15mm heating circuit

[namsag]

It can work right if he just connected the boiler flow and returns into a passing heating circuit, This is a normal boiler so flow and return would need to be run back to where the orginal boiler flow and return joined the heating and H water circuit .

 

[Agile]

This is a 24 kW boiler supplying a heating load of perhaps up to 12 kW and a hot water load of also perhaps about 12 kW.

The usual allowance for hot water is to add another 2-3kW to the heating load, not 12kW. The water will heat up very quickly.

You are sounding more and more like BigBurner who only reads brochures and has no practical experience of heating systems and does not understand the underlying principles.

The allowance for water heating when doing a boiler sizing calculation is indeed just 2 kW.

However, that does not mean that you only supply the cylinder with 2 kW ! If you did that it would take two hours to reheat!

Modern cylinders can absorb 24 kW when cold and need high power to reheat quickly.

The 12 kW that I suggested was the situation prevailing when the heating is on as well and the boiler output is split between heating and water.

And yes, the boiler is oversized! A 15 kW would have been adequate. But even a 15 kW would have needed the 22 mm pipes as the whole output would be needed at either the cylinder or heating.

Now he has a more powerful boiler fitted then outside the heating season the water can reheat with the full boiler output of 24 kW and even during the heating season the water can still reheat quickly.

Tony

 

[DanDare]

Thanks Agile and D_Hailsham for all your responses.

A few questions I can answer:

The CH flow is indeed 22mm upto and about 2 metres beyond the motorised valve. 15mm from there. The HW flow and combined return is 22mm

Regarding the kitchen rad, we used to have 2 radiators in the room (old fashioned single panel type). We wanted to remove one, and upgrade the other to compensate. The two rads seemed to heat the room ok - but last winter was mild and we had the work done in the summer!

According to my very rough calcs (room is about 4m x 6m, 6m outside wall solid brick, with wooden window and 2.4m square french doors, both 4-6-4 double glazed) - we need around 6000-7000 btu/hr - so our 1400x600 single convector is insufficient. The question is, if I replace it with a similar size double rad, will the pipework limit any increse in heat output.

Thanks again for everyone's help and advice![/quote]

 

[D_Hailsham]

You are sounding more and more like BigBurner who only reads brochures and has no practical experience of heating systems and does not understand the underlying principles.

I can assure you that I am not BigBurner, though why you should think he has no practical experience baffles me.

The allowance for water heating when doing a boiler sizing calculation is indeed just 2 kW.

However, that does not mean that you only supply the cylinder with 2 kW ! If you did that it would take two hours to reheat!

Modern cylinders can absorb 24 kW when cold and need high power to reheat quickly.

The 12 kW that I suggested was the situation prevailing when the heating is on as well and the boiler output is split between heating and water.

I think you are misinterpreting what I wrote. I was not suggesting that the cylinder could only absorb 2kW, so that was the maximum which could be added to the heating kW to give the boiler size, but that there was so much heat available for Hot Water, even when the CH was on, that the water would heat up very quickly. I don't know where the 2KW figure comes from.

And yes, the boiler is oversized! A 15 kW would have been adequate.

Not disputing that

But even a 15 kW would have needed the 22 mm pipes as the whole output would be needed at either the cylinder or heating.

Agreed

 

[D_Hailsham]

According to my very rough calcs (room is about 4m x 6m, 6m outside wall solid brick, with wooden window and 2.4m square french doors, both 4-6-4 double glazed) - we need around 6000-7000 btu/hr - so our 1400x600 single convector is insufficient.

That's about 2kW, so 15mm for the pipe from the previous rad to the kitchen rad is OK. When you change to 22mm depends on what other rads are on the same branch.

Starting at the kitchen rad, add up the kW for each rad on the same branch. When the total reaches exceeds about 7kW it's time to think of 22mm pipe. There is no hard and fast rule when you change over - it depends on several factors. See the Copper in Small Bore Heating document I referred to earlier.

 

[DanDare]

Hi D_Hailsham

I'll do those calcs and see.

- and thanks for all your constructive input - really helpful!

 

[Norcon]

Agile wrote

Presumably he was not CORGI registered

Dandare wrote

and yes, was corgi registered

Classic.
Why do you always assume anyone not corgi registered are the bodgers Agile? Its clear many rgi's should stay well clear off heating system installation.

 

[DanDare]

Hi D_Hailsham.

Using Stelrad figures - and interpolating a bit for old non convecting rads, and rounding up here and there:


Ground floor has:
1400x600 single (soon to be double):1372W (soon 2425W)
1600x600 single non conv: 1000W
2800x600 single non conv: 2500W
TOTAL GROUND FLOOR: 4.9kW soon to be 6kW

1st Floor has:
1750x600 single non conv: about 1200W
950x600 single non conv: about 600W
1000x600 double conv: 2kW
Towel rail: say about 700W max?
TOTAL FIRST FLOOR: 4.5kW

Attic conversion has:
1400x400 double conv: 2kW
Towel rail: Say 700W?
TOTAL 2.7kW

House Total: 12kW ish , soon to be 13.2kW

So using your 7kW maximum, the ground floor should be fine on one 15mm circuit, and the other 2 floors on another, with 22mm distribution supplying them from the boiler.

Does that sound right?

If I do run 22mm pipes as per your drawing, do I simply refill and rebalance, or is there technical stuff, adjusting bypass/pump/boiler settings?

Final thought: with the current 15mm circuit, am I simply not getting good performance from the rads and the system as a whole, or am I at risk of knackering the pump/boiler?

Thanks so much for the advice!

 

[D_Hailsham]

TOTAL GROUND FLOOR: 4.9kW soon to be 6kW

TOTAL FIRST FLOOR: 4.5kW

TOTAL ATTIC 2.7kW

So using your 7kW maximum, the ground floor should be fine on one 15mm circuit, and the other 2 floors on another, with 22mm distribution supplying them from the boiler.

On those figures the piping shown in my "after" diagram is OK. You only need 22mm down to the first floor; the drop from first to ground can be in 15mm (which you have already). But, as Agile says, the pipework from boiler to pump, mid-pos, hw cylinder and down to the fist floor must be in 22mm. As shown in this diagram.

Untitled

• D_Hailsham
• 7 Jan 2009
• 1

If I do run 22mm pipes as per your drawing, do I simply refill and rebalance, or is there technical stuff, adjusting bypass/pump/boiler settings?

Balancing should be all that is necessary, which includes the adjustments you mention. See Balancing Procedure

Final thought: with the current 15mm circuit, am I simply not getting good performance from the rads and the system as a whole, or am I at risk of knackering the pump/boiler?

Just poor performance.

 

[DanDare]

D_Hailsham

Thanks again so much - for all the advice, and for taking the time to draw the diagrams etc!

 

[D_Hailsham]

No probs - it what this site is for; DIYers helping other DIyers (often with useful input from the pros. )