Hybrid Car – More Fun with Less Gas

When is a Therm of Natural Gas not 100K BTU??? - Page 6

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Posted by Rob Dekker on October 22, 2005, 1:51 am


house.  In my case at least, the outside vent is

air drawn *into* the house when the unit is off.  But

top of the house.

off, there is still a small, constant draft of air

water back down, increasing the 'standby' losses.  If

from cooling the water off too much (i.e. the main

all summer long.

ignition, *that* would be something.  But it probably would

How about a air shut-off valve on the tank outlet which avoids draft when
the burner is off (or the air is cool) ?
That should not cost too much...

Posted by Solar Flare on October 22, 2005, 3:57 am
Could be dangerous without massive saftety mechansisms. what happens if it
doesn't open when it should?

Posted by daestrom on October 22, 2005, 1:15 pm

Well, the 'power-vent' model that I have has two safety mechanisms to
prevent the main burner from firing until the mechanical blower starts.
First, a small dP switch senses the negative pressure created in the blower
housing, and the 'bonnet' over the top of the tank's draft tube, at the
blower inlet has a high-temp shutdown switch.  If either one of these
determines that the blower didn't start (or it stopped prematurely), the
main gas valve shuts off.

The only downside is it cannot run when there is no electricity to power the
blower.  So an extra damper and position switch shouldn't add a lot more to
the system at this point.

I've thought about one of those outdoor vents for dryers that have a sort of
'ball valve' on the end to stop drafts from returning in the dryer vent line
when shut off.  Seems like the same range of temperature.


Posted by Solar Flare on October 22, 2005, 2:33 pm
 I had a problem with my power vent unit at the beginning of Labour Day weekend,
just before the kids went back to school. You know the weekend they should call
wash and laundry weekend instead?

Well, being a rental I couldn't get anybody else to touch it and the utility
renting wouldn't come unless I said I smelled gas, so my sleuthing skills
started to shine...LOL  "I can handle this...I am a polished instrument and
control  person"

WOW!   what a beast of interlocks these things are!   I can see what all the
things do and how every engineer in N.America has had their dibbs with it to
prevent every contingency possible.  I am surprised the MTBF (mean time to
breakdown failure)  isn't at about 2 working hours...LOL

Long story short. I found by disconnecting one sensor, with a normal closed
contact (it was NFG) , I could cycle the power and cause the tank to heat up
until it shut off normally. Then when I wanted another tank of hot water I just
cycled the power and it reset again.  When I finally got the service guy out to
repair it he freaked out. After quizzing a bit, I discovered he had no clue how
they worked or what the item did anyway but replaced it on my advice and his
little testing chart...LOL

The flap doesn't sound like too bad an idea. It probably would be no different
than a long vent pipe for air constriction anyway. Perhaps it would even make
the gases linger a little longer and increase the efficiency.

Keep your gas detector handy for the first ten years though...LOL

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