Installing multipoint air conditioning (2)

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This is a project to separate the heating of the smaller upstairs bedrooms from the much larger downstairs living areas in a 6-bedroom detached house


A two-storey detached family house. Built in 1968, it has had roof insulation top-up and cavity fluff injection, but it is stil a big place to heat. There's no mains gas, the current central heating is from a Potterton Statesman 28kW oil-fired system boiler in an outhouse, actually a tiny lobby attached to the kitchen. The system is a standard 1960's design with separate water tanks in the loft for DHW and the CH radiators, a large hot water cylinder in the upstairs airing cupboard, a 3-way diverter valve and a programmer-timer for a 7-day cycle.

The kitchen sink never got hot water really. and nobody uses the bath, it's in a large cold room. Three power showers have been added as en-suite additions anyway. But two of the showers have pumps designed for a gravity-fed system so I can't remove the DHW tank and header without a lot of problems.

The living area is vast, open-plan, with big floor-to-ceiling windows in the style of that time. It needs four large radiators to heat it. There's a large kitchen, underheated, a dining room that is never used and a parlour, also never used. We congregate in the big room mostly or the kitchen. Upstairs is cold unless the ground floor is heated, so the boiler is on all night and day. All bedrooms except one are singles with small radiators.

On first look, it seems I can't improve on the existing system except by upgrading the old boiler. The insulation is already maxed, short of adding thermal roller shutters to the windows. So we will have to economise in other ways to reduce the heating bills.

So a life-style change is needed. Actually it already happened naturally. Al I need to do is change the heating system to meet it. The family is grouped in the big room mostly, bedrooms are only for sleeping, too cold to use as teenage study bed-sit rooms, too small too. So I decided to separate the house into day-night sections and provide separate heating for the bedrooms, then turn off the boiler at night. Early morning it will heat the DHW tank to run three showers for eight people, then heat the living area until nearly bed-time. That will also curtail very late night roaming, imposing a routine on the household.

With the boiler off at night, I need independent heating for six bedrooms. I decided to use two 3-unit air to air multipoint air conditioner systems and that 2kW per room was enough. Any more heat could be either emergency boiler firing or an electric portable heater, like a small oil-filled one. This would be useful during sick-room occupation or very cold snaps. I matched the three 2kW fan units with a 5-6kW compressor heat pump. With the piping and electrics run as a DIY project, the fitting costs including the two compressors, the six downflow heaters and VAT came to just over £1,000 per room. Not cheap, but not exorbitent.

DIY installing

compressor on wall bracket, duct on right to eaves

Two problems with air-con are eliminated here. In top floor bedrooms I can run pipes over the loft, up through the eaves and down through the ceilings, fit the internal units near an outside wall and run condensate pipes out directly to drip on the ground. In five of the six rooms I could fit units on internal walls in the angle next to an outside one, which made both the gas pipe and drain pipe easy drillings. The last room I had to run pipe around a window unfortunately. Doesn't look so neat. The pipes down from the ceilings I put on the left side of the units and covered in PVC duct.

The pipe runs outside from the roof eaves go down two ducts to the compressors which sit on special wall-brackets. I ran 2.5mm TWE cable spurs from two 10A MCBs added to the house consumer unit (actually I had to increase the size of that). Each spur was ducted via a rotary isolator switch which was mounted, as required, within 1m of the compressor. I marked up the pipes and cables with coloured tape for each room, then left the rest to the F-gas fitters. Took 2 man-days for him to braise up the pipes, flush with nitrogen, fill with refrigerant, pressure test and connect the cables.


Air-con pipes are imperial sized and certified for high pressures. There are suppliers in most areas, listed as refrigeration supplies. My system used 1/4 and 3/8 pipes, these covered by 9mm thick black foam insulation sleeve. You need a 24mm diameter drill for any through-holes. The control cables are light 4-core flexible, the power cables as normal house wiring for a running current of 5 amps. Surge current can be higher but the 10A MCBs seem to be OK. The only bits I had to order especially were the lengths of 120 x 75 duct from BES. I just managed to squeeze 6 wrapped pipes and 3 cables into that. I cut some 70mm square drain pipe in half to cover the inside pipes from the ceilings and foamed them onto the pipe insulation. I foamed the holes between the eaves and the ducts outside too, no gaps left for the wasps.


..... wait for Winter and see.

Air-con down-flows come with a TV-style remote control. You have only an on-off function, the off can be delayed in half-hour periods. You can set temperature, of course. If you set that fairly low, set the fan speed to minimum and leave it on all night the soft rustle of the fan can be quite soothing. Eventually you won't notice it. Best not to put it on automatic, it can decide to change fan speed and that will intrude for a light sleeper.

When you choose an installer, you get the manufacturer they are tied to. I don't think it matters whether it's Mitubishi, Daikin, Toshiba or whatever. I went for the nearest smaller business in my area who would accept a part-DIY job. The big energy companies wouldn't be interested unless they could lead and control the whole project. I just looked locally for refrigeration and air conditioning businesses.