9 - air

The tricky part of making a darkroom is not darkening it but ventilating it. After all, now its windows and doors are sealed! So we’ll look at ventilation first and darkness in the next chapter.

Even trickier is making it quiet. With noise pollution, we are usually at the mercy of our neighbors whereas with air pollution, we could buy a purifier if necessary. Ventilation most affects the silence of a darkroom. It also affects temperature. Let’s examine each condition and see how they work together in a mechanical system.


Below, I will give design constraints and describe various systems of ventilation. But I will first address its physiological importance.


I have observed a shocking number of people who seem oblivious to their own need for fresh air. Even though everyone knows we die within minutes without air, the importance of constant fresh air has somehow escaped many. I can only attribute this negligence to mass psychosis, my explanation for other appalling features of civilized life. At the risk of insulting your intelligence, I am bound to address this fact of life, though it is one of the most basic, most obvious ones of all.

Fresh air is always important. It is a normal condition of life and, along with warmth and safety, one of our most urgent necessities. Every second of our lives, quintillions of organic processes occur, and virtually all of them require oxygen. It is the most important nutrient we consume. We can live days without water and weeks without food. Not so, air.

Just like food, air becomes a part of one’s organism with every breath. This affects quality of life to a very great degree. Though it weighs little, the amount of air you breathe weighs twice as much as the food you eat. In a darkroom, you have little to do all day besides breathe. So if you haven’t usually paid attention to air quality, you will likely notice it in darkness.

Whether you do or not, poor air quality cancels most benefits of a retreat. Intermittently airing the room out does not work. I mean opening the door a couple times a day with eyes covered. Put this approach out of your mind. This is darkness, not the dark ages. Whatever it takes, always provide yourself with continuous fresh air and especially in darkness.

This means either:

  1. following the instructions below
  2. hiring an HVAC contractor to clean, repair, replace, or install ventilation in your home
  3. moving somewhere the ventilation system just works (like the tropics or a new house in northern Europe)
  4. using oxygen producing plants
  5. a combination of these

Somehow, it must be done. Forget darkness a moment. We have no more urgent concern in life than arranging to breathe fresh air continuously and comfortably. Not freezing to death and keeping safe from injury present only rare exceptions to this rule. Keeping it foremost in your thinking about darkroom design construction will help ensure a successful retreat.

  • provides plenty of fresh air
  • absolutely lightproof
  • silent: hum and harmonics from fan and exterior noises extinguished
  • comfortable temperature: no undesired cold drafts
  • economical: ie, no wasted heat to the outdoors. This is more involved and a lower priority than retreating itself, so don’t get stuck on it. It requires a heat recovery ventilator (HRV). Besides significantly lowering heating costs, an HRV improves air quality and comfort in nearly all climates. More about it below.

Somehow, fresh air has to get into the darkroom and stale air has to get out, without letting in noise or light.

In the terms of the HVAC industry (Heating, Ventilation, Air Conditioning), the fresh air vent is the supply and the stale air vent is the return.

Sometimes, supply and return vents exist in the same room. This is the fanciest version of balanced mechanical ventilation. If your place has it, thank your lucky stars. Just make sure it runs continuously. Unless your room is huge, intermittent is not good enough.

More commonly, balanced systems put supplies in bedrooms and living rooms, and returns in kitchens and bathrooms. This means air escapes a bedroom around the door. Unless the space outside the door is totally dark, this calls for a threshold lightproof vent (plans below).

Balanced systems are rare. More common are negative pressure systems: bedroom and living room windows act as passive supplies and bathroom and kitchen exhaust fans as active returns. In this case, a lightproof multi-purpose helix vent, built into a window blind, is the supply. Or a silencer if noise surrounds your dwelling. A threshold vent is the return, letting stale air escape the bedroom to the exhaust fan.

Rooms with totally passive ventilation rely on open windows, exterior vents, and infiltration through cracks (that will get sealed against light). Such rooms will need helix vents in blinds at different heights to take advantage of convection. But they probably call for a fan and a silencer, maybe ducting.

By closely observing buildings I have discovered some simple ways to ventilate them. Sometimes rooms have lightproof and sound-dampened holes built into them in unexpected places:

  • unused holes for pipes, wires, chimneys, and ventilation.
  • behind a cupboard or inside a closet
  • a removable panel or piece of trim that could be temporarily replaced with a panel with a hole in it.

For example, I once found a cosmetically damaged door in the garbage at a building supply store exactly the same size as my darkroom’s door. So I stored the original door and cut holes in the damaged door for ventilation.

Another darkroom had no ventilation or suitable holes anywhere. Except it had no door. So we built a frame inside the doorway with a narrow door on one side and a narrower panel on the other. We cut holes in the panel for ventilation ducts. We fixed the frame in the existing doorway with metal straps screwed into old hinge holes. So we left no trace when dismantling the darkroom.

Similarly, we hung 7m of ducting that ran through three rooms; attached a silencer to it; made three window panels; and imperfectly covered five more windows with only one new screw hole in the entire rented house. And that hole was invisible behind a loose piece of trim. “Leave no trace” is a fun game that often improves design.

Sewage pipes drain downward but are ventilated upward. Once, friends and I replaced a flush toilet with a composting toilet. The exposed drain pipe, being oversize and in a single-story house, wasn’t subject to backflow. So it proved a perfect exhaust duct for a case fan at floor level. Imagination conquers all obstacles (and renews itself in darkness).


Here are further design constraints, photos, plans, and instructions for making and installing lightproof vents.


(helix vent specifications in parentheses / helix sr version)
{threshold vent specifications in curly braces}:

  • durable (protected by cardboard shell or silencer){subject to damage by kicking but easily rebuilt and can be made of sheet metal or shielded with cardboard or thin wooden boards}
  • thin enough to fit between blind and window (80mm) or door and threshold {adjustable}
  • cross-sectional area >75cm2 (90cm2){60–120cm2}
  • fully traps light, sending light around at least 5 corners (7 corners / 5 corners){6 corners}
  • short airway (240mm / in-silencer version, 160){140mm}
  • minimal size (87 x 220 x 216 / in-silencer version 87 x 148 x 260){fits under door, sticks out 20mm each side and up 60mm}
  • easy to make (so-so){yes}
  • elegant (yes: simple compact form, uses common materials, zig-zag-shaped passage accommodates natural helical movement of air){yes}
  • cheap ($4 in materials, 2-hour assembly time){$2 in materials, 1-hour assembly time}
helix vent

photo: helix vent, complete

This photo is of the old helix vent. The new one is shorter, narrower, thicker. At the edge opening, the cardboard has a lip and the core has flaps.

plan: helix vent, assembly
plan: helix vent, channels
plan: helix vent, inner wall
plan: helix vent, outer wall
plan: helix vent, shell
plan: helix vent, slot


I call it a helix vent because of how air actually moves through it: like a corkscrew. It might look like air would zigzag through like light. But air is a fluid like water and takes the path of least resistance. Which is to maintain the same curved trajectory by helixing through. Because the helix is the natural form of fluids in motion under any circumstance, this minimizes friction within the airstream as well.

The helix vent can go anywhere. Flaps of either its edge or face opening poke through a slot and get taped or glued down to the other side.

  • blind: attach it to the back of a blind and crack the window behind it.
  • door: cut slot(s) in it and use helix vent instead of a threshold vent.
  • wall (leading outside or to another room): attach vent to a flat cardboard box and attach box to the wall over the vent. Vent can be either supply or return
  • silencer
    • outside: with shell, attached at face opening
    • inside: without shell, attached at face or edge. I also made a second “s” version (s for short, straight, silencer). It is simpler, more efficient, higher capacity that attaches at the edge. It has fewer light-stopping corners and no shell, so it is only for installing inside the silencer or other enclosure with two or more corners. S version drawings in next section.

If your darkroom’s ventilation is passive, put vents both low and high in room to enable convection. This works better the greater the inside and outside temperature difference; the greater the vertical distance between vents; and the more vents.

Do you need a more compact vent? I used the 3-4-5 triangle ratio in the channels, so it can be shrunk to make a narrower, shorter air passage. Do you wish to manufacture vents? A set of simple wooden or sheet metal templates and jigs can speed production tremendously while keeping equipment and investment to a minimum. Start in your garage.

Materials are simple and non-toxic: heavy black acid-free paper, cardboard, fabric, and wood glue. Look in art or office supply shops for the paper. North Americans, use this paper weight and size conversion chart. If large sheets are unavailable, glue small sheets together between folds in plan. Wood glue has high tack and quick drying time, easing assembly. School glue will work, too.

Read through instructions once while studying plans.

  1. materials (see plans for quantities)
    1. paper (for channels and walls)
      • black, acid-free bond, coverstock
      • available at art supply, stationery, and book shops. In Europe, common posterboard is often acid-free.
      • two posterboard-size sheets (500 x 650 minimum) per vent
      • weights
        • channel: 120–300gsm
        • wall: 180–400gsm
        • total: 350–600gsm
    2. cardboard, single layer, 3–4.2mm thick (for shell, unnecessary inside silencer)
    3. fabric: polar fleece, black, medium weight (for seal. Quality check: 10 layers of it in a stack should measure 30-35mm high)
  2. follow instructions in air > fabricate
  3. sub-assembly
    1. attach wall channels to walls
      1. referring to assembly and key, get a clear idea of how parts go together
      2. glue channel and wall joints in alphabetical order between question marked holes. Channels lie between dash-dotted lines.
      3. glue narrow part of flaps to top and bottom of walls. Wide part should fold slightly upward
      4. position middle channels against upwardly angled flaps of wall channels and glue in place
    2. glue joints of shell together with shell seals
  4. assemble core
    1. put inner and outer wall sub-assemblies together and glue outer top and bottom over inner top and bottom. Note how V-shaped cut-outs in inner wall butt up against middle channel of outer wall.
    2. glue 20mm wide flaps of outer wall to inner wall
  5. shell
    • when using shell, put core inside and attach fleece seal with glue. This is a 20mm wide double-layer strip of fleece that goes around the flaps of the face opening. Three sides of the seal attach to the shell flaps. The fourth side goes across the core. Double-layers overlap at corners.
    • when not in use, store core inside shell, taping up flap by edge opening. Cover exposed part of core with scrap piece of cardboard to protect core from being crushed.
  6. installation
    1. determine vent location - in blind, panel, or silencer - whether it will attach at edge or face opening - shell is unnecessary when installed inside silencer or other enclosure
      • vent should not touch window handles, locks, or frame
    2. mark slot with slot plan
      • the slot plan spaces slot correctly on most blinds and panels - face opening, 50 x 216, on blinds, panels, or outside silencer, with shell - edge opening, 63 x 216, inside silencer or other enclosure, without shell
    3. cut out slot
    4. position vent over slot and fit vent flaps through it
    5. when attaching to soft window covering like fabric, plastic sheeting, or cardboard, pull long flap snug, use back of table knife tip to crease the outside of it right where it passes through slot
    6. fold flap at crease and tape it to cover. Tape is removable for vent reuse in another configuration later if you like. Only glue it in place if you are certain of not moving it for years.
    7. repeat with other long flap, then with short flaps
    8. attach shell to cover with tape, glue, or screws going through cover, into wooden braces if cover is soft
    9. cover shell with foil and/or white paper to minimize warping by sun

plan: helix-s vent, assembly
plan: helix-s vent, channels
plan: helix-s vent, inner-wall
plan: helix-s vent, outer-wall
plan: helix-s vent, slot

Follow helix vent instructions above, adapting as necessary.

threshold vent

A bedroom door often has a gap at the bottom—the threshold—for ventilation. In mechanically ventilated dwellings, this gap allows air to flow out of the bedroom toward the dwelling’s return vent (or perhaps just a window). The threshold vent lets air out but no light in. Its design adapts to door thickness, the height of the gap between bottom of door and threshold, width of door, and width of vent necessary for sufficient airflow. It works if gap is 15-33mm.

If greater than 33mm, add cardboard or wood to the bottom of the door or build up threshold with boards. Or modify the design. If less than 15mm, you can trim the bottom of the door. Otherwise, or if bottom of door fits into a stepped threshold, this vent will not work. Somehow, air has to get out of the room without letting in light.

Block light that reaches the door from the outside as much as possible. For example, make a removable partition in the hallway, which can also darken the path between darkroom and bathroom. It’s a wooden frame a little wider than the hallway so it wedges in at an angle, with a fleece seal around the frame, filled with black plastic sheeting with helix vents as needed.

plan: threshold vent perspective
plan: threshold vent


  1. materials
    • paper, acid-free, 400-600gsm bond or coverstock (empty cereal and frozen pizza boxes work, too)
    • muslin fabric, black
    • fleece fabric, black
  2. follow instructions in air > fabricate
  3. blacken inside of ends (grey area) with marker
  4. cut fabric to cover:
    1. area of bottom of door surrounded by vent + 30mm above each side (180–2h x w)
    2. threshold (t+40 x width of threshold+40)
    3. inside of vent except ends (t+200 x w+5; area between corners p, q, r, s)
    4. underside of vent + 10mm all the way around (t+60 x w+20)
  5. attach fabric
    • with tape to door and threshold
    • with glue to vent
  6. fold up ends to make a box-like structure, as in threshold perspective drawing
  7. tape flaps to outside of vent body (this can be undone later to store vent flat)
  8. tape vent to door at the triangular flaps
  9. fill in gaps on each side of vent with fleece baffle, as in drawing. Fleece measurement formula: 20+2h+t/2 x width of gap+10. Use 2 layers. Horizontal edge of fleece should be 10mm above bottom of door. If it drags out of position, weight it with a stick inside, half the thickness of the door. It is 5mm extra wide on each side to seal against the vent and the door jam. Cut away any fleece that interferes with door seal (see below).



Noise is another form of pollution a darkroom must provide shelter from. Noise comes from outside from machines, traffic—including big boats and airplanes—construction, music, fireworks, and talking and playing people. It comes from inside from other people in adjoining spaces, machines—refrigerators, fans, water pipes and pumps—music. At some point, noise defeats the retreat. It must be attenuated somehow, even in remote locations.

The four principles of soundproofing are clear and widely understood:

  1. mass: heavy materials absorb low-frequency (bass) sounds
  2. absorption: fine fibers absorb high frequencies and prevent echoing in air cavities
  3. dampening: using rubbery material to dampen vibration in resonant materials like metal, wood, masonry, glass
  4. decoupling: disconnect structures and airspaces to prevent transmission of sound vibration from source to receiver

Soundproofing tutorials abound online.

These principles apply to ventilation as well. Dampening and decoupling figure in fan mounting, and mass and absorption in silencer design. The silencer eliminates most noise, including from the fan.

Fans make noise directly and indirectly. Small fans have little hum to start with, but they run at high speed, so they develop a hum and harmonics. Bigger fans start with more of a hum but they run more slowly for the same air output, so they develop less noise overall. Avoid amplifying these vibrations by using the fan mount, below.

Even the quietest fan makes noise because of the friction of air itself against the fan blades, housing, ducting, and vents. Because of air friction, fully silencing a ventilation system requires a silencer of some type.


A silencer is an expanded duct section lined with insulation. Its greater volume depressurizes the airstream. This transforms low-frequency sound into into high-frequency sound. High-frequencies vibrate the fine fibers lining the silencer, transforming the sound into heat. Genius!

You can make or buy duct silencers.

  • my double-turn box design is below, $2-$10 depending on your material salvaging skills.
  • DIY straight tube design
  • acoustic ducting, at least 3m with 2-3 bends
  • silencer for sound booths. With dark insulation and enough bends, this eliminates the need for a lightproof vent.
  • manufactured silencers are made of metal and super durable materials and cost $100-200.

In the past year, I built two box silencers into window recesses. They were simpler and much more effective than I hoped. They swallowed up sound. One of two window panes formed one face of the box. The window recess in the thick wall provided the 4 sides. Boards formed the box’s outer face against the inside of security bars, about 20cm from the glass. I bought shredded fabric insulation to line it. See
darkness > window > hard panel section for more about adapting the design below.

Thanks to Richard Nöjd of Skattungbyn, Sweden, for finding these cool solutions. Silencers and acoustic ducting are standard industrial components, making buildings quiet worldwide.

plan: silencer


The plan is straightforward. It is just a wooden box with two baffles (internal half walls). The resulting zig-zag channel has a hole at each end. Each hole has 4 possible locations: faces, side, or end. Cut a circle for ducting or fan, a slot for a helix vent. The fan mount adapts to all 4 locations.

The box is lined with porous non-toxic insulation. Pillow filling, quilt batting, cellulose, clean wool, shredded fabric, wood fiber could all work. Note, the shredded fabric and wood fiber I’ve tried had faint smells that I disliked. I feel hesitant to use acoustic foam because I don’t know what chemicals are in it. Fiberglass and rockwool are unpleasant to work with and fiberglass often smells of chemicals. Closed cell foam like styrofoam, polyisocyanurate boards, camping pads, etc, is not porous so will not work.

Discarded furniture is made of melamine, an excellent material for silencer boxes. It is particle board with plastic veneer, usually 15 or 19mm thick. Marine plywood uses non-toxic glue. Otherwise, avoid plywood or line with aluminum foil.

Use a table saw to cut the 8 pieces so they come out square. Or have a carpenter do it for you, including the holes. Just take the drawing with you, modified for your needs. The carpenter probably has some extra melamine laying around to sell you cheap. To screw pieces together, first drill pilot holes so edges don’t break. I always drill pilot holes in wood less than 30mm wide for this reason.

To insulate, make square tubes of metal screen covered in porous fabric to form the channel. Stuff insulation around it and close the box. Or cut and glue sheet insulation in place. Roughen the plastic surface first with sandpaper so the glue sticks.



Use a case fan, also known as a squirrel cage fan. Specifications:

  • DC (direct current)
  • 12V (volts)
  • 120–360mm diameter
  • 600–1200RPM (revolutions per minute)
  • maximum 20dB (decibels)
  • 70-200cmh (cubic meters per hour) or 40-120cfm (cubic feet per minute)

120mm is the most common size, salvageable from a desktop computer tower, $1 at thrift stores or flea markets, or $2–20 at a computer or electronics store. Once you have experimented a bit, Noctua makes the best and quietest fans available, of 120, 140, and 200mm diameter, and as low as 7dB. Rexflo offers a 360mm jumbo fan. Avoid AC (alternating current) fans due to their penetrating hum (more on noise below).

Power it from the grid with an AC/DC universal adapter with pole switching and variable voltage for speed control ($5 at variety stores). Off grid, use car or household batteries or a solar power system. To control speed, use a 12V DC/DC car adapter from eBay. Attach one fan wire at each end of the pack. No fan movement? Switch the +/– poles on the adapter or switch the positive and negative wires.

More about an ideal fan, below.

fan mount

plan: fan mount


This mounting design totally dampens vibration from the fan. The silencer then absorbs the fan’s airborne noise. It is inspired by studio microphones and tensegrity structures. The resulting module fits over any hole in the silencer.

The design is fairly self-explanatory:

  • description
    • a fan held in mid-air by a web of 4 concentric rings of rubber sprung by 4 sticks in the web’s middle, hung on screw posts anchored in a wood base
    • modular, fitting on or in silencer in any configuration
  • materials
    • base: 20 x 240 x 240 (center hole, 120 diameter). I suggest having a carpenter cut this for you to get a precisely round hole.
    • case fan: 120mm
    • screws: 4@5 x 50 machine + 8 nuts, 16 washers
    • wood sticks: 4@3 x 10 x 154
    • rubber: (from bicycle inner tube) 4 strips, 1.5–2 thick, 15 wide. Lengths: 1@500, 2@660, 1@820
    • tie: wire, twist ties, zip ties, staples, or string
    • base-fan gap: 0.5–1
  • assembly
    • overlap ends of each rubber strip into rings by 20mm and stapled once at first, 4 times after getting the lengths right. They should be barely stretched, just taut enough to suspend the fan.
    • ties: connect each ring to the next
    • trim rubber to 12mm width at screws
    • align fan directly over the hole in base. Gravity may pull it to one side or another. Tug on webbing to reposition it.
    • adjust base-fan gap with nuts and washers and tugging webbing.
    • screw base onto silencer over a hole in any position
    • keep wires clear of outer 3 rings to prevent them from transmitting vibration.

In my first major darkroom in Guatemala, I had no electricity. I survived on foraged fruit and meals with my friends, Josh and Nadia, and would spend my last quetzal (worth $0.12) on darkroom building materials. At first, to create a draft, I actually made lamps that burned cooking oil inside a lightproof chimney. It was a messy, unreliable, and labor-intensive process no one should ever repeat. But it worked long enough for my brain to make the leap to the 20th century and remember the existence of batteries.

AA batteries made a quick and dirty solution. One night requires 4-8 batteries, alkaline or rechargeable. Connect them in series: positive end of one to negative end of the next. Each battery is 1.5V, so 4 batteries=6V. Some fans need 7V or 9V to start, thus 5 or 6 batteries. Increase fan speed by adding batteries to the pack, up to 8. Increase pack life by using bigger batteries or another series in parallel (fan wires contacting ends of both series).

I was isolated and just learning. This simple discovery encouraged me after weeks of the absurdity of oil lamp-driven convective ventilation. However, changing batteries every day also quickly got to be a pain. So I bit the bullet and got a proper solar power system for less than $100:

  • solar panel: 12V. Size depends on location: 10W in Guatemala, 40W in rainy Oregon winter. ($10–$100 on eBay)
  • charge controller: 12V, 4 or 6-pole ($35 on eBay)
  • battery: 12V 7A, lead acid ($30 at a motorcycle shop)
  • wire, 20 AWG, enough to connect everything ($0–10 from your shed, a dumpster, yard sale, or hardware store).

Once built, maintain by wiping dust off panel once a week. What a luxury! Of course, if you have reliable wind or hydro power, that’s great.


For heat, I often use a portable oil-filled heater. It is silent and can be positioned by a window or vent to warm incoming cold fresh air. Before buying, check that its indicator lights are easy to cover (not glowing from the interior through multiple cracks) and that it doesn’t rattle or hum. Old or cheap ones often do.

If you live in a cold place, I highly recommend buying and installing a Heat Recovery Ventilator (HRV) for both health and economy. It conducts heat from return air to supply air while keeping airstreams separate using an exchanging core and fans.

Fine wire heat exchange (fiwihex) technology is my favorite. It is 15x more efficient than conventional plate exchangers. Fiwihex cores have been available for $150 from Viking House and
Vision4Energy and possibly Fresh-R. These companies’ Breathing Windows embody an intriguing design for a complete ventilation system. But I lived with one for six months and found it too loud due to its small, high-RPM fans with integrated motors and no silencing. Thus my thinking about silent fans (more below).

The most interesting plate exchangers use the Mitsubishi Lossnay core, found in Energy Recovery Ventilators such as Renewaire’s. Made of high-tech paper, the Lossnay recovers heated water vapor as well as heat from air. Lossnay’s principle has DIY-potential, using 25m2 of non-siliconized parchment paper (“sandwich paper” in supermarkets). I have conceived a design for it. Please write me for details.

fan idea

A heat recovery ventilator requires two fans. The only trouble with case fans is that they are axial fans. These do not efficiently generate enough pressure to overcome the resistance in ventilation systems (long pipes, heat exchanging cores, filters, convoluted vents). But centrifugal fans can. These are pricey, starting around $50, and usually AC powered, so they hum. DC or EC (Electronically Commutated) centrifugal fans cost even more.

It would be nice to have cheap, quiet fans for this: large, low RPM homemade centrifugal fans with DC motors outside the airstream in a separate, soundproofed case. In late 2016, I prototyped a 50cm diameter fan from wood, cardboard, paper, and steel (photos upon request). The AC motor I salvaged from a discarded fan taught me the hard way about AC hum. The rubber inner tube motor mount and foam driveshaft did not fully decouple and dampen it. And air friction in the fan across the blades caused a surprising amount of noise. Each airstream would require a silencer. But this design ought to totally eliminate fan noise while producing high volume. The fan’s parts could be metal or plastic and lasercut according to an open-source, electronic plan file.


In some cases, an air purifier becomes necessary. If your house is near a factory, busy roads, in a smoggy city, or near a smelly restaurant or neighbor, get one. The main types I have heard of are HEPA filtering, ionizing, and ozonating purifiers. I have never used one and it requires more research, but it could be integrated with your ventilation system. For example, I have seen ionizing units small enough to fit inside the silencer. If air quality at your home is bad enough, consider moving. There’s lots of space left in the countryside and it doesn’t have to be costly or complicated.


That’s it for ventilation, silence, power, heat, and purification. On to lightproofing doors and windows.

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