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<DIV>If you do not use direct air feed such as the 6” duct to boiler in this
example, you will be counting on the equivalent clear area from random cracks in
the thermal envelope. On most common practice houses, this may seem like a
reasonable assumption. However, as the houses get tighter, this draw will
depressurize the house and have more difficulty drafting, creating opportunity
for backdrafts and CO, smoke entering the thermal envelope. The duct for
direct feed to combustion appliances in a closed loop is not a hole in your
thermal envelope if it remains tight and separate from the air in the
conditioned space. A combustion appliance is required to loose some heat
to vent toxic fumes. Eliminating the vulnerability to back drafting is a
huge benefit to closed loop combustion appliances. The newer more
efficient equipment I think have a forced draft that does not rely on the
chimney affect of heat rising to vent. I think this allows the combustion
gases to go through some heat exchanger and therefore improve the efficiency.
The 6” hole of the air feed vent is only a hole for conductive heat loss, not
the higher convective heat loss of a hole that is open from outside to the
conditioned air. I suppose one could insulate the outdoor air feed duct up
to the combustion appliance to reduce the conductive heat loss. </DIV>
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<DIV>Eli </DIV>
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<DIV style="font-color: black"><B>From:</B> <A title=norbert.senf@gmail.com
href="mailto:norbert.senf@gmail.com">Norbert Senf</A> </DIV>
<DIV><B>Sent:</B> Wednesday, January 14, 2015 4:04 PM</DIV>
<DIV><B>To:</B> <A title=greenbuilding@lists.bioenergylists.org
href="mailto:greenbuilding@lists.bioenergylists.org">Green Building</A> </DIV>
<DIV><B>Subject:</B> Re: [Greenbuilding] Fresh air to boiler
questions</DIV></DIV></DIV>
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<DIV dir=ltr>The air consumption of an 80,000 BTU/hr boiler is in the range of
25 cfm while it is operating. Heating that combustion air by 50 degrees F
requires about 3,000 BTU/hr, which happens no matter whether the outside air has
a direct or indirect path to the burner. Having a 6" dia permanent leak in
the basement is a really inefficient way to do it. There is no good engineering
reason to have that leak, unless your basement is hermetically airtight and 25
cfm would depressurize it enough to cause the boiler or water heater or (worst
case) an open fireplace to backdraft. This is generally considered to be -5 Pa.
Much more likely that a 250 cfm kitchen exhaust hood would do it, assuming that
your basement is not sealed from the rest of the house. Clother dryers and
bathroom fans also, are in the 100 cfm range.<BR></DIV>
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<DIV> </DIV>
<DIV class=gmail_quote>On Tue, Jan 13, 2015 at 7:43 PM, Benjamin Pratt <SPAN
dir=ltr><<A href="mailto:benjamin.g.pratt@gmail.com"
target=_blank>benjamin.g.pratt@gmail.com</A>></SPAN> wrote:<BR>
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<DIV class=gmail_extra>I have been sealing up and insulating the unfinished
portion of my basement, but am concerned it is a waste of time and money:
There is a 6" fresh air duct to provide proper combustion for the boiler.
Also, there is no damper on the water heater or boiler. Therefore, a lot of
cold air is continually dumped into the basement, and a lot of hot air escapes
up the chimney.</DIV>
<DIV class=gmail_extra> I suppose the solution to this would be to
install a new boiler, and to install a direct vent kit on the water heater.
The boiler is around 15 years old, and is 84 percent efficient. If I buy a
more efficient boiler, that is direct vented, any guess as to how much energy
I will save? I suppose its more then just the amount of natural gas I will
save with a more efficient boiler, since I would also be eliminating a huge
source of air infiltration. I would like to be able to calculate the ROI, so
my wife agrees to the purchase.</DIV>
<DIV class=gmail_extra>I'd appreciate any help you can provide.</DIV>
<DIV class=gmail_extra>Thanks,</DIV>
<DIV class=gmail_extra>Ben<BR clear=all>
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<DIV> </DIV>
<DIV> </DIV><BR>b e n j a m i n p r a t t
<DIV><BR>professor art+design</DIV>
<DIV>the university of wisconsin stout</DIV></DIV></DIV></DIV>
<DIV> </DIV>
<DIV class=gmail_quote>On Tue, Jan 13, 2015 at 3:46 PM, Sacie Lambertson <SPAN
dir=ltr><<A href="mailto:sacie.lambertson@gmail.com"
target=_blank>sacie.lambertson@gmail.com</A>></SPAN> wrote:<BR>
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<DIV style="FONT-SIZE: small; FONT-FAMILY: verdana,sans-serif">I'm looking
for an architect in Seattle who understands energy efficient good building
and does contemporary design work. Welcome suggestions.
Best to send these off the forum, to me directly.
Sacie<BR></DIV></DIV><BR>_______________________________________________<BR>Greenbuilding
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<DIV> </DIV></DIV></DIV><BR>_______________________________________________<BR>Greenbuilding
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clear=all><BR>-- <BR>
<DIV class=gmail_signature>Norbert Senf<BR>Masonry Stove Builders<BR>25 Brouse
Road, RR 5<BR>Shawville Québec J0X 2Y0<BR>819.647.5092<BR><A
href="http://www.heatkit.com" target=_blank>www.heatkit.com</A></DIV></DIV>
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