[PLUG-TALK] Another use for 12 volt fans?

[John Jason Jordan]

On Thu, 21 Sep 2017 17:42:52 -0700
Keith Lofstrom <keithl at kl-ic.com> dijo:

>On Thu, Sep 21, 2017 at 05:06:59PM -0700, Tomas Kuchta wrote:
>> Relying on this kind of active solution for safety inside a wall
>> build to outlast you seems like - what could possibly go wrong!
>> 
>> I suggest looking for passive systems such as radiation, separation,
>> chimney effect, heat resistant materials, etc. Or getting less heat
>> of your fireplace.

...

>But I concur with Tomas's major point.  Ultimately, while
>I like hacker endeavors, there are reasons why we purchase
>spendy HVAC solutions;  they can fail and kill people. 

First, thanks for the endorsement of Noctua. Mr. Google had already
introduced me to them, and your experience clinches it. Also, thanks
for pointing out that size matters. I had already intuitively grasped
that fewer larger fans would be better than more smaller fans, although
seeing the formula was instructive.

Regarding dangers and potential failures of my plan, I think that I did
not explain clearly enough. ~Ten years ago I bought the fireplace from a
shop on Broadway and had them install it, although I did the gas
connection. The fireplace has an opening under the firebox that is
about four and a half inches high, with a pull-down grille because this
is where the gas and thermostat connections are, as well as the pilot
light. In this area there is also a standard 120 volt duplex outlet for
the optional 'performance fan.' I did not buy the fan because this
fireplace was on display in the store with the fan installed, and it
was too noisy for my taste. The fan draws in room air, which is
basically air at the floor, forces it around the firebox and pushes it
out of a grille just above the firebox. This is one of the applications
for my plan. Note that the fans will draw in room air from the floor,
so there should be no overheating problems. I plan to put the power
supply there also. And since this is where most of the heat savings
will occur, I figure I will need a goodly cubic feet per minute. I am
thinking of three 4" Noctua fans for this location. Also note that the
fans and power supply are readily accessible at any time.

My second application will be the enclosure above the fireplace that
will contain the vent stack plus the mesh that I plan to attach for
better heat transfer. There will be far less heat transfered/saved here.
I plan on having two grilles, one at the bottom of the vent stack (just
above the fireplace) and another at the top, just below the ceiling. I
could make the air flow in at the bottom and out at the top, or
vice-versa. I figure it makes more sense for the air to come in at the
top and exit at the bottom, just because you always want your heat
source as low in the room as is practical. I was planning on mounting
the fans at the bottom grille, but I could easily mount them at the top
grille instead. Note also that the fans will be mounted to the back of
the grille, easily accessible for maintenance. And here I have no real
space limitations, so I could use 8" fans to produce greater airflow at
lower rpm.

Both sets of fans will run off the power supply in the lower
compartment. All I need to do is figure out how many watts the power
supply needs to be, considering that I would prefer a power supply that
can produce twice as many watts as my fans will need - no need to
skimp here. Hopefully I can find a fan-less power supply that has a
decent reputation. It can easily be replaced, but buying cheap is not
always the most economical alternative.