Re: OT / Tankless Heating

[Lee Hart <leeahart@earthlink.net>]

>> As a side note, many Europeans use a tankless, on-demand water heater.
>> I've heard that they are more efficient than storing a big tank full
>> of hot water.

> Actually, they are less efficient... While heating
> Kind of like needing a bigger motor to accelerate quickly.

"Efficiency" is not the word for what you are talking about; it's
recovery time.

American-style water heaters are just a big water tank and small heating
element (usually gas or electric). The amount of hot water they can
produce continuously (gallons per minute) is rather low; so they have a
big storage tank. It can then spend half an hour heating the water for a
5-minute shower.

European-style water heaters have no storage tank, but a bigger heating
element (also gas or electric). They can produce more gallons per minute
of hot water. But for cost/power/size reasons, they are usually sized to
be barely adequate for a warm shower at low flow rates. 

Overall energy efficiency of the American system is much worse. First,
because the water is typically hotter. Second, because Americans spend
longer in their baths and showers (perhaps because it is warmer). Third,
because there are standby losses to keep that tank of water hot all the
time. The result is that Americans typically use 3-10 times more energy
per capita for home water heating than Europeans (varies depending on
country).

You *can* get a demand heater with a big enough heating element to
supply a sufficient volume of hot water even at the highest flow rates
you might use. Restaurants, hotels, and similar businesses use this
type. But they have a pretty high power consumption!

> >Where they are even more extra efficient is when you have
> >gas heat instead of electric and electric start..<no pilot light>..

The subject of "efficiency" in water heaters is seriously screwed up by
the regulations (thanks to heavy lobbying by water heater
manufacturers).

First, resistive heating elements are by definition 100% efficient.
Every last KW is converted to BTUs. No gas burner can come close to
matching this efficiency. But gas is (usually) cheaper per BTU than
electricity, so gas heating costs less. Here's an example from my most
recent electric and gas bills. Note: My gas rates have nearly tripled
from last year (!) but gas is still barely cheaper than electric heat.

electric: $0.0635/kwh x kwh/3409.5btu x 100,000therms/btu = $1.86/therm
gas: $0.97/therm / 80%efficiency = $1.21/therm

The standing pilot light in a gas water heater does NOT reduce
efficiency. The heat from the pilot also heats the water; almost as
efficiently as the main burner, in fact. The real reasons for
regulations to eliminate the standing pilot are much more complex and
political. (Don't get me started; I worked for Robertshaw, the largest
manufacturer of water heater gas valves, when this stuff was going
through).
-- 
Lee A. Hart                Ring the bells that still can ring
814 8th Ave. N.            Forget your perfect offering
Sartell, MN 56377 USA      There is a crack in everything
leeahart_at_earthlink.net  That's how the light gets in - Leonard Cohen