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from: john shea
to: toddharrison@cox.net,
date: Fri, Feb 6, 2009 at 6:46 AM
subject: pool heater

Hey Todd,

I love your site. Pretty cool and very informative. I am writing you to ask for some help on my
project. I have been attempting to heat my pool in a short time period as well. I decided to change
up your design a bit but it is not going as efficiently as planned. I am using a foundry furnace
design instead of your fire box. My foundry furnace is lined with fire bricks and actually gets hot
enough to melt aluminum, copper, and bronze. At least two to three times hotter than your cajun
redesign. Since I have a hotter furnace I figured I could use less copper coil. I have enclosed
some pics. Each coil is 20 feet long and Between the two coils which run parallel the heater clears
400 gal per minute. The coil is 1/2 inch by the way. Each line clears 200 gal per minute. Each line
can raise the temp 25 degrees. Using your math I get about 100000 BTU. Way short of my goal. Also
im not using your cajun burners but I have fabricated my own. I know im getting plenty of heat and
my tank is also freezing from rapid gas loss. My assumption was that if I could just increase the
heat I could decrease the copper pipe lenth and have a more compact design. Well like I said 100k
btu is not enough. I figure I will have to redesign the whole thing and go for your design of a
lower temp and lots more copper. Before I begin I wanted to get your thoughts. I dont know how long
your copper pipe lenth is so I wanted to ask you about that. You said on your site to use 3/4 pipe
but I thought that 1/2 pipe would be more efficient. I also see that you used a manifold but I
thought that perhaps this parallel system would do essentially the same thing. I figure that nine
1/2 pipes would move the same volume of water as one 1&1/2 pipe. I figure that nine parallel lines
running thru my heater will allow 100% flow thru my heater using the pool pump. Would me 1800 GPH.
If this temp raises 20 deg would be 300K btu and if this raises 30 deg would be 450k btu. Obvously
the longer each of these runs is thru the heater the more time the water has to heat and the hotter
it comes out the other side. How long should each run be? My old design only allows two 1/2 lines
running thru and coming out 20 to 30 degrees hotter but then it mixes with the other 2/3 volume of
cold water which by passes the heater and returns to the pool only a couple of deg hotter.

John