Problem with economics of on demand hot water heaters

[Roger Johnson]

A friend who was contemplating replacing his always on gas fired 50 gallon hot water heater setup with an on demand system told me there's no economics in it after he ran a long term test (for months).

He gauged his propane use by his monthly fillup gallonage during the summer months where the outside temperature was relatively steady and warm (so the tank fills were all to about 80 percent).

He didn't see ANY difference in propane use between these two scenarios. Control: 50 gallon hot water heater left always on Testing: He turns on the hot water heater each morning for an hour

Since it's just him, his wife, and one other adult, they can all take showers in the morning on that schedule.

Given that a new on demand system could cost as much as five grand, would you agree with him that on-demand systems have no economic value?

[Clare Snyder]

Been saying that for years - they will never last long enough to pay foe themselves

[Ed Pawlowski]

Correct. Just look at the initial cost and do some rough numbers. How many showers and dishwasher loads for payback?

The only real difference is the cost of standby on a tank heater. New tanks are better insulated so that is minimized. Better yet is the indirect fired tanks, again, well insulated. My burner never goes on just to heat in standby, only if hot water is used. I know someone that has the same setup as mine, went away for a week and turned the boiler off. They came home and on the second shower realized it was never turned back on.

[Terry Coombs]

  What's your take on point of use heaters ? Ours is a small one , only about 1.5 gallons , mounted in the crawl space under the kitchen sink area . The reason we got it was because hot water took too long to get from the main heater (40 gal electric) to the dishwasher/sink . Additionally , the main is set at 130° or so and we wanted minimum 140° at the dishwasher . Never got over 120° coming from the main to the D/W and that ain't hot enough to sanitize the dishes .

[trader_4]

There has been many posts here over the years, a lot of analysis and every time I've seen, it's the same conclusion. In most cases an on demand water heater makes no sense because you'll never recover the increased cost. The standby losses from a tank type are not that significant, the savings would take a very long time to make up the additional upfront cost.

And the upfront cost in going from a tank to a tankless can be large, including possibly resizing the gas supply lines all the way to the meter. They can make sense for special applications, like a beach rental property, where you want unlimited hot water at peak times, it won't be on at all during periods it;s unoccupied, etc. If it's put in during new construction, that can help too, as it's less money to just run a larger gas service instead of replacing what's there.

[Ed Pawlowski]

I don't see much difference in cost wither way. The small tanks are often not as well insulated but if the distance to the regular tank is long, it will save water as the hot will be there quickly.

As for the dishwasher, I get excellent results with 120 degree water as there is a sani portion in the cycle that raises the temperature. Coupled with the caustic detergent, they should be sanitized well. It also helps to use a good detergent. We use Cascade Platinum and also a rinse aid.

[dpb]

The above doesn't incorporate any savings in water usage but unless in one of those areas with extremely high rates coupled with sewage rates based on usage and a high water use still very unlikely to actually be an economic benefit.

It's the reason most eco-friendly things don't win on their own in the marketplace; while they may have side benefits, on economics alone they simply don't pay.

[Terry Coombs]

She buys the cheap stuff ... but we do use a rinse aid . I do like having the very hot water at the sink too for those few items that we hand wash . last rinse is straight hot .

[Ed Pawlowski]

Splurge once and get the Platinum. I gave away the jug of regular stuff I had when I saw the difference.

[Terry Coombs]

  She does the shopping ... I can hang the request on the fact that sometimes my coffee cups don't come clean .

[gfretwell]

I thought dish washers turned on the drying element to raise the temperature of the water to a sanitizing level, no matter how cold it was going in. I know there is a pretty good blast of steam coming out if you shut it down right at the end of the wash cycle and open the door. I don't have a dish washer here but there is always one in the houses we rent on vacation.

[Clare Snyder]

Excellent solution. Point of use on demands work good for some things too (they hold a quart or so of steeming hot water and draw about 1500 watts - like an "on demand tea kettle"

[Terry Coombs]

  Did you miss the part where I said "ours is a small one , only about 1.5 gallons" ?

[makolber]

yes I agree.

Especially if you live in a cold climate, the "waste" heat is not really wasted but helps heat the living space.

m

[Clare Snyder]

Nope - didn't miss it. That's "medium sized" for a POU. 5 is typically the largest.

[trader_4]

I believe that is correct. I know on mine, it stops sometimes in at least one of the cycels, pausing for a few minutes, which I presume is while the water is being heated. They have the heater element down in the water, it would be kind of stupid to not use it to heat water that isn't hot enough. The exception there would be in the govt has some energy efficienc y standards they have to meet and if they let the thing run with cold water they meet it, but heating it would not.