boiler sizeing

[Dan Robinson]

They should work a treat with your nice soft Welsh water.

You know where to go for top line tech support on these though .

 

[Alfie25]

A boiler will only condense if the system has been designed so the return temperature is low enough (<55C) for condensing to occur. If a condensing boiler has replaced a standard boiler, there is a good chance that it will only condense on rare occasions because the system was originally designed for a return temp of about 65C.

Could you explain this a bit more to a lay person like myself please. I'd like to understand it as I'm looking to have my system boiler replaced with a combi. The system boiler I have at the min is a modern 12kW condensing boiler, that replaced the original one (whatever make that was) but the rest of the system (pump, pipes, tanks etc) are the original system. Mine condenses plenty!

 

[Steelmasons]

Nothing to do with working flat out.

A boiler will only condense if the system has been designed so the return temperature is low enough (<55C) for condensing to occur. If a condensing boiler has replaced a standard boiler, there is a good chance that it will only condense on rare occasions because the system was originally designed for a return temp of about 65C.

Flue gas dew point temp will be dependant on CO2%.

 

[onlyfitidealboilers]

Ideal, don't 24kw combis have 19kw max heating output 24kw for dhw? the heating output is never as much as dhw. Then after the boiler figures out the output required from it it will modulate down to suit the load. So combis aren't oversized, but you need a minnimum (24kw) output on the hot water side to be able to provide acceptable hw rates. On most boilers you can set the load for the heating yourself...

That Chantelle doesn't seems very helpful, just likes to mouth off it seems.

Always remember, it takes more energy to put the heat into the water from cold. You want to heat it and keep it hot so a boiler chucking out 30kw say when all you need is 12kw will cycle which is inefficient. That's about my limit, need to learn more. Any answers to this will be appreciated, I promise not to tell you to get over yourselves or that your wrong

No they do not. All combi boilers will modulate for sure, however the flow & return pipe work should be no less than 28mm off boiler due to it's being able to pump out 24kw down the flow. Other wise it will short cycle on off on a under sized system. Remember no more than 17.6kw down a a 22mm pipe, carnt argue with physics

 

[Dan Robinson]

Even at 50/30?

 

[srhawksy]

Why 28? you get the 24kw down the 22, not that you'll use all that while on heating so why go to the extra cost? If it is the case we should be fitting 28mm so far in the system shouldn't the connections from the boiler be in 28mm? what if you fit a boiler, and then change the load required to suit the house (partial load) vaillant let you do that as you go through the commissioning programme, does the vouge? (only fitted one vouge) it will never chuck out more than you've asked it eg. 12kw??

Am I being thick now?

 

[srhawksy]

Where do you learn all the really in depth stuff, Dan you said you went to uni sometime in the distant path.... What did you study?

I don't remember pipe sizing in college.....

 

[Dan Robinson]

I read English Literature with a bit of computer programming and Anglo Saxon linguistics thrown in.

Reading and listening to the right people basically. That's why I hoover every bit of technical literature I can for the ccr

 

[D_Hailsham]

Remember no more than 17.6kw down a a 22mm pipe, can't argue with physics

But your physics is assuming a differential of 11C at the boiler. If you are using a boiler designed for a 20C differential, the flow rate is approximately half; so the same 22mm pipe can now carry 32kW.

 

[D_Hailsham]

Mine condenses plenty!

What is your evidence?

 

[Alfie25]

Mine condenses plenty!

What is your evidence?

The condensate pipe runs outside and into a surface water drain. When the boiler is on it emits a steady (almost non stop) drip. Admittedly I haven't sat and watched it for hours, but when the boiler is working hard (all radiators calling for heat, sometimes with HW being called at same time) then condensate is coming out the condensate pipe.

 

[D_Hailsham]

The condensate pipe runs outside and into a surface water drain. When the boiler is on it emits a steady (almost non stop) drip. Admittedly I haven't sat and watched it for hours, but when the boiler is working hard (all radiators calling for heat, sometimes with HW being called at same time) then condensate is coming out the condensate pipe.

If you are getting a steady drip then only a minimal amount of condensing is taking place; the return temp will be about 55C. The amount of condensate (water) produced increases as the return temperature reduces. So a boiler running at 50/30 will produce more condensate and a higher output (kW) than one running at 75/55.

 

[Alfie25]

OK, so going back to the bit I quoted you saying earlier, are you saying the pipework needs fully overhauling when fitting a combi to a system that was originally designed for an open vent? Otherwise the return will be too hot and it won't condense?

 

[Dan Robinson]

No. But if changing any rads at the same time go as big as you can.

 

[srhawksy]

I read English Literature with a bit of computer programming and Anglo Saxon linguistics thrown in.

Reading and listening to the right people basically. That's why I hoover every bit of technical literature I can for the ccr

What is this ccr? and where does one find it?