[Greenbuilding] tankless water heater efficiency...

[Bruce Donelson]

>Electric storage heaters look good here, producing 95% of their energy
input.
>How much can a tankless improve that? Are any tankless units more
efficient?

>Nick

Electric tankless have slight standby losses, but the improvement over
95% is slight regardless.  More to the point, with electric in
particular, much of that standby "loss" isn't loss in the half of North
America that locates hot water heating appliances inside.  The loss is
just space heat, so even considering fuel price and control issues, it's
still not all "loss", for an effectively higher efficiency.  I'd like to
measure the (positive) impact of this on the performance of a GFX,
possibly slightly modified for capturing more batch flow heat (or has
someone already measured this?).


Standby losses on tankless heaters measure the amount of heat that the water
looses. Gas water heaters do not account for heat lost through the exhaust
pipe. This can be immense in some installtions. I installed a Bosch
on-demand water heater on the third floor of a house I built, and the 7"
diameter exhaust duct sucked enough air to slam doors! You couldn't get the
house to warm up in the winter until the door to it's room was
weatherstripped. Often the pipes on the inside of a house will freeze
because of the cold air coming down this pipe. This can be avoided by
installing a sealed combustion heater. These are more expensive, but more
efficient. The efficiency calculations of conventional gas-fired heaters do
not account for the heat lost via the constant stream of air (warmed by the
water inside the tank) that flows up the vent pipe.

Bruce Donelson
A Better Builder