advise on low loss header

[dilalio]

I understand this is an open free forum and I am entitled to share the knowledge and benefit from other people experience. Therefore, i am not asking you to do the search for me. I am directing my question to whoever can positively and politely help.

Sure. In the event that someone has the exact same scenario as you, is a member of this forum, and has read through your post and looked through your data...
The answer is... 42.

 

[muggles]

It's at best a rough guess using the total output of the floor to work out what boiler size you need, unless of course your UFH supplier has carried out a heat loss calculation on your behalf and sized the system accordingly. Not many do that though.

is it safe to calculate the heat loss from the under floor heating CAD design, see attached, if so then, the total output heat from the 3 manifolds is approximately 15kw. add another 1kw for the small radiator in the main family bathroom would make it 16kw.
if the above assumptions are corrected then a system boiler of 20kw would be more than sufficient. Hence, can someone please help with the blow

1. recommendation for a boiler
2. do I still need a low loos header. some of the gas engineer who came around recommended it, some not, few never heard of it.

The CAD design only tells you what output the floor is capable of producing, not the heat loss of your house. Unless you've provided the UFH supplier with information such as is requested by the Heat Engineer software, it's very unlikely that they've done any kind of calculation to determine whether their system is actually suitable for your home or not. That being said, 15kW is at the top end of where my back-of-an-envelope guess got me to so it's probably not a million miles away. I'd still recommend a full heat loss calculation to confirm, but some good options would be...

Viessmann 200-W 19kW
Worcester 4000 15kW
Ideal Vogue Max 15kW
Intergas Xclusive 24 (which is actually 18kW to heating)

You don't need a low loss header but some form of hydraulic separation at the manifolds may be beneficial. You should look to have a hot water priority system installed (the Viessmann, WB, and Intergas can all do this, not sure about the Ideal).