Is 22mm boiler output enough?!

[cog-n-chips]

Hi, I have recently fitted central heating to a large house, the system runs 14 radiators and the total BTU requirement is ~59k.

I have chosen a Worcester Bosch 32 CDi Compact for my boiler. The boiler heat output seems to be ample for my system and hot water needs.

My only question is, if 22mm copper pipe can only comfortably supply about 45k BTUs, and the boiler has a 22mm output, how will this be enough to support my whole system??

The pipes from where the boiler is going are a 22mm feed for the top two floors, needing about 29k BTU, and another 22mm feed for downstairs, about 21k BTU. Will the 22mm boiler output not supply my system to full heat? I assumed a 28mm boiler output would cover this, but am hard pressed to find any reasonable sized units that have this.

Any advice is much appreciated, James

 

[Sparkgap]

59k works out about 0.2 l/s flow rate, a bit high for 22mm but would depend on length of pipe taking the full amount and size of pump. Personally I'd increase to 28mm off the boiler until the tee to upstairs. Lower velocity means less noise.

 

[doitmyself]

So you have approx 17-18kW of rads, and have chosen a boiler which produces 24kW for heating and 32kW for HW.

1. Have you calculated the heat loss from your house (rad sizes are not always a good guide)?

2. Have you measured the incoming cold water flow rate to check that you need 32kW? (You need 2.5kW per litre/min.)

 

[Unregistered]

How could I increase the boiler output to 28mm though? If the output is 22mm standard then surely it would need adapting up to 28mm and the problem would still be there. The system is quite large, probably about 150m of piping in total. I don't know a GSR is, but the original quoting plumber recommended a 28k to 34k boiler. I have since added 2 more rads. Figured 32kw would be nicely in the middle.

 

[hammers4spanner]

Bit confused you say you originally had a new central heating system but you have just added two more rads to your new system ???

How come you never done this in first instance?

Don't sound right to me

 

[gpbeck]

A small restriction to 22mm at the boiler outlet is not as significant as a long run of 22mm

 

[gmartine]

DIY job.

 

[doitmyself]

59k works out about 0.2 l/s flow rate, a bit high for 22mm but would depend on length of pipe taking the full amount and size of pump. Personally I'd increase to 28mm off the boiler until the tee to upstairs. Lower velocity means less noise.[/QUOTE)
0.2 l/s gives a velocity of approx 0.6 metres/sec in a 22mm pipe. Normally flow noise doesn't occur until the velocity is over 1.5 m/sec. 28m pipe would give a velocity of approx 0.4 m/sec, which is getting close to the minimum recommended 0.3 m/sec.

 

[Scott_D]

Post some pictures of the boiler and pipework below so we can see what's what

 

[Unregistered]

I haven't bought my boiler yet, I am just making sure it is up to the job first.

The pipe from the boiler output to the T-piece for upstairs is only about 15", but I think I will up it to 28mm for that length, it would give peace of mind.

Also @ mr qualifications... "Don't sound right to me" doesn't sound right to me.

 

[hammers4spanner]

But it don't sound reet

 

[ShaunCorbs]

Will be enough and don't forget you need to be gas safe to put the boiler on the wall / open the box

 

[Unregistered]

Oh so you actually need a gas cert plumber to fit the boiler to the wall? Blimey, that's good information. I will order the boiler and find one to fit it, thanks.

 

[PlumbBobBob]

don't forget any guarantee on the boiler you will have to sort out. the Gas engineer won't want to guarantee it any problems and they will charge for call backs. the best way is for the engineer to supply the boiler.

 

[lame plumber]

why not employ a qualified technician to look at what you have done, do the requisite calculations for heat loss and boiler sizing and take it from there. Best to get it right before having to pay for expensive repiping is needed.

 

[Dotty]

OP's attitude has made me decide to close this thread.