Tankless water heaters

[Prof Wonmug]

Does anyone have experience with tnakless water heaters?

Are they really cheaper than a central water tank?

Do I need one installed next to every hot water tap?

What is the cost (roughly)?

Any detractors?

[The Daring Dufas]

I've never had a water heater tank me, they are all selfish and very rude. 8-)

TDD

[Oren]

The ones I've seen installed were in new construction. The owner loves them; three units in a 5000 sq ft house that are on separate zones. His were mounted outside the home (in stucco) located in the desert.

Have a look at this buying guide.

[ELGY]

My daughter has a very large two story home. She installed two tankless water heaters, one for each floor. She loves them. Very little wait for hot water to reach a particular location and water is only heated when needed.

[David Nebenzahl]

On 11/9/2010 3:01 PM Prof Wonmug spake thus:

Yes.

Yes. And no. (See below.)

No.

If you're talking about the cost of the heater itself, a lot more than a tank-type heater.

Yes. And no.

(This subject has been discussed extensively here in the past; you might do well to browse some old threads here.)

The problem with tankless (aka "demand" or "on demand") water heaters is that they were overhyped, back in the 19-ought-70s, to be the do-all and end-all in efficiency and conserving energy.

Turns out that they *can* conserve energy, in some situations, depending on several factors. However, they can also *increase* your energy consumption in some cases.

Best to go back to basics: how do they work? (It's surprising how many folks talk about them without really knowing this, so it seems useful to go over this here.)

A regular tank-type heater heats a large volume (10-40 gallons) of water with a relatively small burner that uses a relatively small amount of gas. It keeps that tank at the temperature set on the thermostat, so it uses this small amount of gas periodically as the water is used, and as the water cools in the tank.

A tankless heater has no tank, as you'd expect. Instead, it uses a heat exchanger--basically a radiator in reverse--over a burner which uses a

*lot* of gas. A *lot*. But it only heats the water as it's being used; the flame goes on when water is drawn (i.e., when someone opens a hot water faucet), hence the "demand" part. When no hot water is being used, no gas is used at all. (Newer tankless heaters use electronic ignition, so no pilot light.)

The thing is, the tankless heater can save you money on gas, but it depends on a couple factors:

o The distance from the heater to the farthest hot water outlet o The usage patterns of the household

The latter one is the most important. I'm not an expert in this field, but it seems obvioous to me, at least, that if a household uses a lot of hot water throughout the day--say, doing a lot of laundry plus hot showers--then a tankless heater could actually end up costing more. Why? Because in order to heat the same amount of water as in a water heater tank, the tankless heater is going to use a lot more gas.

It'd be nice if there was some clear explanation of this out there in Web-land, maybe even some kind of online calculator or something. But the moral of the story is, you need to do some investigation, look at your water usage patterns closely, and don't get sucked in by hype about tankless heaters (either pro or con).

That's my story and I'm sticking to it.

[Ala]

Each cup of tea represents an imaginary voyage. ~Catherine Douzel

[SBH]

From what I understand, adding a tankless system in a new construction will provide payback in savings. Adding to an existing home will pay back in 15 to 20 years (or more), depending on usage. It is not recommended to add to an existing home. Chances are you'll sell the home before you gain what you paid.

[Oren]

Actually, a retrofit is viable if the OP has proper sizing for water/gas/electrical (which need).

We just don't know if he is comparing pomegranates to persimmons.

[Robert Neville]

Even that is doubtful. You have to add the increased cost of the unit itself, the increased cost of installation (including larger electric or gas service), and required annual maintenance. The operating costs for energy can be higher as your rate is often dependent on the size of the service.

Storage tank heaters are far more efficient than people realize. There are specific circumstances where demand heaters make sense, but economics aren't usually the reason.

[Steve B]

Yes. I investigated them. The upside is that they will cut your costs. The downside is that the large ones require a high amperage feed, hence big lines and breakers, and the water that comes out is only so hot. The cost of running electricity to every supply can be done if you are in the construction phase without as much cost as a retrofit.

I have no idea about the propane ones, but imagine with the cost of propane and natural gas going up, that their operational costs may be high.

Let's hear more from people who actually have them. I just checked into the ups and downs of getting one, and my electrical feed was insufficient, the cost to upgrade was high, so that was that.

Steve

[Sjouke Burry]

I have had instant hot water with natural gas for

35 years(a rental unit),capacity enough to fill the bath in reasonable time. No problems, and regular yearly maintenance from the rental company. At work we had the a small electrical unit in the garage for washing your hands, very handy, luke-warm water within seconds.

[Sjouke Burry]

Oh, the rental of the gas unit is 136 Euro per year, maintenance or replacement included. And the price of energy for gas is much lower here then the cost of electricity, so it is also used for heating.

[Prof Wonmug]

Do you know what brand?

[ransley]

Answering all your questions is a big job but here are some quick points, I have a 119000 Ng Bosch got it for 500 and its good for 1 shower and I never need it on high even with 40f incoming water. Instalations fail when you dont do your homework on your gas supply and incomming winter water temps and use. They use alot of gas and need all of it in winter to give you rated output, in winter on the coldest days gas can have reduced flow from the supply and has to be figured in. For 2 showers you need to go up to a 190000 btu unit, kids will ruin any saving knowing HW is endless. Savings go down percentage wise the more people you have and it may not payback with a family of

4-5. A single person will save the most, I got a 4-5 year payback but did my own install. You need to do alot of research and testing before buying one, it may or may not be a good idea for your situation. Is getting the needed gas supply means new piping, and instal is difficult, the cost of a 190000 btu unit can be thousands.

[mike]

I just got a tour of my friend's new system. It's about the size of a bathroom medicine cabinet. Has three 240V 40Amp heaters. 120A is no big deal for him cause he just put in 400A service. For most people, that would be a problem. Also, there's the major expense of the electrical work if you have to pay to have it done.

Gas would have it's own set of issues.

Once you've picked an energy type, you pay the same to heat water no matter what technology you use. A BTU is a BTU. The only difference is the losses in the system. If you use a lot of hot water, I can't imagine it saving much of anything. If you use no water, the energy saved by not radiating from your hot water tank and the pipes between the source and the point of use might be a significant percentage...but still maybe not a big absolute number of $$.

Might be a different situation if your house was optimized at design time to with all the points of use a short distance from the tankless.

[The Daring Dufas]

Bosch manufactures an interesting NG tankless heater that has a small generator powered by the flow of water through the unit that supplies electricity to the control system and electronic ignighter. With no standing pilot light, it's one of the more economical NG instant water heaters I've seen.

TDD

[The Daring Dufas]

Me and my friend installed an electric two module instant water heater for his sister. It's installed in the utility closet with the washing machine and electrical panel so we didn't have to run a lot of wire. The only problem with it is adjusting the rate of flow. For that, we installed ball valves to adjust how fast water goes through the heater. A gallon bucket and a stopwatch is what we used to determine rate of flow so the heater will work. What most folks don't understand about tankless water heaters is the fact that you're not going to get the full flow of the rest of your water supply unless you install a very high capacity heater. The water has to spend enough time in the heat exchanger to absorb the heat. If I installed a tankless heater for myself, I would add a tempering tank to help bring up the temp of the incoming water.

TDD

[Caesar Romano]

On Tue, 09 Nov 2010 15:01:40 -0800, Prof Wonmug wrote Re Tankless water heaters:

No. Compared to a well insulated conventional water heater, the pay-back for the tankless is longer than it's service life.

There may be other reasons that make it worth while, but cost saving isn't one of them.

[hallerb]

For many tankless no electric means no hot water at all.... Cold shower for you:(

At low flow the heater may not trip on:( and theres a delay between trip on and hot water thus wasting some water....

the install cost can be very high.

forget electric tankless few homes have the 400 amp main needed because over 200 amps is needed just to heat weater

if you live where its cold in winter the colder incoming water may not be hot enough seasonally...

theres more now ransley can jump all over this.....

the thing is all you save are the standby losses.

so run a experiment when you wouldnt be home for the day.

set heater to vacation, and check water temp when you get back home that night, note it wouldnt have fallen much...

thats all you will save after spending a boatload of money. and take note if you live where its cold in winter the water heaters standby losses help heat your home.......

tankless savings are way overstated.

spend the money on additional insulation that really helps

[trader4]

What is your basis for the above? It would seem to me that both a tank heater as well as tankless are going to get about the same amount of heat out of a given amount of gas that goes in. The tankless just uses a lot of gas or electric over a short period of time, while the tank type uses less over a longer time. If anything, I would suspect that a tankless is more efficient compared to a std efficiency tank water heater. The main energy savings AFAIK, comes from the elimination of the standby losses from a tank type heater. Whether that savings is enough to pay for the cost difference, including install, is questionable.

And I fail to see what relevancy the usage patterns have, at least with a typical whole house unit. If I use X gallons of hot water, what difference does it make when I use it, unless the point here is that with electric units there could be a time of day difference in rates for some? With a typical whole house unit installed somewhere, you're going to have piping losses with either type. And if you put in mutiple tankless to cut down the delay time for hot water, I would think the increased cost would take so long to recover you may never come out ahead.