On Jul 27, 1:16*am, Rick-Meister wrote:
Some demand heaters have a modulating gas valve......some. Not all.
And certainly not the low end units.

I'll say it again. I'm not saying that demand heaters aren't
efficient....they are. But there are a few issues with them regarding
efficiency across the board and low flow.

Geez guys, settle down a bit and read the whole post before you flame.
All I told the guy was to evaluate his usage and be aware that there
are some circumstances where the demand heaters, well, I'm repeating
myself.

End of discussion--at least for me.


Before it ends, I'd like an explanation and reference for a couple of
your statements:

"The higher the water pressure, the larger the BTU's required to
handle the same usage. "

This makes absolutely no sense. If the tankless is heating 5 gallons
of water, what possible difference in efficiency could it make if the
water pressure is 30 PSI or 60PSI? I have never seen anyone claim
that pressure factors in at all to sizing a tankless.

I also don't buy the analogy of comparing a tankless to constantly
refilling a pan heating water on the stove. You state that you are
constantly reheating the pan, as if the pan itself somehow takes and
holds heat. In reality, the heat is going into the water. Some is
escaping as loss around the pan, to the surroundings, but that happens
regardless of whether the pan is being refilled every minute or left
alone for 10 mins. In fact, MORE heat will be transferred to the pan
in the case of it being refilled with cold water, as the cold water
will absorb more of the heat without it being lost to the
surroundings.

If you refill the pan 10 times in 10 minutes, you wind up with 10 pans
of barely warm water. If you leave one pan sit for 10 minutes, you
wind up with one pot of hot water. If you think some energy
inefficiency is at play here, explain exactly where this lost energy
is going?