7 - 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.

Ventilation also affects silence and 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, pentillions 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. Along with not freezing to death and being safe from injury, we have no greater concern in life than arranging to breathe fresh air continuously and comfortably.


  • provides plenty of fresh air
  • 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){threshold vent specifications in curly braces}:

  • durable (protective cardboard shell){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}
  • short airway (260mm){140mm}
  • minimal size (80 x 265 x 280){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

photo: helix vent core, exploded

plan: helix vent, assembly

plan: helix vent, channels

plan: helix vent, inner wall

plan: helix vent, outer wall

plan: helix vent, shell

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 its face opening poke through a 40 x 282mm slot and fold down with tape or glue.

  • window: 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 vent (leading outside or to another room): attach vent to a cardboard box and attach box to the wall over the vent. Vents can be either supply or return vents; air flows either direction through the vent.

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 or wish to manufacture vents? I prototyped some based on the same helix principle that proved too difficult to make by hand. Write me for photos, plans, and instructions. It is 280H x 180W x 60D (where W is distance through vent). Further reductions are possible (down to W of 65) for compact applications.

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 or coverstock
      • available at art supply and fine stationery and book shops
      • weights
        • channel: 120-300gsm
        • wall: 200–400gsm
        • total: 390–600gsm
    2. cardboard, single layer, 3–4.2mm thick (for shell)
    3. fabric, polar fleece, black, medium weight (for gaskets; 10 layers of it in a stack should measure 30-35mm high)
  2. follow instructions in basics section above
  3. sub-assembly
    1. attach channels and gaskets to walls
      1. referring to key, get a clear idea of how parts go together
      2. glue channel and wall joints in alphabetical order
      3. glue gasket inside top and bottom of outer wall
    2. glue joints of shell together with shell seals
  4. assemble core
    1. glue 20mm wide flaps of inner wall to outer wall
    2. glue 20mm wide flaps of outer wall to inner wall
  5. if not using immediately, store core inside shell, covering exposed part of core with scrap piece of cardboard to prevent crushing.
  6. installation
    1. determine vent location in panel
      • edge opening of vent should face window opening
      • vent should not touch window handles, locks, and frame
    2. on panel, mark slot exactly the size of the vent’s face opening, 40mm x 282mm
    3. cut out slot
    4. from the back, position vent core over hole and fit vent flaps through it
    5. lay panel on table, core down and panel up
    6. pulling top flap up snugly, use back of table knife tip to crease the outside of it right where it passes through hole
    7. fold flap at crease and glue or tape it to front of panel
    8. repeat with bottom flap, then with side flaps
    9. attach shell to back of panel over core with tape, glue, or screws going through panel into braces
    10. cover shell with foil and/or white paper to minimize warping by sun

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 basics section
  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.
  • standard silencers are made of metal and super durable materials and cost $100-200.

In the past year, I built two box silencers into window openings. They were simpler and much more effective than I hoped. They swallowed up sound. The window pane formed one face of the box. The window opening provided the 4 sides. Boards formed the box’s other face, covering the window on the outside, against the inside of the 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 internal half walls. The resulting 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 rectangle for a doubled helix vent, or a slot in end for helix vent. The fan mount is adaptable to all 4 locations.

The box is lined with porous insulation. Acoustic foam, shredded fabric, wood fiber, cellulose, fiberglass, or rockwool (mineral fiber, much like fiberglass), quilt batting and pillow filling all work. The fabric and wood fiber I’ve tried had faint smells I disliked. I feel hesitant to use acoustic foam and fiberglass because I don’t know what chemicals are in them. Cellulose, quilt batting, pillow filling, and rockwool seem neutral. Like fiberglass, rockwool is unpleasant to work with but stable once installed. Do not use closed cell foam like styrofoam, polyisocyanurate boards, camping pads, etc, as these do not conform to the silencer principle.

Discarded furniture is made of an excellent material for silencer boxes called melamine: particle board with plastic veneer, usually 19mm thick. Use a table saw to cut the 8 pieces so they come out square. Or have a carpenter do it for you, maybe 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.

Glue insulation in place. Roughen the plastic surface first with sandpaper so glue sticks. For rockwool, use screws and large plastic washers cut from bottles. For cellulose, make tubes of metal screen covered in porous fabric to form the cavity. Stuff the cellulose around it and close the box.



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 mount greatly dampens vibration from the fan. The silencer can then absorb 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
    • 4 concentric rings of 1.5-2mm rubber make a web that holds the fan in mid-air
      • ring touching the fan is wide: 15mm
      • other 3 rings are narrow: 3mm
      • 4 wooden sticks with notches cut in the ends are suspended in the middle of the web to make the two outer rings possible in such a small space.
  • materials
    • base: 19 x 240 x 240 (hole 120 diameter)
    • fan: 20 x 120 x 120
    • base-fan gap: 3
    • screws: 5 x 50 machine, 12 nuts and washers
    • spacers: 5 ID (inner diameter) x 9-15 OD x 3 (2 of each size); rubber, plastic, wood, or metal
    • wood: 3 x 10 x 160 (notch at 158)
    • rubber: 1.5 thick, 3 wide (15 on fan body)
    • tie: wire, twist ties, zip ties, or string
  • assembly
    • align fan directly over the hole in base. Gravity may pull it to one side or another. Use 1-3 spacers of rubber tubing or wood over the screws with washers to adjust fan position.
    • Adjust base-fan gap with nuts and washers. It prevents transmission of vibration to the resonant base. But it also makes the fan less efficient due to air pressure drop. This could be sealed with plastic film, loosely applied or a bit of fleece. The next iteration of the design will provide a tested way to seal this gap without transmitting vibration.
    • ties: thin wire, twist ties, zip ties, or just string that connects each ring to the next.
    • In wide ring, make 2 holes or slits 3mm apart on either side of narrow ring where they connect. Tie them together through holes.
    • screw module onto silencer over hole in any position
    • keep wires clear of outer 3 rings to prevent them from transmitting vibration.
    • design is new. Send complaints and suggestions. Check back for new prototypes.


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. Air friction in the fan caused a surprising amount of noise. Each airstream would require a silencer. But this design ought to totally eliminate fan noise. The fan’s parts could be metal or plastic and lasercut according to an open-source, electronic plan file.


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

<   ^   >