Combi boiler - would I use more water? Advice please.

HappyMJ

phill99 wrote: »

This is a ridiculous discussion. The price of a cubic metre of water is probably less than 1% of the cost of a cubic metre of gas.

So you would be happy to waste more gas rather than waste water? Semms a very bizarre approach to household budgetting.

Are you sure about that? 1 cubic metre of water South Staffs Water is £1.81. 1 cubic metre of Gas is about 11.15kWh and at Ebico's high price of 4.788p/kWh makes it £0.53 per cubic metre. Gas is cheaper than water.

Maybe I could look at it from a different angle.

The shower runs at 12 litres per minute that's 720 litres per hour costing £1.30 per hour in water. The boiler uses 2 cubic metres per hour of gas costing £1.06 per hour in Gas (at Ebico's high standard price). I'd rather waste the gas rather than the water.

My showers are about 3 to 6 minutes each so cost £0.12 to £0.24 each approximately.

ziggyman99

You could fit one of these clever little devices.....

http://www.combisave.com/

martinthebandit

paulsad wrote: »

Not everyone knows everything though....

Very true, the only daft questions are the ones you don't ask, and some posters seem to go out of their way to make some people wary about asking them.

squeekswhenwalking

As a heating engineer, I would personally preferr to fit a new condensing heat only boiler and a highly insulated cylinder, you then have the option for other heat sources in the future, plus if you have llong pipe runs a dhw pump could be fitted to ensure hot water is immediate

martinthebandit

Saver0811 wrote: »

I think these days you have to get a combi boiler, but be warned,

If the drain pipe has a run outside, it will freeze in the winter, and the boiler will stop working.

So NO CH just when you need it the most.

Well known design fault.

Backup with electric space heater if this is so.

Unless of course it is fitted correctly and then it wont.

No problems with ours even though the condensate pipe does run outside.

ziggyman99

Saver0811 wrote: »

I think these days you have to get a combi boiler, but be warned,

If the drain pipe has a run outside, it will freeze in the winter, and the boiler will stop working.

So NO CH just when you need it the most.

Well known design fault.

Backup with electric space heater if this is so.

I presume when you talk about drain pipe you mean the condensate waste.

Rubbish and scaremongering. I've NEVER had a condensate pipe freeze on a boiler that i've installed. Properly done, as per regulations and manufacturers instructions, and itis VERY UNLIKELY freeze.

It is not a design fault but an error during installation that allows it to freeze.

Also, it is not just combi boilers that produce condensate. Heat only and system boilers do aswell.

ziggyman99

Saver0811 wrote: »

Thank you for reminding me of the correct term.

Google begs to differ

http://www.google.co.uk/search?hl=en&source=hp&biw=1434&bih=654&q=condensate+pipe+freeze+combi+boiler&oq=condensate+pipe+freeze+combi+boiler&aq=f&aqi=&aql=&gs_sm=e&gs_upl=3188l17865l0l19221l39l35l2l16l16l0l220l2546l3.11.3l17l0

Google is wrong then. You stated it WILL freeze. That statement is incorrect. I've been to lots of boilers with frozen condensate pipes but I've never seen one that has been done correctly freeze. I see many condensate wastes done incorrectly so there are going to be lots of people moaning on various forums, hence the Google results.

ziggyman99

Saver0811 wrote: »

British Gas installed, with external large bore pipe run of approx 6 feet, but fed with a small bore pipe for 3 inches.

In response to your amended post.

There you are. I presume you are saying they have fitted your condensate with 3 inches of 21.5mm overflow pipe externally before going into a 32/40mm waste pipe? That is a bad installation, hence the freezing. Don't worry your not the first or last person to have a bodged install by BG.

C_Mababejive

I do think that a lot of combis are mis sold and fitted in the wrong properties where they are unsuitable.

I also think that they can be incredibly wasteful of both gas and water despite the received wisdom that they are more efficient.

But what do they mean by more efficient?

Well when talking about modern forced draught condensing boilers,what we mean generally is that the combustion process is more efficient in that more heat value is extracted from the gas before its products are exhausted out the flue.

Fine ...

But to the layman..the term efficient means cheaper to run,better,faster ,,whatever..

In simple terms,, when a combi is fitted,the hot water storage vessel gets binned. It is actually possible to retain it but its rarely done.

So..when you turn your tap on...the boiler senses this, it stops supplying the heating circuit and revs up to FULL output which will be in excess of 30 Kw. The reason it does this is that it takes cold water from the cold main,slows it down and supplies lots of heat to get it hot enough to send directly to the cold taps.

This takes time....so you end up running off a certain volume of water which is gradually warming up ,until it gets hot enough. But the boiler is still running at over 30 Kw or 102,000 Btu/hr in old money.

In effect,you are wasting that energy and exporting it down the drain...

So you wash your hands,rinse a cup..turn the tap off until next time..when the whole process repeats.

Many combis use mechanisms to provide faster response. They will have either a pre heat system or will have a small amount of stored hot water on board or both.

So what happens is that even when your not drawing hot water,the boiler fires periodically to preheat itself so that it will respond quicker when you do decide to turn the tap on. It also fires periodically to top up the preheated stored volume of hot water..

So even when your not using hot water..you burn gas..

I am a great fan of stored hot water systems...

I think in future decades,we will be ripping combis out and refitting high efficiency storage systems.

Many combi's especially the older.more asthmatic ones,can only feed one tap at a time..imagine that. Its the 21st century and we can only run one hot tap at a time and they call that efficiency and progress...ROTFL.

So getting back to storage... i think the future is optimal volume pressurised hot water storage fed by a HE system boiler. Best of both worlds.

My system her is a little old but it works just perfectly.

I have a gas wall boiler thats maybe 25 years old. Its max output has been range rated down to 38,000 Btu/hr.

Its fully pumped and i have a combination cylinder in the cupboard.

I can have lots of hot water and run as many taps as i like and the reheat time isnt that long.

Any heat radiated from the cylinder isnt lost as it warms the airing cupboard/house unlike your combi,where lost heat goes down the plug hole.

My boiler input 38,000Btu/hr

Combi heat input ..at least 102,000 Btu/hr

In simple terms..thats all you need to know..

martinthebandit

C_Mababejive wrote: »

I do think that a lot of combis are mis sold and fitted in the wrong properties where they are unsuitable!.........

My boiler input 38,000Btu/hr

Combi heat input ..at least 102,000 Btu/hr

In simple terms..thats all you need to know..

Absolute nonsense.

I live in a 3 bed, 2 bath detached bungalow and I have a combi boiler for water heating.

My combined gas and electric bill is currenty £40 a month, whats yours?

I suspect THATS all we need to know