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Posted by ransley on March 20, 2008, 1:22 am
> On Wed, 19 Mar 2008 04:32:02 -0700 (PDT), ransley wrote:
> > 98% water heaters are common even 96% boilers
>
> I think the reason for this is somewhat misleading.
>
> If I understand this correctly, almost all the heat energy put into an
> electric heater gets put into the water. Basically, the water cools the
> heater coils down by taking the heat off the heater coil.
>
> In the case of a gas water heater, the water cools down the flame by takin=
g
> heat off the flame (figuratively speaking) but a LOT of heat goes up the
> flue.
>
> They baffle the flue to slow down the rising air but they have to let the
> hot air out. If they cooled the hot air to room temperature, it wouldn't
> rise and get out of the house and that would be a bad thing from the
> standpoint of carbon monoxide poisoning.
>
> So, I think the fact that all none of the heat energy that went into the
> electric coils goes up any flue - it's all absorbed by the water - is what=
> makes the electric water heater 98% efficiency.
>
> But, as someone stated, I suspect the power generation is about 70%
> efficiency, so, the true efficiency of electric water heating must be
> vastly lower than 98% taking distribution into account.
>
> But, how can we account for that true efficiency?
>
> Donna
Electric are all 100% efficent, all energy consumed is used to heat
water, and energy factor should be near 100 as well with great
insulation. Almost all gas water heaters burners are about 80-83%
efficent, but an additional 17-20% goes up the chimney 24 hrs a day,
Energy Factor ratings account for loss up the center uninsulated flue
part of the tank and reflect overall efficency, which for most gas
tank is 50-60 with one I saw of 70. Condensing gas water heaters,
Boilers, furnaces, are different, have a second exchanger that lowers
flue temp to near room temp and are forced out the flue by a fan. A
condensing 93% water heater wont loose 20% in flue loss since the fan
stopped some of the heat loss, but even the best condensing tank water
heater of 93% may only be 83% Energy Factor [I guess]. Condensing tank
water heaters are really commercial units costing thousands. AO Smith
has them, I own one a 175000 btu unit, a Cyclone. For most, electrics
are and always will be more expensive to run unless you have a cheaper
Hydro Dam nearby, since for most oil- gas products generate
electricity. Someone stated 70% for electric, that is not true to you
for what you consume and pay, he was talking about transmission line
loss, for you electric tank is 100% efficient, but here electricity is
still 30% more than NG. If nobody in your neighboorhood has an
electric furnace then you can bet Ng is still cheaper per Btu. Now in
the last 6 months all petroleum products are going up fast, but
electric will follow in the long run.
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