Condensing combi - acidic waste?


Postby VicSten » Sun Mar 09, 2008 7:08 pm

I'm getting new heating system - new radiators (are those old fashioned 3 column ones any good?), shower in the bath and new boiler in a two bedroom flat and, usually, just me living in it. I've been led to believe a combi condensing boiler will be the best and I can get rid of the rubbishly inefficient large water tank (it has a think metal lid and bad electric emersion) to give me more storage space.

In getting quotes, I had one chap tell me I couldn't have a condensing boiler as the residue water waste is acidic and will burn through all the metal pipes - not just in my property (I thought that wouldn't be tto difficult/expensive a job to change them to plastic) but the waste pipes outside which all flats drain into are metal. In retrospect, I think this is rubbish as there must be a lot of acidic waste and other crap people put down their pipes, and there won't be a lot of acidic waste from my boiler so it would be very dilute with all the other waste water...or am I wrong? Is it that acidic and destructive? Neither of the other chaps quoting mentioned it.

Who's right?

And, which boiler should I go for? I don't mind spending money to get the best one that will last the longest and be the least bother. Should I instead go for a combi or not - should I go for a standard boiler, condensed or not, with a pressurised tank?

The more I look into it the more confused I get!
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Postby DONFRAMAC » Mon Mar 10, 2008 2:46 am

The condensate liquor is indeed acidic, and has to be plumbed out to a soakaway, at least 0.5 metres away from the building. Mine uses 1" bore white PVC waste piping, leading into a larger size, before going underground to a gravel-filled perforated PVC pot below my path. The 2 sizes of pipe are not sealed, and allow air-venting.
The closer the boiler is to your hot water outlets, the quicker the arrival of the hot water. The radiators don't operate when using DHW.
I now have a large cupboard to convert into an electrically heated airing cupboard, and no stock of stored hot water:-- but the thermostatic blender shower is just great!!
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Postby htg engineer » Tue Mar 11, 2008 9:26 am

The law in England & Wales changed in April 2005, which means only a condensing boiler can be fitted as a replacement boiler or complete new installation. There is a minor loophole to this law where, in exceptional circumstances, the local authority, can agree to an exemption certificate allowing a non-condensing boiler can be fitted.

By law it should be a condensing boiler, you wont get anyone to fit a non-condensing boiler legally unless you apply for exemption - If a condensing boiler can be fitted - then it must be.

The question on discharging the condensate into metal waste pipes has been brought up many times. Manufacturers state that if the pipes are used for sinks, bath, shower etc etc - the water from these would be enough to get rid of the condensate before it could cause any damage to the pipework.

You can get condensate acidic neutraliser, it's similar to fitting a scale reducer to a water pipe. Or as DONFRAMAC says, install a soakaway.
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Postby VicSten » Tue Mar 11, 2008 8:41 pm

Fantastic - thank you for the advice. I thought it was odd that nobody had mentioned it before and I thought that other waste would dilute it. Many, many thanks!
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