Posted by goldenhound on September 25, 2008, 3:41 pm
Can someone please tell me if this idea is feasible:
I'd like to pre-heat the water in my water heater (gas) and was
thinking that I could coil some copper tubing (or pipe same ID pipe as
the water supply) inside the vent pipe (about 4' in height) and take
advantage of the heat from the exhaust to pre-heat the water.
The normal-sized 4' vent pipe would be replaced with a bell-reducer on
both top and bottom and use a larger diameter vent pipe in-between to
hold the copper coil inside the vent pipe and not obstruct the flow of
the exhaust.
The design would be to re-route the water supply to the top of the
coil, and have it flow down toward the tank, come out of the vent pipe
and then into the normal cold water inlet to the water heater.
What's wrong with this idea?
Posted by daestrom on September 25, 2008, 4:35 pm
goldenhound wrote:
> Can someone please tell me if this idea is feasible:
> I'd like to pre-heat the water in my water heater (gas) and was
> thinking that I could coil some copper tubing (or pipe same ID pipe as
> the water supply) inside the vent pipe (about 4' in height) and take
> advantage of the heat from the exhaust to pre-heat the water.
> The normal-sized 4' vent pipe would be replaced with a bell-reducer on
> both top and bottom and use a larger diameter vent pipe in-between to
> hold the copper coil inside the vent pipe and not obstruct the flow of
> the exhaust.
> The design would be to re-route the water supply to the top of the
> coil, and have it flow down toward the tank, come out of the vent pipe
> and then into the normal cold water inlet to the water heater.
> What's wrong with this idea?
The basic idea is valid, but there are a couple of things to keep in mind.
1) The flue gasses have a lot of water vapor in them. When they hit
something cold the vapor will condense. If you have a quiet water heater,
you can probably hear intermittent 'hissing' when the burner is on from
water dripping off the inside of the tank's fire tube. That's water
condensing out of the flue gasses and dripping back down on the burner.
This condensate can be quite corrosive over time, that's why the tank's fire
tube is where most leaks start. So your coil will be subject to the same
sorts of problems. It might not last too long.
2) Don't cool the flue gasses down *too* much or you won't have any natural
draft. This could lead to some of the flue gasses coming out the back-draft
preventer break above the heater. And that's bad as the CO and CO2 could be
deadly. If you start getting unexplained headaches and 'flu-like' symptoms,
that's the early stages of CO poisoning. Get a CO monitor, it's a good
thing to have anyway.
daestrom
Posted by goldenhound on September 25, 2008, 6:59 pm
wrote:
> This condensate can be quite corrosive over time, that's why the tank's fire
> tube is where most leaks start. So your coil will be subject to the same
> sorts of problems. It might not last too long.
> 2) Don't cool the flue gasses down *too* much or you won't have any natural
> draft. Get a CO monitor, it's a good
> thing to have anyway.
Excellent suggestions Daestrom. Thanks for your insight.
Rob
Posted by Martin Riddle on September 25, 2008, 7:36 pm
wrote:
> This condensate can be quite corrosive over time, that's why the
> tank's fire
> tube is where most leaks start. So your coil will be subject to the
> same
> sorts of problems. It might not last too long.
> 2) Don't cool the flue gasses down *too* much or you won't have any
> natural
> draft. Get a CO monitor, it's a good
> thing to have anyway.
Excellent suggestions Daestrom. Thanks for your insight.
Rob
The newer burner technology that is being developed is based on this
same principal, but the main problem is the condensation, its quite
acidic.
Cheers
Posted by z on September 25, 2008, 6:59 pm
b2ca-78124e4c20b8@g17g2000prg.googlegroups.com:
> Can someone please tell me if this idea is feasible:
>
> I'd like to pre-heat the water in my water heater (gas) and was
> thinking that I could coil some copper tubing (or pipe same ID pipe as
> the water supply) inside the vent pipe (about 4' in height) and take
> advantage of the heat from the exhaust to pre-heat the water.
>
> The normal-sized 4' vent pipe would be replaced with a bell-reducer on
> both top and bottom and use a larger diameter vent pipe in-between to
> hold the copper coil inside the vent pipe and not obstruct the flow of
> the exhaust.
>
> The design would be to re-route the water supply to the top of the
> coil, and have it flow down toward the tank, come out of the vent pipe
> and then into the normal cold water inlet to the water heater.
>
> What's wrong with this idea?
Thats a cool idea. I wonder if I should do the same thing with my on-
demand heater. Just a coil above the burner that gives the water a bit
of heat.. might get slightly better pressure in the winter when its got
to work so hard to bring the ater up to temp.
XML site map
> I'd like to pre-heat the water in my water heater (gas) and was
> thinking that I could coil some copper tubing (or pipe same ID pipe as
> the water supply) inside the vent pipe (about 4' in height) and take
> advantage of the heat from the exhaust to pre-heat the water.
> The normal-sized 4' vent pipe would be replaced with a bell-reducer on
> both top and bottom and use a larger diameter vent pipe in-between to
> hold the copper coil inside the vent pipe and not obstruct the flow of
> the exhaust.
> The design would be to re-route the water supply to the top of the
> coil, and have it flow down toward the tank, come out of the vent pipe
> and then into the normal cold water inlet to the water heater.
> What's wrong with this idea?