tank type heater would be somewhat less efficient in FL than MN.