First-fix plumbing is essentially the pipework for space heating, water supply and waste water drainage. It could take place simultaneously with the electrical installation were it not for the fact that plumbers need space to work in and it is best to give them that space unencumbered by other trades.
As with other trades, plumbing that appears neat and tidy when installed, is usually the sign of a good tradesman – somebody who has given due care and attention to planning the layout and implemented that plan carefully, without damaging previous trades’ work under the dubious heading of ‘making good.’
Second- fix plumbing is the connection of the appliances, their testing and commissioning. Appliances include bathroom sanitaryware and radiators, as well as boilers and other equipment.
Some additional considerations come with today’s gas and oil-fired condensing boilers.
Firstly, they have to be connected to the drains so the condensate can be removed. The small plastic pipe that carries the condensate away can be plumbed into the waste pipe under the sink but it can equally connect to a pipe outside the wall – just don’t allow your plumber to run it too far around the house as they don’t look pretty.
If no drains are nearby a mini soakaway can be used instead. The condensate isn’t quite as pure as you might think, it contains some acid, and so the pre-formed soakaways contain a carbon filter to neutralise it.
For most boilers the flue can be extended vertically or horizontally or a mixture of both to find a suitable outlet position. Distances of maybe five metres for the flue length aren’t unusual and so the boiler itself doesn’t even have to be located on an outside wall.
The flue does have to have its outlet in fresh air however, and in fact it is the flue terminal that often decides where the boiler will be sited.
It has never been easy finding the right spot to exhaust boiler flue gases, as they can’t discharge beneath windows, under roofs, in corners, near extractor fan vents or close to boundaries.
The new generation of electric boilers avoid these problems but can have a big negative effect on energy efficiency if they aren’t backed up by solar panels, which pre-heat the supply.
Underfloor heating uses the floor itself as a radiator, avoiding the need to hang steel panels on the walls.
Because it is larger than conventional radiators it can be heated to a lower temperature to achieve the same result. You can always add bathroom towel warming radiators to the system if you want.
Save time and effort by choosing one with a grid-like retaining system that allows the pipes to be ‘walked’ into position and held there.
Most of the work in laying under-floor heating comes from pinning the snake like pipe into position over the insulation. What appears as a network of plastic (polybutylene) pipes, is in fact just one pipe looping in a circuit, flexible enough to bend to the radii of the support clips and long enough to serve a large room.
The reliability of these systems comes from the fact that they are jointless – when they are buried beneath the floor finishings this is essential.
Do not allow the pipe to be cut and jointed on site; the guarantee is likely to be discarded.
Storing hot water under pressure is the preferred option today since you can run more showers and have it delivered at mains pressure to the taps in a sealed system.
Unvented cylinders can run a mixer shower with some pressure, something a combi boiler can’t do. Most homes will need one of the large floor standing units up to 500 litres. They can be heated by electricity, gas or oil-fired boiler.
The electric options save space but are not economical, unless you can heat the store up at night on cheap-rate power. Because the water is stored as high as 80°C inside, a lot of insulation is needed and frankly the factory fitted lagging isn’t always enough.
Some cylinders fitted into a cupboard in a bedroom give off so much heat they can make it impossible to sleep.
Check that the hot supply pipes are insulated to prevent heat loss within one metre of any hot water store, something plumbers often forget to do.
The plumbing required is dramatically reduced if you choose an unvented system as no loft tanks are required, just space enough for what is usually a very large cylinder with an expansion vessel.
Whether you use copper or plastic pipes, it pays to have some extra fittings installed at the first-fix stage to make maintenance easier and enhance performance.
Fit quarter-turn service valves on both hold and cold supplies to appliances.
Install a magnetic type boiler filter to any radiator heating system to prevent sludge build-up blocking your boiler.
Fit flow limiter valves before an appliance to balance the flow and guard against static pressure build ups. It is critical to have any mixer showers balanced correctly.
Quite often the pressure differences between cold water and hot water arriving in the valve are extreme, causing them not only to fail to deliver water at the correct temperature but also to backflow through the valve. Fit double check valves to prevent backflow to the boiler and contamination of the water supply.
Above ground drainage systems have never been easier to install. They’ve even made that task easier with the advent of push-fit plumbing to complement the traditional solvent-weld (glued joint) and compression (screwed joint) fittings.
All that is required is a workable plan and a basic understanding of the things that you can’t do, but do make use of the catalogue of parts provided by plastic drainage manufacturers.
Of the three waste pipe plumbing systems on offer, solvent-weld is the most durable. As a glued system, make sure everything is push fitted together first, then take it apart one joint at a time and glue it back together.
Do not be tempted to glue it up on your first attempt because the weld doesn’t come apart after it has set, at least not without a saw. If you have any runs that are going to be concealed or inaccessible once the work is all finished, then use solvent weld.
Compression joints are more forgiving, since they can be made and unmade repeatedly until you get it right. They are easily removed and refitted by threaded nuts. No glues or tools are required. But unless the joints are tightened and the chamfered rubber seals are correctly seated (not pinched or miss-shaped) they will leak sooner or later.
The push fit system isn’t compatible with solvent-weld pipes because of this reduced diameter. It may be only minor but it’s enough to prevent you joining the two.
Push fit pipes can be kinked because of this and this lack of strength must mean they need plenty of support if hot wastewater is to be flowing through them without causing the pipe to sag.
Three checks to make on your waste water plumbing:
Waste pipes have limits if they are to remain ventilated and the water maintained in the traps. If they exceed these limits, added vents are needed at the branches or air-admittance valves (AAV’s) installed that can draw air in on demand to compensate.
AAV’s draw air into the system when it’s needed to aid the flow of water and protect the traps but they can only be installed internally (including roof spaces) and must be accessible. You can buy them as 100 mm fittings to go on top of stub stacks (shortened SVP’s – Soil Vent Pipes) or as smaller diameters to go on bath and basin waste pipes.
With all the appliances plumbed in, the system can be checked for leaks with an air pressure test. This test should be notified to your Building Control Surveyor as an inspection, vital to commissioning your system as fit for use before you move in.
You need a commissioning certificate for your heating and hot water system, duly completed and signed by the installing and commissioning plumber. This document will need to be included with your home information details.