GardenBanter.co.uk - View Single Post

26-08-2003, 10:02 PM

(RROLD1) writes:

Hello all,

I have purchased a pump with a rating that does not make any sense at all
(trusted the knowlegable sales staff).

Ha!

I am trying to figure out my cost per
month but the only specification provided is output watts. Now that I have
compared it to the next pump size down, I am really confused. I don't want to
install it if a smaller one will do the job.

Here are the specs:

My pump:
Rated 3800 GPH
Output Watts: 736

Next pump down:
Rated 3300 GPH
Output Watts: 330

No "at XXX feet of head" in the GPH spec?

After reading the specs I called the dealer and asked the average monthly cost
to run each pump. They replied that the smaller pump will cost about $28.00 and
the other (the one I have) about $64.00. There is only a 500 GPH difference! Do
they know what they are talking about?

No. The wattage is a maximum value. Throttling the output, for example, will
reduce the power draw.

After searching the newsgroups, I have found a lot of similar questions but no
difinitive answers (at least none that I understand).
Why don't the pump companies offer a table of actual killowats used per feet of
head?. Its the answer everyone seems to be after.

Did you look for this on the web? What brand of pump?

My GUESS is that the 3800 GPH is a high pressure pump and at the same GPH and head
the power consumption will be similar for both pumps, probably a little worse
for the bigger pump as its not optimally designed for low head.

You can measure the power consumption with a power meter or by looking at
your electric meter with the pump on and off and repeat until you get
stable answers. This is much easier if you can shut off all other breakers
except the one the pump is on. I have a friend who owns a disembodied electric
meter with male and female AC plugs, handy for this sort of experiment.

HTH