Real Estate Forum

HVAC Guy wrote:
> Bob Pietrangelo wrote:
> 
>
> Remember the following:
>
> 1) this is a two-stage (or double-unit) furnace.  I will dig-up the
> model number and post it later.  This unit was sized and installed in
> 1981 to heat only the upper floor of a small commercial office
> building.  The upper floor is about 3000 sq. ft.
>
> 2) The second unit rarely, or never, comes on during the day, and I
> believe it only comes on when the thermostat calls for heat in the
> morning when the setpoint changes from 63f to 71f.
>
> 3) I have turned down the burners on the first unit (the second unit
> has a manifold gas valve that is not adjustable).
>
> 4) there is no barrier inside the furnace (from side-to-side) in the
> burner galley area, so the 2 intake vent lines (4" diam) can
> essentially feed both sets of burners (when they're both in use) or
> feed air to only the first set of burners (when only one side of the
> furnace is running).
>
> What this means is that you need to consider a situation where 4
> burners running at reduced gas pressure are drawing primary and
> secondary combustion air from two 4" flex lines (combined area = 25 sq
> in.) equivalent to a square duct 5" x 5".
> 
>
> Like I said, I will post the furnace model number and see if there's
> any info on the internet about it, like BTU output.
> 
>
> (I'm adding "?" to your quotes because you don't seem to be putting
> them in yourself)
>
> The furnace has only 1 motor (I think it's 3/4 hp) and it drives both
> blower fans.
>
> And like I said, the second furnace rarely comes on when I'm there to
> watch.  I would bet that it only comes on during the initial heat
> ramp-up in the morning.
> 
>
> Yes.
> 
>
> No idea.  I don't have a meter to measure this pressure, and I don't
> particularly care to do it anyways.
> 
>
> In the furnace room right beside this double furnace is a single
> furnace (whisper heat, electronic ignition, motorized damper gating
> the primary air intake).  This is for the lower level of the
> building.  It's flue is being fed into the 12" stack mentioned above.
> That furnace is not in use this heating season.
> 
>
> I don't know.
> 
>
> Prior to my modification, the furnace room was very cold in the winter
> because it had essentally an open vent directly to the outside.  By
> closing that vent, and ducting air from it directly to the furnace
> cabinet, the room is no longer cold.
>
> And in it's original state, the draft air would have been cold anyways
> because as I said the room was cold.  Not only that, but bottom of the
> furnace cabinet was raised about 1" above the floor, allowing the fan
> to pull some amount of cold air directly from the furnace room.
> Internally, the bottom of the furnace was not closed or sealed.
> 
>
> I don't see Mr. Storm's posts because he posts from Road Runner.  The
> news server I use automatically cancels posts from Road Runner because
> a lot of spam and flood posting have come from Road Runner over the
> past few months.  By all accounts, Road Runner is an irresponsible
> operator when it comes to usenet.
>
> I also don't see posts from:
>
> .p.jm@see_my_sig_for_address.com
> nicksans...@ece.villanova.edu
>
> because their posts are also being deleted by the news server I use
> (I'm not sure of the reason why in those cases).
> 
>
> The "scientific" answer is that I am seeking to limit the amount of
> cold-air infiltration into the building, and I'm achieving that by
> ducting primary combustion and draft air directly to the furnace
> cabinet thereby creating a closed combustion system similar to (I
> assume) the design technique used by high efficiency furnaces today.
>
> And by reducing the heat output of the burners, I am essentially
> modulating the furnace so that I am capturing a higher percentage of
> heat and increasing the furnace run-time duty-cycle (again I believe
> the same techniques are used in modern high efficiency furnaces).
> 
>
> The climate that I experience is similar to Chicago, Detroit,
> Cleveland, Buffalo or Toronto.

You can not reason with this dumb XXX.  Give it up.

If you read your Whitman / Johnson, you would have seen that - if you duct
in combustion & dilution air, your requirements are 1 sq. in., per 1,000
btu/h input to the appliance.  If your crappy furnace is a 100,000 btu/h,
you need at least 100 square inches for both combustion and dilution.  Older
draft hood furnaces will require 29 cu. feet of air to 1 cu. foot of fuel
burned.  That's 1 cu foot of fuel, 10 cu. foot of air to burn, 5 cu. foot of
secondary air, and 15 cu feet of dilution.  Any change in that will
interfere with the combustion process.  Also, you need 3.5 in. w.c.manifold
pressure feeding the burners.  Anything less will interfere with complete
combustion.  The result of which will be aldhyde formation, CO, and soot.
If, for any reason, your soot plugs up the inside of the heat exchanger
(over time) you will smoother the burner flame and have an even more
hazardous condition than the one you're creating.  Be well advised that if
your utility saw what you did, they'd red tag the furnace.  And, if you
persisted in arguing with them, they'd shut off the fuel service because it
is a hazardous use of the fuel.

All of this does not include ventilation around the appliance.  Most
furnaces are approved with 0" clearance in the back, 1" clearance on the
sides and 6" clearance in the front provided that you have ventilation to
cool the appliance.  [Look at the nameplate tag on the furnace.]  Keep i
t
up, you will have a fire some day if you don't kill someone first.

And BTW:  the draft hood serves two purposes, one is to prevent backdrafting
to the burners.  By enclosing the drafthood, you've given an opportunity for
a backdraft.

One of the problems with ducting in the combustion air is the opportunity
for blockage.  Those furnaces with direct venting approval, have pressure
controls to monitor this.  You do not.

The only thing you did good, was to seal the return air on the bottom.
[Required to prevent conditioned air from mixing with the combustion air
.]

--
Zyp

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