Installing air conditioning? Choose the right scaffold.

The Altrex Mi Tower is the most practical model for this work: 75 cm wide, built for one person and good for up to 6.2 metres of working height. For an outdoor unit on the first floor you sit comfortably inside that. It is light enough to put up alone and narrow enough to reach the wall down a drive or a side path. Which builds exist is set out on the page about the MiTower and its heights.

On the deck there is room for everything this job brings with it: a core drill, a hammer drill, a spirit level, brackets and a box of bolts. What does not fit is a second pair of hands, because this build is rated for one person. If two of you have to lift the outdoor unit onto the brackets, hire a mobile scaffold with a longer deck instead, such as the RS51 at 75 cm from the same range of towers.

If the unit hangs higher than the first floor, or a heavy model arrives with a second engineer, the wide RS52 at 135 cm is the logical step. On that deck you can set the appliance down for a moment before it goes onto the brackets, and with a heavy unit that saves a lot of lifting. For an ordinary wall unit at four metres it is overkill, and there the narrow build mainly buys you speed.

Work out first where the top bracket will sit, because that is your highest working point and not the roof edge. For an outdoor unit under a first floor window that is usually around three metres, which puts you exactly right on 4.2 to 5.2 metres of working height. Working height here counts as the height of the deck you stand on plus the roughly 2 metres you reach with a stretched arm. Your platform therefore ends up around two to three metres.

Measure from the level where the wheels will land, and not from the threshold of the front door. Standing on a sunken patio or a drive that falls towards the street shifts the whole sum. If the unit hangs above an extension or a bay, you have to stay further from the wall and need extra height to get at it at all. Compare your own situation on the page about five metres of working height.

Hiring too low shows up the moment you drill. A core hole is made with both hands and your body weight behind it, and that fails if you are working above your head. Levelling the brackets goes inaccurate as soon as you have to reach. Caught between two builds, take the higher one: half a metre too much you never notice, half a metre too little you feel all day. How high a wall point sits on that floor is at the height of a first floor.

The tower goes straight under the spot where the outdoor unit will hang, and that spot follows from the pipe route inside. So measure indoors first to find where the duct comes out, and only then fix the standing position. Under an outdoor unit you usually find a patio, a drive or a strip of gravel along the house. Slabs and tarmac are fine, while loose gravel and fresh soil ask for levelling plates under the wheels before you climb.

Around the base there has to be room for the four stabilisers, which splay outwards and take more space on every side than the build itself. At a house that is exactly where the outside tap, the drain, a bike rack or the bins usually stand. Clear it before delivery. Think too about where the appliance waits before it goes up, since you want it close to the tower and not at the back of the garage, because every metre carried with thirty kilos counts.

If the wall stands close to the boundary, part of your setup hangs over the neighbours' path. Mention it in advance, especially because core drilling makes a lot of noise and dust and can keep you busy for half a day. Check as well that the unit can blow out freely later without facing a fence, or you will be moving it after all. How to get a setup firm is explained in the piece on stabilising.

The fitting itself is a day's work at most. Marking brackets, drilling the core hole, sealing the duct, hanging the unit and tidying the pipes fits into a morning and an afternoon at most houses, from one position you never move. Even so you rarely hire the tower for a single day. You want it standing before you start and only taken away once you are sure nobody needs to reach the appliance again, and that alone pushes you towards two days.

The real planning sits with the installer. Connecting and vacuuming the refrigerant is an engineer's job, and he comes at his own moment. Until that visit has happened you have to be able to reach the outdoor unit. So ask for his date first and set your rental period around it, with a day of slack on either side. Then nobody waits and you build nothing twice, because a tower already gone when the engineer rings costs you a second hire.

That slack costs you almost nothing. Only the opening twenty four hours are charged in full, and each following day joins the total with 95% off, so three days differs little from one. For a job that hangs on somebody else's diary that is exactly the room you need to keep. Put your collection date a day or two behind the appointment. How to judge such a period is explained in the piece on rental days.

With air conditioning you barely move the tower. You set it down once, straight under the brackets, and finish the whole job there. That is precisely why the position matters so much, because half a metre too far left and you drill crooked or have to reach. So mark the bracket holes from the deck first, check that you can get at both ends comfortably, and adjust the spot before you drill for the first time.

Plan what goes up in one trip. Core drill, extension lead, hammer drill, spirit level, brackets, bolts and sealant come up with you, but the outdoor unit itself does not go up in your hands. That appliance you haul up on a rope or pass up with two people, because climbing a ladder or a stair with thirty kilos goes wrong. Lay a cloth on the deck so bolts and drill bits cannot drop between the platform sections.

The duct is the moment you understand why a ladder is no good. A core hole is drilled sloping slightly outwards with your weight behind the machine, and that asks for firm footing. The same goes for pushing the pipes through, fitting the sleeve and sealing the duct, all of them things where you cannot hold on. If you are also fitting a ventilation grille or outlet that week, plan it inside the same rental period.

What comes off the van is a set of loose parts, complete and counted beforehand. Pick a place for that stack in advance, because the drive or the front garden works better than the patio, where you will be standing with the appliance. Anything confirmed on a working day before 15:00 is at your address the next working day, so you can still decide late if your installer's date has only just been settled.

When the set arrives and when it leaves is your call. For this job you put delivery a day before your drilling, so you can build calmly without the engineer already at the door. Building is your work: the manual and the instruction video take you through it, and a one person build goes up fine alone. Allow half an hour before you can start marking. Run through the step by step build guide first.

Collection is ours, dismantling is yours. Put the parts together afterwards somewhere the van can get to them easily. Wait until the installer has finished his work, because otherwise the unit hangs loose on the wall with nobody able to reach it. Tick off the parts while you dismantle, so nothing has to be searched for on the last morning. Which amount applies to the run out and back depends on your province, and you find it under the delivery charges.

Standard EN 1004 sorts scaffolds into load classes, and our builds sit in class 3, which allows 200 kg on every square metre of deck. On this job that is not a theoretical figure, because an outdoor unit soon weighs thirty kilos, and then you, a core drill and a box of bolts come on top. Put heavy material in the middle of the deck rather than all against one guardrail. What the classes mean is in the article about this standard.

Brake the wheels as soon as you step on and never move the build while tools or a person are on it. Drilling asks for sideways force, so check before you start that all four stabilisers stand firm. Stop in strong wind, because an outdoor unit is a large flat plate that works like a sail while you are hoisting it. A half full tool bag swinging from the guardrail comes off then too, along with everything loose on the deck.

If you are working alone, arrange for somebody to be nearby. On this job you stand still in one place for a long time with both hands busy, and that is exactly when something drops: a core bit, a bolt, a length of pipe. Keep the zone under the tower clear, put a bucket there as a marker, and sweep drilling dust off the deck, because grit makes the floor treacherous. The other rules are on the page about working safely at height.