Rear venting Bosch 125 tankless water heater (vent height requirement)

Posted by ian on July 11, 2006, 9:57 pm

Hi-- I d like to to install a Bosch 125HX on an outside wall, and vent
through that wall. But my initial vertical height plus 45=B0 leg back
through the wall (which counts as vertical) don't quite make the 6'
vent height Bosch recommends. Is it a performance or safety issue with
a shorter vent? I want hot water when the grid's down, so trying to
make it work without powered vents! Thanks. --ian

Posted by DJ on July 12, 2006, 5:42 pm

ian wrote:

> Hi-- I d like to to install a Bosch 125HX on an outside wall, and vent
> through that wall. But my initial vertical height plus 45=B0 leg back
> through the wall (which counts as vertical) don't quite make the 6'
> vent height Bosch recommends. Is it a performance or safety issue with
> a shorter vent? I want hot water when the grid's down, so trying to
> make it work without powered vents! Thanks. --ian

Ian,

Just so's I understand. Bosch wants the vent 6' above what, exactly?
The heater, or the ground... and yes, I'm asking you rather than taking
the two minutes it would take to either check my own files or download
the manual from Bosch ;-).

If it's a rule, though, I'm thinking it's from Bosch, not the Code.
I've installed a few propane direct vent appliances, and they go on and
on about a MAXIMUM length of exhaust for non-power assisted vents, but
not a minimum. Minimum distances from windows, doors, propane storage,
all kinds of stuff like that, but not length of exhaust on the propane
appliance.
Might be that in a short exhaust, the incoming air doesn't have as much
time to warm up from the exhaust portion of the pipe? This would
degrade performance a bit.

DJ

Posted by ian on July 15, 2006, 10:42 am

DJ wrote:

> Just so's I understand. Bosch wants the vent 6' above what, exactly?
> The heater, or the ground... and yes, I'm asking you rather than taking
> the two minutes it would take to either check my own files or download
> the manual from Bosch ;-).
> If it's a rule, though, I'm thinking it's from Bosch, not the Code.
> I've installed a few propane direct vent appliances, and they go on and
> on about a MAXIMUM length of exhaust for non-power assisted vents, but
> not a minimum. Minimum distances from windows, doors, propane storage,
> all kinds of stuff like that, but not length of exhaust on the propane
> appliance.
> Might be that in a short exhaust, the incoming air doesn't have as much
> time to warm up from the exhaust portion of the pipe? This would
> degrade performance a bit.

Hi. I checked the installation instructions again and it states
''Minimum vent size must be 5". Minimum vent height must be 6 feet,
provided there are no elbows.'' It doesn't say what happens to the
vent height requirement if there *are* elbows, tho. I was thinking
about how chimneys work, and they do need to stay warm to draw well,
maybe that's what they're on about?

Posted by El Barto on July 14, 2006, 6:52 pm

>I want hot water when the grid's down, so trying to
>make it work without powered vents!

Umm...what about the power for the control electronics? Power vent or
no, you still need electricty to make hot water!

Posted by JerryD\(upstateNY\) on July 15, 2006, 8:13 am

> Umm...what about the power for the control electronics? Power vent or
> no, you still need electricty to make hot water!

There are no electronics on a Busch water heater, so it needs no electric to
make hot water.
--
JerryD(upstateNY)

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