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

Does anyone have experience with tnakless water heaters?

Yes.

Are they really cheaper than a central water tank?

Yes. And no. (See below.)

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

No.

What is the cost (roughly)?

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

Any detractors?

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.


--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)