Rad Sizing - Condensing Combi - Help

[machineage]

I wonder if someone could advise best practice regarding rad sizing...

House is Victorian semi - 5 beds - 3 reception - 1 bath - 10ft ceilings. Longest run to rads is 25 metres for the upstairs front bedroom - the boiler is at the rear of the house.

I have just finished calculating the heat loss for each room using Stelrad Stars - the total of which is in the order or 20kw. This was calculated at a minus 5°C outside temperature - this recalculates to around 18Kw at minus 3°C.

The heat loss figures as yet do not include a 10% pipe loss / fast warm up calculation - or a BOE calculation. I'm not sure whether the quoted outputs from Stelrad are for BOE or TBOE etc. Will check with them. I wonder too what flow rate the outputs are based upon and how much that matters?

Boiler is an Intergas 36/30 - radiators will be Stelrad Softline. Boiler will have an external compensating sensor.

The boiler manufacturers data recommends a 20°C supply / return differential if possible - but don't state an ideal return temp. I'm going to assume / aim somewhere below 55°C to achieve better condensing.

So - what should be my next steps?

I can calculate each individual room Delta T as I have the correction table for the rads - which will enable me to more accurately size them.

What flow / return temps should I use? 70/50 - 73/53 - 75/55 - any other combination? I see many installers struggle to get a 20°C differential - what factors affect this? Should i aim for a 15°C differential or less?

What other matters should I take into account?

Thanks!

[SimonJohns]

Wow. I think you've really put too much effort in to this. But very good for what you have done

If your worried about flow rates

Never run more than 2 rads off a price of 15. And run 22 as far as you can

I think youll be more than fine

[SimonG]

Wow. I think you've really put too much effort in to this. But very good for what you have done

If your worried about flow rates

Never run more than 2 rads off a price of 15. And run 22 as far as you can

I think youll be more than fine

Don't think I put that much effort in when I was an apprentice at college!!!!

[leelister6]

Just cube yer room in feet, times by 4, that will give ya BTU's then go 2 rad sizes up. Then go 4 a pint, watch Top Gear, gi your lass a slap an fall asleep on settee wi your kecks round your ankles. That'lle be £200 for the advice. I accept paypal

[machineage]

I thought this was a forum full of pro's

I like to do things to best practice - learned the hard way!