Are Tankless Water Heaters a Waste of Money?

[Norm A. Brams]

Basically they save floor space and deliver an endless supply of hot water...until they break.

Will they save you money? No!

[Steve Barker]

that's no secret. They don't deliver 140+ degree water either. ESPECIALLY when the incoming is 38 degrees.

[RonB]

Our son put a Bosch tankless heater in his home when they built it almost 5 years ago. He is rural and uses propane and he is more than convinced it is saving him a lot energy money.

But it ain't all good. In the past few months the holding tank sprung a leak (not the tankless heaters fault), then a valve problem. About two weeks ago it started leaking a little and he called a plumber friend. The plumber told him on the phone it was likely an O-Ring that he could fix himself but Scott was too busy to work on it and told the plumber to come on out. Good thing because the heat exchanger had sprung and serious leak and they had to replace the entire heater. Fortunately he was about two months inside of his warrant period and he got a new heater with a new warranty for cost of labor. He says he would probably put one in again but he isn't quite as sold on them.

Another thing we noticed when we visited was noise. He has it in a long closet next to the guest bedroom and when that thing comes on it is LOUD.

RonB

[Home Guy]

Facts:

1) Natural gas prices have been very low the past few years, and there's no indication that's going to change in the next few years. Anything you spend to reduce natural gas usage will have a proportionately small return on investment given low gas prices. 2) Conventional hot-water tanks are pretty efficient from a standing-loss standpoint, and what little heat they do radiate can be reduced by a relatively cheap external insulation blanket. On the other hand, the radiant heat loss from the tank is captured inside your house, the advantage of which is proportional to your northern geographic location (or as a function of altitude). 3) heat loss from a conventional tank flue is minimal if you have a power-vented system (when the fan isin't turning, it's acting like a baffle preventing air flow through the flue). I suppose a power-operated shutter could be added to completely close the flue and prevent heat loss when the burner is not on. 4) efficiency of heat transfer is inversely proportional to the heat gradient. The burner of an on-demand heater needs to put out 10's of thousands, even 100+ thousand BTU in order to heat incoming water during the water's short residency time inside the heater for the water to reach conventional hot-water temperature (typically 140 to 160 f). The more north you are, the colder your incoming water supply will be, and the more capacity (in BTU) the burners will need to be to bring the water up to the desired temperature. Exhaust heat loss from these units is significant while they are operating, and during their off-cycle as they cool down they can't dump much heat energy into the water because there isin't much water stored in the unit.

Conversely, the burner of a conventional water tank is capable of much less BTU heating, and the heat from the burner has more time to come into contact with the internal tank surface and transfer it's heat into the water. The exhaust gas temperature in the flue of a conventional heater can be so cool as to require a small electric blower to properly exhaust the gas out the flue. This is an indication that most of the combustion heat is being transfered into the water and not being exhausted out the chimney.

In other words, perhaps 50% of the combustion heat of an on-demand heater is actually being transfered to the incoming cold water and the other 50% is being lost in the exhaust, while 80% of the combustion heat is absorbed by the water in a conventional tank. The difference is that an on-demand heater is on perhaps 30 to 90 minutes per day, while a conventional tank might be on for 4 hours a day. But remember that when a conventional tank is on, it's burners are using a much smaller amount of gas compared to the on-demand heater.

5) the efficient use of an on-demand heater is challenged by short hot-water usage events. In most houses, the hot water lines are minimally insulated and thus the water in them quickly drops to room temperature. Anyone turning on a hot-water tap in an upstairs bathroom will notice it take 10 to 30 seconds to actually get hot water. It doesn't matter what type of heater you have (assuming the heater is in the basement). A short hot-water use event (say, washing your hands) will end up dumping a lot of waste heat out the exhaust when an on-demand heater is signalled to turn on and then soon after turned off to heat the water for that short-use event. 6) because of the very high heating capability (BTU capacity) of on-demand heaters, the extreme thermal cycling of their internal components will age the unit much faster than a conventional water heater, and they do or will require more maintainence and repair vs a conventional water heater (they have control devices, electronics, etc, that are not present in conventional heaters, and as we all know - electronics and HVAC equipment really don't tend to co-exist very well for the long term). 7) on-demand heaters have electrical or electronic controls that require a source of AC current. Thus they will not function during a power failure. Anyone living in a northern climate that is subject to sporadic winter power failures will not appreciate the lack of hot water during extended outages.

Conclusion:

No home owner that has a working conventional gas water heater will ever live long enough to recoup the savings from replacing his existing working heater with an on-demand unit - and it's not a given that there will actually be any measureable savings in gas use.

What has been observed is that the behavior of occupants change in terms of how they use hot water when a conventional heater is replaced with an on-demand heater, and that change usually results in less hot water use (shorter showers, changes in shower heads, installation of low-flush toilets, etc, insulating hot-water supply lines inside the house) so it's not always clear where the savings come from and why.

Replacing an old / leaking conventional water heater is very easy for most novice home owners / handymen, and at a cost of only a few hundred dollars, the cost/reward ratio is still heavily in favor of replacing a old conventional water heater with a new conventional unit.

Tankless units have a crazy amount of BTU capacity. It has to, because it doesn't have much internal water capacity so it doesn't have much time to heat incoming water before it leaves the unit on it's way to your shower. You often need to supply a larger gas pipe to the unit - larger than even your furnace needs.

Combine that with all sorts of electronic burner and combustion controls and sensors, ignitors, computer controller, etc, and you've got a pile of electronics and wires that have $$$ written all over them.

I don't know why anyone would want a friggin blast furnace in their home just to heat water, when a conventional tank is so cheap and reliable.

Anyone who can't afford a few hundred bucks to buy a conventional gas water heater instead of paying $200 - $300 a year to rent it is crazy.

You will get more bang-for-the-buck by

1) putting an insulating blanket around your existing or new conventional water heater 2) insulating as much of the hot water supply lines inside your house as you can reach 3) use a low-flow shower head

On-demand water heaters are basically a crock of shit designed to give plumbing and HVAC companies a very lucrative new revenue stream.

[Steve Barker]

AMEN! and very well written. I'm gonna save this text and plagiarize it as needed.

[gonjah]

It was cut and pasted from another ng.

You didn't really think HG wrote this did you?

LOL

[Home Guy]

gonjah used improper usenet message composition style by unnecessarily full-quoting:

The joke's on you.

Check the full headers.

[Steve Barker]

>>>

don't care where it came from. it was correct information.

[Attila.Iskander]

1) The cost numbers are pretty high 2) There was also a recent price drop of nearly 50% for tankless heaters. 3) Regular chimney vented tankless are no different to install than tank heaters and are an easy DIY 2) If you're going from a chimney vented tank to a condensing tankless, them you have the added cost of the intake and exhaust pipes, which should be of equal length. Also doable as a DIY

Notice also that the tankless, albeit not showing a measured efficiency near it's rating, still rated higher than a tank heater.

I had a 40 gallon chimney vented tank heater feeding the whole house. I added a condensing type equivalent tankless, for $500. feeds directly the kitchen and basement laundry room, and bath and shower that are under the kitchen. Then tank heater feeds the 1st floor WC & sink and the upstairs bathroom with tub & shower. which are vertically above it. The tankless also feeds the water heater when demand from the heater has gone past 20 gallons. No more running out of hot water upstairs....

Total Natgas consumption is down. When the hot water tank goes, it will be replaced with a tankless too.

[clare]

>

Using a 5 gallon "point of use" tank will give you ALL of the upside, without the downside. Use the big tank for large demands, and the POU for instant hot water. Main tank serves taps close to the tank and provides large capacity to those served by POU.

[Steve Barker]

>>

Exactly. My washer is the farthest from the water heater, so there sits an electric 10 gal unit ontop the washer. Fed by the hot line from the main tank. Also there is a utility sink between the washer and dryer fed by that ten gal unit. No waiting.

[trader4]

Clearly it does not give you all the benefits of tankless.

[croy]

Hve you been able to determine if there is an energy savings after the point of use heaters were installed? Curios.

Certainly it would cut down on wasted water.

[Attila.Iskander]

>>

Point of use tanks are typically electric Where I am, electric would increase cost by a factor of 3+ compared to natgas.

[krw]

...and aggravation. Our new house has the water heater in the garage, at the far corner of the house from the master bath, about 100' of pipe. It takes seemingly forever in the morning for the shower to get hot.

In this house, the water heater is in the attic. The pipes to the kitchen go down two floors, under the slab, and over to the kitchen. The water to the dishwasher never gets hot.

At least the new house has an unfinished basement so a small point-of-use water heater would be trivial to install. Definitely a possibility.

[krw]

Like? A small electric heater wouldn't require a flue, a *big* advantage.

[Steve Barker]

i was not interested in energy savings. I was interested in having appropriate hot water in the washer and dishwasher. My gas bill never reaches the minimum with a conventional 40 gallon tank and the stove running on gas. The 1500 watts on the point of use tank is a moot point because it is fed with water that is 5 or 10 degrees hotter than it's set point. It rarely pulls any current.

[trader4]

ge. =A0- Hide quoted text -

Unlimited hot water. No standby losses 24/7 from multiple tanks.

[croy]

But it's a reservoir-type of water-heater, correct? There must be some energy use to keep the reservoir hot. I'm just wondering if it's an overall savings, or close enough to make me want to install here. If it turns out to be an energy loss by a substantial amount, I might give it a pass.

[krw]

Hide quoted text -

Backed by a 50gal tank it's pretty much "unlimited". I've never drained a water tank (don't have four daughters, either ;-).

That's a small issue, likely swamped by differences in fuel and purchase costs.