A split does not ventilate a darkroom and it does not handle chemistry. Extraction of fixer, developer and any other process air is a separate system, designed for that process. Comfort cooling is only worth adding if the process instructions allow the room temperature you want. Do not guess a chemical temperature from a remote. If the process needs a stated condition, follow the process instructions and accept that a comfort split may be the wrong tool. This page is installation, not a darkroom method.
The coil does not capture vapour at the tray
The air conditioner recirculates room air across a coil and rejects heat outside. It does not capture vapour at the tray and send it outdoors. A fan that blows over open trays can spread smell and can land condensate where you do not want liquid. Keep the indoor unit out of the wet bench zone.
No split standing in for a missing extract
If there is no proper extract, do not buy a split as a substitute. Sort ventilation first, with someone who understands the process. Then ask whether a comfort unit can share the room without fighting that extract or upsetting the temperature the process needs. A portable still does not extract chemicals, and the hose plus a blackout is awkward. It is not a safer chemistry solution. It is a noisier comfort stopgap.
A loft that overheats between short sessions
Some rooms are used for short sessions and the process is tolerant of ordinary room temperatures. A small split can then take the edge off a loft darkroom that overheats. Confirm that tolerance from the process instructions, not from an installer. The installer can hold a setpoint. They cannot validate chemistry. If the process instructions do not allow a comfort setpoint, do not add the split. It might spoil the process if you undercut a temperature the process depends on.
Blackout, a trusted drain, lights down
Blackout and a closed door are already how the room works. That suits a split, which wants windows closed while it runs. The drain must not drip into trays or onto paper. A pump failure in a blacked-out room is easy to miss. Prefer a drain you can trust, and an isolator you can find with the lights down.
- Extraction is separate from the split.
- Comfort cooling only if the process allows it.
- Keep the indoor unit off the wet bench.
Filter access in the dark layout you use
Darkrooms are often box rooms or loft cupboards. The indoor unit needs filter access in the dark layout you actually use, not in a showroom plan. A tiny room with a huge unit will overcool and ice if someone sets 16C. Ask for a small kilowatt rating. Do not take a setpoint from a guess, and do not send chemical names expecting one in return.
Condenser air stays out of the light-trap
The outdoor unit stays outdoors. Do not blow condenser air into a light-trap. F-gas rules apply. In England, Planning Portal conditions apply to the outdoor unit on a house. A windowless room does not create an exemption. A competent installer should refuse the job if the only result would be air across open trays.
Frequently asked questions
Can a split extract darkroom fumes?
No. It recirculates. Chemical extraction is a different system. Fit that properly before you talk about comfort cooling.
Core buying guides
Start with these high-intent guides, then dig into the rest of the library.
Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.