In short: what plant rooms need
Plant rooms in a house are designed around servicing, not around the size of the equipment. Each unit needs its manufacturer's service clearance, a route and a door wide enough to replace it whole, a floor drain, ventilation, light and a socket, and the noisy ones need distance from the bedrooms. All of this goes into the house layout before construction starts.
If the equipment only gets whatever space is left after the rooms, within a couple of years changing a filter means dismantling a cupboard, and replacing the hot water cylinder means taking a door off.
Which equipment lives where
A modern house near Barcelona has more kit than people expect. The outdoor and indoor units of an air-to-water heat pump and a 200 to 300 litre hot water cylinder. The main consumer unit and, with solar panels, an inverter and possibly a battery. The water main with a filter and, if the water is hard, a softener. A heat-recovery ventilation unit and its ducts. A data cabinet with the router and switch. And if there is a pool, the pump, filter, water treatment and chemicals.
Some of this can be grouped in a single plant room; some has to sit next to what it serves: pumps near the pool, the outdoor unit outside, the ventilation unit close to the middle of the duct network.
The catalogue size is not the whole story
The catalogue gives the size of the casing. The manufacturer's manual also gives service clearances: how many centimetres must be free in front, at the sides and above to open a panel, pull out a filter or change the cylinder's anode. Take those figures for every model chosen and draw them on the plan along with doors, furniture and circulation.
Check the replacement route as well. A cylinder about two metres tall has to get through the door and the corridor, and down the stairs if it lives in the basement. Someone will be carrying 25 kg bags of softener salt on a regular basis. Ventilation unit filters are changed several times a year, and if the unit is above a suspended ceiling, the hatch has to let you reach them, not be a token gesture.
Services for the room itself
A plant room needs a floor drain: discharge from the cylinder's safety valve, filter washing, condensate, breakdowns. It needs a water point, dedicated sockets, proper lighting rather than a single bulb, and ventilation so heat and moisture do not build up.
Pumps and compressors are noisy and they vibrate. Put them on anti-vibration mounts and do not place the plant room behind a bedroom wall. For the inverter and battery, the manufacturer sets a temperature range and installation conditions; a hot garage with a south-facing wall may not qualify. All of these requirements are established before the walls go up, not when the equipment is delivered.
Outdoor units and the pool plant room
The heat pump's outdoor unit needs free air intake and discharge, service access and a spot where its noise bothers neither you nor the neighbours. Under a bedroom window or right on the boundary with the next plot are poor choices. If you want it hidden, the screen must let air through, or the unit will recirculate its own exhaust.
The pool plant room goes close to the pool, often below water level so the pump does not draw in air. It needs a drain for backwashing the filter and a separate ventilated space for chemicals, which must not be stored next to electrics. How to plan the house, pool and garden together is covered in a separate article.
A cupboard should not hide the problem
Equipment can be built neatly into joinery: the boiler in a kitchen tall unit, the consumer unit in a hall cupboard, the router in a niche. On one condition: access remains what the manufacturer requires. Doors that lift off or open on hinges, not glued panels. Ventilation grilles not covered by decorative panels. No shelves inside that have to come out for servicing.
Before the concealing joinery is made, the equipment installer should confirm the access zones on the joiner's drawing. A handsome solution loses its point if you have to call the joiner every time the annual service comes round.
Information you will need years from now
When the house is handed over, put the equipment models and serial numbers, manuals, warranties, service schedule and installers' contacts in one folder. Label valves, breakers and circuits. Keep the photos of the services taken before the walls were closed, with dimensions for reference.
The house with a pool and solar panels that we delivered end to end between 2022 and 2024 has more equipment than usual: pool plant, the inverter, heating and hot water. The more kit there is, the more it matters that in five years a new service engineer can understand the system in half an hour rather than a day.