Planning New Boiler an Rads

[Diggory]

Hi – grateful of some plumbing advice.
My boiler is due a change – its done well but it is old and noisy.
I have always tried to keep system clean [DS40 + inhibitor] but it kettles from time to time so guess there is muck in there moving around. It is a 4 bed house system, circa 20yrs old, 22mm main feed upstairs with micro-bore feeds [behind plaster board] and drop feeds downstairs.

I am thinking that if I change the boiler I want to do it properly and give new boiler a fair chance. So thinking I should change the rads also and wondered what was best order to do things. Should I

Clean old system [ say for a week with DS40] before removing old boiler / old rads.

or

Remove old boiler / old rads without cleaning, fit new boiler / new rads then clean with DS 40. Thinking here was that good amount of muck may stay in old rads / boiler.

Whats the best approach.

Thanks D

 

[gigz]

Better off getting it as clean as possible before fitting the new boiler, you could take all the rads off and flush each leg of pipework with a hose pipe connected, fit the new rads and also a magnaclean or spirovent dirt separator, run it with cleaner in for a week or two, then get new boiler fitted with inhibitor added.

 

[muggles]

If you're going to all the expense of replacing the rads it might be worth getting new pipework too, using a more conventional 15mm to the rads (some people still use 10mm but most are now 15mm). For a start the new rads will almost certainly not be the same width as the old ones, particularly if you're intending to have a properly set up high-efficiency system as the rads may well need to be much bigger than those you have at present, so the current pipework will need altering anyway.

It would of course mean that the new pipework was surface clipped but you can paint it or get it boxed in.

As for cleaning in the event of keeping your old pipework, expect much debate here! I would be inclined to go with a mix of your two options - DS40 and a good flush before removal, then some cleaner in for a week or two once the new boiler and rads are installed. I'd still recommend starting from scratch and getting new pipework too though.

 

[Diggory]

Thanks both for reply.

Sounds like a good clean before removal would be worthwhile.

Bit of a worry about pipework [gulp] - was hoping minimal plaster work.

Thought small boiler would give the efficiency - didnt think would need larger rads.

wonder if I should just turn TV up louder

D

 

[looneyfitter]

Leave the pipework as is.... It will be fine (stop scaring him) We still drop 10mm feeds down to the rads (15mm right above the drop tho tbh)

Better off hiring a power flusher mate. ONly £50 for the weekend from HSS.

Futher more, i hope you not changing the boiler yourself are you?

 

[compheat]

22mm and 10mm to the rads is ok.

don't use DS40 thats for descaling the boiler/ heat exchanger, use the sludge remover either Sentinal or Fernox.

My boiler of choice at the moment is the INTERGAS 36/30 HRE check out there website, Its the easiest boiler i've ever worked on

 

[muggles]

Thought small boiler would give the efficiency - didnt think would need larger rads.

wonder if I should just turn TV up louder

D

No, a smaller boiler most definitely will NOT give you more efficiency (unless the boiler you have currently is far too large). Your boiler should be the correct size for your house. Improved efficiency will come from having a condensing boiler instead of an old-style non-condensing one, having a clean system, having modern controls like Weather Compensation fitted, and running the system at a lower temperature with a higher differential.

The latter is the reason for larger rads - rad heat outputs are generally quoted at around 80ºC/70ºC Flow/Return temperatures, but it's much more efficient with a condensing boiler to run the rads at 60ºC/40ºC (or even 50/30 if you want to get REALLY efficient, but you'd better have a lot of wall space). At 60/40 F/R the rad heat outputs are lower (roughly half) so you need bigger rads to compensate. The general idea is to run them at a lower temperature for longer, with a 20ºC F/R temp differential rather than the traditional 10ºC, so that the boiler stays in condensing mode for longer, making it more efficient.

Hope that's not too much detail!

 

[looneyfitter]

Thought small boiler would give the efficiency - didnt think would need larger rads.

wonder if I should just turn TV up louder

D

No, a smaller boiler most definitely will NOT give you more efficiency (unless the boiler you have currently is far too large). Your boiler should be the correct size for your house. Improved efficiency will come from having a condensing boiler instead of an old-style non-condensing one, having a clean system, having modern controls like Weather Compensation fitted, and running the system at a lower temperature with a higher differential.

The latter is the reason for larger rads - rad heat outputs are generally quoted at around 80ºC/70ºC Flow/Return temperatures, but it's much more efficient with a condensing boiler to run the rads at 60ºC/40ºC (or even 50/30 if you want to get REALLY efficient, but you'd better have a lot of wall space). At 60/40 F/R the rad heat outputs are lower (roughly half) so you need bigger rads to compensate. The general idea is to run them at a lower temperature for longer, with a 20ºC F/R temp differential rather than the traditional 10ºC, so that the boiler stays in condensing mode for longer, making it more efficient.

Hope that's not too much detail!

Wrong there to a point mate. If the rads are si ed right then he would be better under si ing the boiler slightly.. General rule of thumb, undersi e boiler or over si e rads.

More likely to go into condense mode that way.

 

[mickyg]

general rule of thumb. undersize boiler cold house

 

[looneyfitter]

general rule of thumb. undersize boiler cold house

You know what i mean. You wouldnt fit a 30k btu boiler if you needed 6Ok. But a (eg) 50k one would be fine. The house reaches temp and the rads will stay on for longer periods but at lower temp (cos its under rated)

WC works in a similar way

 

[muggles]

I'd always go for correctly sized boiler, at least that can be turned down, one that's undersized can't be turned up.

 

[looneyfitter]

Your not getting my point tho mate. Turning it down isnt going to Give you your temp differential. Slightly undersizing will almost garauntee it.

The rads should be sized right for the house or over.

 

[muggles]

Your not getting my point tho mate. Turning it down isnt going to Give you your temp differential. Slightly undersizing will almost garauntee it.

The rads should be sized right for the house or over.

No, you're right, I'm not getting your point. I'm not sure you're getting mine either, which was that if a house needs a 30kw boiler for example, you buy a 30kw boiler, if this turns out to be too much for effective condensing it can be turned down to, say, 28kw as many modern boilers have this function. If you get a 25kw and it turns out 28kw would be more appropriate you're screwed.

 

[looneyfitter]

No i get your point completely mate. If the house requires 30k you give say 40k rads and 30k boiler. Therfore its undersized and produces a lower return temp as its working harder.

I would generally fit a slightly smaller boiler to an existing system, again there are factors to take in, obviously if its not very well insulated etc then you wouldnt.

The rads should be sized right for the house or over.

you buy a 30kw boiler, if this turns out to be too much for effective condensing it can be turned down to, say, 28kw as many modern boilers have this function. If you get a 25kw and it turns out 28kw would be more appropriate you're screwed.

But if youve done your sums you would know what size to get.

WC works the same way. as said

 

[muggles]

Yeah but that's to do with sizing the boiler using the whole house method and the rads from individual rooms, which everyone does AFAIK