15mm flow/return straight out of boiler

[hi-spec plumbing heating]

most boilers are in houses not a rabbit hutch

 

[JayneKelly]

most boilers are in houses not a rabbit hutch

I`m getting it now i think (sorry) that`s where the heat loss calulation thingy comes in, where can i see one of these please, anyone know?

 

[hi-spec plumbing heating]

type it in google

whos fitting this boiler ?

 

[gas4you]

No, you're still not quite there yet.

You do not add the rad kilowatts on top of the water rating.

24 Kw combi = 9-10 litres hw / min
30 Kw = 12-13 l/min
35 Kw = 15 l/m

All above are approx.

So you see the more powerful the combi, the faster it will deliver the hot water out of the tap, assuming you have enough flow rate entering the combi in the first place.

A 24 or 30Kw combi will usually give you 23/24 Kw to rads max, but will modulate down to around 8-9 Kw, which will be more than adequate for for your rad needs.

Anything over 4Kw approx is usually piped in 22mm then reduced as needed to each rad in 15mm, or until the remaining rad load is less than 4Kw.

All of the above is really what the others have been saying, but you haven't been getting.

Hope I have got through

 

[JayneKelly]

type it in google

whos fitting this boiler ?

it`s already been fitted.

 

[chrishutt]

so rule of thumb is 24kw or more for water then tot up kilowatts for rads and add them on for total boiler size?

No, you don't add the hot water load and heating load together. The Combi boiler does either one or the other, not both together. therefore the boiler is sized for the bigger load, which is always the hot water load.

Why do most plumbers install lengths and lengths of 22mm pipe then in modest houses?

Many houses require 22mm pipework but in some cases it's because plumbers are not aware of how much heat can be carried by 15mm, especially with condensing boilers that have a 20°C temperature drop between flow and return.

 

[JayneKelly]

No, you're still not quite there yet.

You do not add the rad kilowatts on top of the water rating.

24 Kw combi = 9-10 litres hw / min
30 Kw = 12-13 l/min
35 Kw = 15 l/m

All above are approx.

So you see the more powerful the combi, the faster it will deliver the hot water out of the tap, assuming you have enough flow rate entering the combi in the first place.

A 24 or 30Kw combi will usually give you 23/24 Kw to rads max, but will modulate down to around 8-9 Kw, which will be more than adequate for for your rad needs.

Anything over 4Kw approx is usually piped in 22mm then reduced as needed to each rad in 15mm, or until the remaining rad load is less than 4Kw.

All of the above is really what the others have been saying, but you haven't been getting.

Hope I have got through

Brilliant, thanks gas4you.

Thanks, Chrishutt

 

[hi-spec plumbing heating]

type it in google

whos fitting this boiler ?

it`s already been fitted.

if the boilers already fitted the whole question has been pointless

 

[DP]

""Ah haaa, thanks Chris so rule of thumb is 24kw or more for water then tot up kilowatts for rads and add them on for total boiler size?""


Combi boiler power is to deliver HW. Combi will only give you hot water at the tap OR heat radiators (when HW is not called for). HW demand takes priority over heating.

Therefore, when you are not using hot water, boiler will be able to supply radiators totaling 24 kw if boiler is rated at 24 kw. This does not hold true for every boiler.

It may be preferable to have the boiler set to a lower heat output for central heating. It would be akin to using a sledge hammer to crack a nut. Toffee hammer would be better.

 

[JayneKelly]

if the boilers already fitted the whole question has been pointless

Not really as other members like Chris & Dave have had the good manners to educate me, the only pointless part of this post appears to be this contribution from yourself. Don`t answer any questions from myself if they are going to upset you so.

 

[Bahco]

Why do most plumbers install lengths and lengths of 22mm pipe then in modest houses?

So the rads heat up quickly and are able to be balanced easily.

 

[JayneKelly]

Combi boiler power is to deliver HW. Combi will only give you hot water at the tap OR heat radiators (when HW is not called for). HW demand takes priority over heating.

Therefore, when you are not using hot water, boiler will be able to supply radiators totaling 24 kw if boiler is rated at 24 kw. This does not hold true for every boiler.

It may be preferable to have the boiler set to a lower heat output for central heating. It would be akin to using a sledge hammer to crack a nut. Toffee hammer would be better.

Thank you DP & all the boys on here with manners.

 

[bster]

maybe wrong but is it not advisable to pipe the primary flow and returns in 22mm (min) to aid in heat removal from heat exchanger on shut down (when the 'pump overrun' is operating)?

 

[chrishutt]

maybe wrong but is it not advisable to pipe the primary flow and returns in 22mm (min) to aid in heat removal from heat exchanger on shut down (when the 'pump overrun' is operating)?

Good point. Probably depends on whether the ABV is integral to boiler or external. Manufacturer's instructions should be followed on that point.

 

[JayneKelly]

maybe wrong but is it not advisable to pipe the primary flow and returns in 22mm (min) to aid in heat removal from heat exchanger on shut down (when the 'pump overrun' is operating)?

Good point. Probably depends on whether the ABV is integral to boiler or external. Manufacturer's instructions should be followed on that point.

It doesn`t mention anything in manufacturers about having to pipe up flow & return in 22mm, i don`t know if it has pump ovverun, What`s an ABV?