Combi boiler / low loss header / UFH advice

[DannyH]

Hi,
hoping someone can help on this.

I'm currently renovating a small cottage, and putting in a new heating / hot water system with 3 radiators and an 80m loop of UFH, a shower, bath, sink, handbasin, dishwasher and washing machine, using a 25kW Worcester Bosch greenstar Si combi boiler. All fairly standard, though the UFH seems to complicate things more than I'd expected.

THe UFH has a thermostatic mixing valve with flow and return from the main heating system, and it's own pump, so there will be two pumps in the system - the boiler pump and the UFH pump. I was planning to to do most pipework myself to keep costs down, and the plumber doing the boiler install advises a low loss header to seperate the two pumps. I only sort of understand low loss headers, and certainly not to the extent of sizing one.

Any comments on the design, or links to more information on low loss header design would be much appeciated.

Cheers
Danny

 

[DeltaT2]

Not sure why you'd need a LLH for a wee system like that?? A bit overkill I'd say!!

Nothing complex about the UFH, are you sure your 'Plumber' knows what he's doing?? There's a lot of cowboy course chancers about, have you got one of these?

 

[DannyH]

Thanks for the reply. I thought overkill too, hence the post on here. However, this is someone I trust and usually I think he knows what he's talking about. I'm a builder rather than a plumber, but I've worked on other projects with him, and plenty of people I know think he's good.

His reason was that the two pumps don't work too well together; as far as I understood him the UFH pump could be forcing water through the boiler at the wrong rate. Any comments?

cheers
D

 

[DeltaT2]

The UFH circulation pump is fitted to circulate water through the floor loop, as you can imagine; the floor loop pipes have a high resistance, hence the need for the UFH pump, given that you have such a small UFH loop then that may be his reasons for a LLH, but there's certainly way round fitting a LLH on a small system.

 

[D_Hailsham]

I was planning to to do most pipework myself to keep costs down, and the plumber doing the boiler install advises a low loss header to separate the two pumps. I only sort of understand low loss headers, and certainly not to the extent of sizing one.

If the plumber doing the install recommends a low loss header, then he should be sizing it and providing you with a diagram showing how it connects to the boiler, rad system and U/F system.

 

[picasso]

You might want to change your plumber for one that knows how to install an s plan on a combi, putting a llh is not too clever.

 

[kevplumb]

You might want to change your plumber for one that knows how to install an s plan on a combi, putting a llh is not too clever.

sizing and making one is tho

 

[Dan Robinson]

Would be better off spending the LLH money on going up to a CDi boiler and weather compensation.

Fitting a LLH to this kind of system sounds crazy to me.

 

[Agile]

I can kind of guess what the plumber is worried about.

However, if an auto bypass valve is fitted to the boiler then that will overcome his fears that there will be insufficient flow rate through the boiler.

If a LLH was to be used then as the boiler has an internal pump then a third pump would be needed to create flow in the heating load ( radiators and UFH ).

Tony

 

[D_Hailsham]

If a LLH was to be used then as the boiler has an internal pump then a third pump would be needed to create flow in the heating load ( radiators and UFH ).

I had thought about needing three pumps and then realized that the plumber may have been thinking of making the three rads part of the primary, with the LLH at the end of the chain. You would then need only two pumps.

How about using closely-spaced tees instead of a LLH to feed the U/F?

 

[DeltaT2]

Eh???!! He only needs 1 additional circulation pump for the UFH manifold or mixing valve, two zone valves and a by-pass valve. LLH??!! C'mon!!