Metric to english fitting conversion

Arthur Fellows

I am looking at buying a european combi-boiler to install in my home. I would like to install wall mount radiators with a two pipe system (PEX) for heating and also supply the domestic hot water for my home. I have a mechanical engineer who is going to help me size and specify the system, however, one seemingly simple issue is troubling me. The fittings on the boiler are 22mm (heating in/out)15mm (domestic hot water in/out)and 22mm (gas in, Black Iron Pipe). There is also a 15mm pressure release valve. I suspect that I can use PEX connections for the heating loop and pressure release, I may even be able to convert my copper water supply lines to pex for the connections to the boiler, but does anyone have a solution for converting my 3/4" black iron pipe LP supply line to 22mm for connection to the boiler?

J.C.A._3

Arthur,

If you're purchasing this boiler in the states, the bushings/couplings SHOULD be in the trim kit. I know with Buderus and Viessman, all the connections come with them to shift from straight cut thread to "standard" tapered threads.(Why that term is used , I have no idea,in the rest of the world, METRIC IS standard!). Chris

Aidan (UK)

In the past,

I’ve obtained adaptors for US/metric pipes or NPT/BSP threads from Swage-lok, a US company with UK outlets. Not cheap (over here), but high quality. You’ll probably find similar adaptors can be supplied by most large pipe fitting suppliers.

However, I’m very surprised that you’re considering an European combination boiler. They are marketed for small European apartments and the design intention is to squeeze all the heating system components into a small wall-mounted package and to minimise the installation costs. There are disadvantages. I am frequently asked about them and almost invariably tell people to avoid them. Many people are disappointed with their hot water delivery.

If you take the front off some of these boilers, you open a can of worms with a quart of worms in a one pint can. This is OK if the technician has attended the factory training courses, but your local man might not know what he’s looking at.

The waterways in the brazed plate heat exchangers (generating the domestic hot water) are narrow and can easily be obstructed by limescale. The problems with limescale are most severe in areas with hard water. If you have problems with limescale, then your combi heat exchanger will scale up. You should enquire about the costs involved in chemically descaling the secondary side of the heat exchanger.

The hot water flow rate is generally lower than you’ll get from a conventional indirect storage hot water system. The relevant British Standard BS 6700 recommends a flow rate of 0.3 l/s from a ¾” bath tap. This would represent a heat flow rate of about 60 kW if the water is heated through 50 degC. Since most Euro domestic boilers are under 20 kW, this isn’t going to happen. Whilst there is a hot water demand most combi boilers will stop the flow to the heating system.

Combi boilers are most applicable in well-insulated apartments, where there’s no loft space & no room for an indirect water heater. Generally, I wouldn’t put one in a house.

I have got one in my house, but I’ve also got a water softener and the combi only supplies hot water to the shower, at mains pressure. I’ve still got an indirect hot water storage cylinder, which supplies the rest of the house from a cold water storage tank in the loft.

See the articles at;
http://money.guardian.co.uk/print/0,3858,4748267-109001,00.html

and

http://www.diyfaq.org.uk/plumbing/combi.html

I hope you know what you’re getting into. When in Rome, do as the Romans. If you’re not in Rome, get a Munchkin like everyone else.

PS. Pipe the outlet from the pressure relief/safety valve in copper. If it should ever be used in anger, it may be discharging steam.