A ducted dehumidifier sits in the ceiling or a plant room and serves several rooms through ducts, so you do not have a machine in each bedroom. The same drying idea works inside an air handling unit, or AHU, in a larger building. This page explains how an AHU dehumidifies, how a whole-house unit differs from air con dry mode, who designs it, and what drains, power and servicing it needs. Send one request and independent HVAC firms in your area quote you directly.
How dehumidification works in an AHU
In an AHU, air is cooled below its dew point as it passes over a cooling coil. Water condenses on the coil and runs to a drain. The air is then usually reheated, so it leaves dry and at a comfortable temperature rather than cold and damp.
A dedicated ducted or inline dehumidifier uses the same principle in a simpler package: it takes air from the house or from outside, dries it, and distributes it through ducts to several rooms. It suits larger homes, offices, pool halls and buildings where a portable unit would be in the way.
Air con dry mode or a dehumidifier
An air conditioner removes some moisture as it cools, and many have a dry mode. But it is designed to cool, not to hold a set humidity, and it does little in cool damp weather when there is no cooling load. Running it in winter to dry a room can feel cold and use a lot of power.
A dehumidifier holds a target humidity whatever the temperature, which is why it suits a damp Cape Town house in July. In some buildings both are combined: the air con handles temperature while a ducted unit controls humidity. See dehumidifiers for the basics.
Design, drains and power
A ducted system should be designed by an HVAC engineer or an experienced installer. They look at the building volume, the moisture load, where the ducts will run, and where the dry air should go. Poor duct design leaves rooms unevenly dried, and a unit placed too far from the damp room does little. Ask the installer to explain where each duct ends and why.
- Drain: a condensate drain falling to a gully, or a condensate pump where gravity will not do.
- Power: a dedicated supply installed by a registered electrician who issues a certificate of compliance (CoC).
- Access: space and a hatch for filter changes and servicing.
- Controls: a humidistat in the main living area, and a way to override it.
Servicing and when it makes sense
Filters need cleaning or replacing, coils need cleaning, and drains and pumps need checking so they do not block and leak into the ceiling. Refrigerant work must be done by a technician registered for it. Ask about a service plan when you get the quote.
A ducted system costs more than a portable unit, so it makes sense when the damp is permanent, the house is large, or several rooms need drying at once. For smaller jobs see home dehumidifiers, and for fitting details dehumidifier installation.
What to put in your request
- Floor area, number of rooms and ceiling height
- Where the damp is and how long it has been a problem
- Space for the unit: ceiling void, plant room or roof
- Whether an air conditioning system already exists
- Your town, and when you would like the survey
Ducted and Whole-House Dehumidifiers for homes, rentals, businesses and industry
- Homeowners and tenants: dries several rooms at once in a larger house, with no machine to empty or move around
- Landlords, agents and body corporates: controls humidity across a block's common areas, basements and a row of similar flats
- Offices, schools and clinics: adds humidity control to the air handling unit that serves an office floor or a clinic
- Warehouses, archives and storage: dries a records store or a chilled area through its existing ducted air supply
- Factories and food plants: controls humidity in a clean room, a packing hall or a process area through the AHU
- Growers, nurseries and farms: serves a propagation room or a drying hall with a ducted unit and a steady target
- Hotels, gyms, spas and pools: dries a hotel wing, a spa or an indoor pool hall through a ducted dehumidifier
- Insurers, assessors and restoration firms: adds drying capacity through an existing duct system in a building affected by damp
- Builders, HVAC engineers and contractors: specifies and installs the unit, ducts, drain and electrical supply for a new build
Frequently asked questions
Do you sell or install dehumidifiers yourselves?
No. We are a free quote request service. We pass your request to independent suppliers and HVAC contractors who work in your area, and they quote you directly.
Is a whole-house dehumidifier worth it?
It can be, in a larger home with permanent damp or several affected rooms. For one damp bedroom, a portable unit is usually cheaper and simpler.
Can my air conditioner replace a dehumidifier?
Partly in warm, humid weather, through its dry mode. In cool damp weather it does little and is not built to hold a set humidity, so a dedicated dehumidifier works better.
Who designs a ducted system?
An HVAC engineer or an experienced installer, working from the building volume, the moisture load and the duct route. Ask what is included in the quote: design, drain, electrical work and commissioning.
Ducted and Whole-House Dehumidifiers by province and city
- Johannesburg
- Pretoria
- Centurion
- Midrand
- Sandton
- Randburg
- Roodepoort
- Krugersdorp
- Randfontein
- Germiston
- Boksburg
- Benoni
- Kempton Park
- Alberton
- Vanderbijlpark
- Vereeniging
- Durban
- Pinetown
- Pietermaritzburg
- Richards Bay
- Newcastle
- Ladysmith
- Gqeberha (Port Elizabeth)
- East London
- Kariega (Uitenhage)
- Mthatha
- Cape Town
- Bellville
- Paarl
- Stellenbosch
- George
- Worcester
- eMalahleni (Witbank)
- Middelburg
- Secunda
- Mbombela (Nelspruit)
- Rustenburg
- Brits
- Klerksdorp
- Potchefstroom
- Mahikeng
- Polokwane
- Tzaneen
- Kimberley
- Upington
- Bloemfontein
- Welkom
- Sasolburg