Ventilation of New Darkroom Question

I'm just completing the drywall on a new darkroom about 16'X10' with a 8'
ceiling ~1300 cubic feet. How much ventilation do I need? How do I calc.
CFMs/air exchange. How big a pipe do I need. I'm doing B&W, Color and maybe
Cibachrome work. The room is in a basement and I was thinking of tying into
an existing bathroom fan pipe (4" I'm guessing). Would I need to put a
backflow type of value to protect the bathroom? As I mentioned the bathroom
is adjacent to the darkroom. I've debated putting a vent in the wall between
the two rooms and keeping both doors closed and turning on the bathroom fan
while working too drawing the stale air into the bathroom and then out. Is
this advisable? (It is after all a basement bathroom) Thx. for any help with
this.

"SofaKing" wrote in message
news:qoLWb.469845$JQ1.90903@pd7tw1no...


Common sense tells me if you just attach to the existing vent pipe, the post
fan air flow will take the path of least resistance. That means if the fan
is at the top of the stack, it would be OK to attach the darkroom to the
same pipe. If the fan is built into the vent in the bathroom, you may end
up blowing all your fumes in there, unless you put a backflow flapper in
there.

If I recall correctly, the recommendation is 10 complete air changes per
hour. So you would need to move 13,000 CF per hours or 216 CFM. Most of
the manufacturers of darkroom ventilation products are using 6" ducting.

Hope this has been helpful.

Jim



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"SofaKing" wrote in
news:qoLWb.469845$JQ1.90903@pd7tw1no:

[...]
guessing). Would I need to put a backflow type of value to protect the
bathroom? As I mentioned the bathroom is adjacent to the darkroom.
I've debated putting a vent in the wall between the two rooms and
keeping both doors closed and turning on the bathroom fan while
working too drawing the stale air into the bathroom and then out. Is
this advisable? (It is after all a basement bathroom) Thx. for any
help with this.



When we put new fan in our bathroom (the kind where the fan is at the
ceilng), it had a backflow flapper thing where the duct attaches to the
fan. The one that was removed had one too. So you might already have one.

I would not put a vent into the bathroom except as a last resort, and if
I did it at all, I would make sure I could seal it off when it wasn't in
use.

Bob

Sofa* -- ASME (American Association of Mechanical Engineers) recommendation is
10 to 20 air changes per hour and I like 15 to 20 air changes per hour - in
part for removal of heat and moisture/humidity. And with 1300 cu.ft. something
around 350 CFM would do a good job for you.

Now, I recommend that you pressurize your darkroom - i.e. blow air into the
darkroom instead of sucking air out of it. The reason - it keeps the dust and
dirt out of the darkroom.

The typical bathroom fan is a blade type fan. Consider using a squirrel cage
blower - a much more positive movement of air.

In my case - I mounted a blower high on an outside wall of the darkroom - in an
unfinished part of the basement. The air flows down the wall between the wall
studs and exits near floor level. The exhaust vent is positioned high above
the sink.

Another comment regarding the flapper check valves - is good. --- Jerry/Idaho

On Thu, 12 Feb 2004 13:41:42 GMT, "SofaKing"
wrote:

I'm just completing the drywall on a new darkroom

A few ideas concerning fans:

Fans are often rated for "free air" airflow, which is much greater
than the actual installed airflow due to resistance in filters, ducts,
and vents. Use a fan with a "free air" CFM rating at least 50%
greater than your calculated required airflow.

Large slow fans are generally quieter than small fast fans. Many fans
are rated in "sones". The lower the sones value, the quieter the fan.

To minimize dust, pressurize the room and filter the supply air. I
built a frame to hold a "high performance" furnace filter over the fan
intake. This provides a filter area much larger than the fan input to
minimize resistance to airflow.

A timer switch for the fan will make it convenient to run the fan for
several hours after a darkroom session to dry out the room.

Locate the supply vent high on a wall to avoid blowing dust up from
the floor, and as far from the sink as possible to avoid blowing
chemical vapors around the room. Locate the exhaust vent near the
sink below nose level to draw chemical vapors away from your face.

In new construction, the cavity between wall studs can make a good
light trap. Locate one vent high and the other low, and paint the
interior of the stud cavity flat black. Be sure the supply air cavity
is clean (and filter the supply vent just to be sure.)


Chris Ellinger
Ann Arbor, MI

some zone plate photos: http://www.ellingerphoto.com/

Yes it's giving me a better picture. Thanks.


"Jim Phelps" wrote in message
...

"SofaKing" wrote in message
news:qoLWb.469845$JQ1.90903@pd7tw1no...


Common sense tells me if you just attach to the existing vent pipe, the
post
fan air flow will take the path of least resistance. That means if the
fan
is at the top of the stack, it would be OK to attach the darkroom to the
same pipe. If the fan is built into the vent in the bathroom, you may end
up blowing all your fumes in there, unless you put a backflow flapper in
there.

If I recall correctly, the recommendation is 10 complete air changes per
hour. So you would need to move 13,000 CF per hours or 216 CFM. Most of
the manufacturers of darkroom ventilation products are using 6" ducting.

Hope this has been helpful.

Jim




__________________________________________________ __________________________
___
Posted Via Uncensored-News.Com - Accounts Starting At $6.95 -
http://www.uncensored-news.com
The Worlds Uncensored News Source

Is that recommendation for darkrooms or houses in general? Most off the
shelf bathroom fans seem to be just over 100 CFMs. I'm thinking I'll have to
move up to something heavier to achieve 10-15 air changes.
The blower you describe it blows the air into your darkroom and it enters
the room at ground level?

"Jtown2354" wrote in message
...
Sofa* -- ASME (American Association of Mechanical Engineers)
recommendation is
10 to 20 air changes per hour and I like 15 to 20 air changes per hour -
in
part for removal of heat and moisture/humidity. And with 1300 cu.ft.
something
around 350 CFM would do a good job for you.

Now, I recommend that you pressurize your darkroom - i.e. blow air into
the
darkroom instead of sucking air out of it. The reason - it keeps the dust
and
dirt out of the darkroom.

The typical bathroom fan is a blade type fan. Consider using a squirrel
cage
blower - a much more positive movement of air.

In my case - I mounted a blower high on an outside wall of the darkroom -
in an
unfinished part of the basement. The air flows down the wall between the
wall
studs and exits near floor level. The exhaust vent is positioned high
above
the sink.

Another comment regarding the flapper check valves - is good. ---
Jerry/Idaho

Thank you that's a good idea about not blowing the air around the room. I'm
thinking I'll use three HVAC vents from Home Deport as the intake manifold
above the sink and joing them to a 4" or 6" pipe which exhausts outside. At
This point I could easily mount a fan to supply pressuse to the room under
the sink or opposite the sink.

"Chris Ellinger" wrote in message
...
On Thu, 12 Feb 2004 13:41:42 GMT, "SofaKing"
wrote:

I'm just completing the drywall on a new darkroom

A few ideas concerning fans:

Fans are often rated for "free air" airflow, which is much greater
than the actual installed airflow due to resistance in filters, ducts,
and vents. Use a fan with a "free air" CFM rating at least 50%
greater than your calculated required airflow.

Large slow fans are generally quieter than small fast fans. Many fans
are rated in "sones". The lower the sones value, the quieter the fan.

To minimize dust, pressurize the room and filter the supply air. I
built a frame to hold a "high performance" furnace filter over the fan
intake. This provides a filter area much larger than the fan input to
minimize resistance to airflow.

A timer switch for the fan will make it convenient to run the fan for
several hours after a darkroom session to dry out the room.

Locate the supply vent high on a wall to avoid blowing dust up from
the floor, and as far from the sink as possible to avoid blowing
chemical vapors around the room. Locate the exhaust vent near the
sink below nose level to draw chemical vapors away from your face.

In new construction, the cavity between wall studs can make a good
light trap. Locate one vent high and the other low, and paint the
interior of the stud cavity flat black. Be sure the supply air cavity
is clean (and filter the supply vent just to be sure.)


Chris Ellinger
Ann Arbor, MI

some zone plate photos: http://www.ellingerphoto.com/

I'll agree with all the suggestions here. Placing a "range hood" over a sink
can still result in the user being in the path of fumes moving from the sink
to the hood. I have seen designs which incorporate a length of perforated
pipe along the back of the sink attached to the vent flue which draws fumes
back away from the sink user. Positive pressure (pumping air into rather
than out of) should result in a cleaner darkroom. Use a furnace filter over
the air intake to the fan to prevent the ingestion of dust, and install some
kind of backflow prevention flapper on the bathroom fan stack to prevent
fumes being exhausted into the bathroom. I have used the partition
lighttrap idea too, and it works fine for me. The bigger the ductwork, the
better for airflow.

Of course, if some really ugly incident takes place in the bathroom, the
darkroom user could be in big trouble from bathroom fume backflow too....


"Chris Ellinger" wrote in message
...
On Thu, 12 Feb 2004 13:41:42 GMT, "SofaKing"
wrote:

I'm just completing the drywall on a new darkroom

A few ideas concerning fans:

Fans are often rated for "free air" airflow, which is much greater
than the actual installed airflow due to resistance in filters, ducts,
and vents. Use a fan with a "free air" CFM rating at least 50%
greater than your calculated required airflow.

Large slow fans are generally quieter than small fast fans. Many fans
are rated in "sones". The lower the sones value, the quieter the fan.

To minimize dust, pressurize the room and filter the supply air. I
built a frame to hold a "high performance" furnace filter over the fan
intake. This provides a filter area much larger than the fan input to
minimize resistance to airflow.

A timer switch for the fan will make it convenient to run the fan for
several hours after a darkroom session to dry out the room.

Locate the supply vent high on a wall to avoid blowing dust up from
the floor, and as far from the sink as possible to avoid blowing
chemical vapors around the room. Locate the exhaust vent near the
sink below nose level to draw chemical vapors away from your face.

In new construction, the cavity between wall studs can make a good
light trap. Locate one vent high and the other low, and paint the
interior of the stud cavity flat black. Be sure the supply air cavity
is clean (and filter the supply vent just to be sure.)


Chris Ellinger
Ann Arbor, MI

some zone plate photos: http://www.ellingerphoto.com/

"SofaKing" wrote in
news:qoLWb.469845$JQ1.90903@pd7tw1no:

I'm just completing the drywall on a new darkroom about 16'X10' with a
8' ceiling ~1300 cubic feet. How much ventilation do I need? How do I
calc. CFMs/air exchange. How big a pipe do I need. I'm doing B&W,
Color and maybe Cibachrome work. The room is in a basement and I was
thinking of tying into an existing bathroom fan pipe (4" I'm
guessing). Would I need to put a backflow type of value to protect the
bathroom? As I mentioned the bathroom is adjacent to the darkroom.
I've debated putting a vent in the wall between the two rooms and
keeping both doors closed and turning on the bathroom fan while
working too drawing the stale air into the bathroom and then out. Is
this advisable? (It is after all a basement bathroom) Thx. for any
help with this.



I would not vent into the bathroom. Some processes (especially toning)
release some pretty oderiferous gases - the domestic heat you would get
for dumping that into the bathroom would be miserable!

Here's my suggestion. First, plan on a system that provides positive
pressure in the darkroom. That means that the fan pushes air into the
darkroom from which it vents outward by natural flow. The reason for this
is that if the static air pressure in the darkroom is slightly higher than
outside, the flow of air through parasitic vents (around receptacles,
doors, etc) would take dust out of the darkroom rather than in.

Second, plan to filter the air flow to minimize the inflow of dust through
the ventillation system. For obvious reasons.

What I did in my basement darkroom was to construct a box between a couple
of ceiling joists outside the darkroom. I mounted a fan in one end of
this box, and put a frame around the box so that I could slip an ordinary
furnace air filter in to filter the air flowing into the box. The fan
blows out of the box. Then, I used a flexible duct to connect the outlet
of the fan to a vent inside the darkroom. The exhaust from the darkroom is
via a large "cold air return" louvered vent mounted directly over the
sink.

I actually used a bathroom duct kit from Lowes that included both a length
of flexible duct and a louvered flange that was intended for mounting
outside the house when the duct is used to vent a bathroom. The reason I
did this outside the darkroom was to minimize the distracting noise of the
fan inside the darkroom. In my case, I used a computer-style muffin fan
that was quiet to begin with - and in this arrangement, I can't hear it at
all in the darkroom. I wired it to the master switch in the darkroom so
that the fan is on whenever anything is being done in the darkroom and so
it goes off when I leave the darkroom and turn off that master switch.

The fan I bought is rated 60cfm. I suspect that with the duct, the actual
flow is somewhat less. My darkroom is about 800 ft3 - which results in a
very comfortable working condition.