Extending pipework - Central Heating System

[desktop987456]

I have a 320 sqft double storey house with 6 bedrooms. The house is serviced by two heat only boilers (non condensing); a 120k btu (35kw) and a 70k btu (20kw). Both Boilers are installed at ground floor (120k at front and 70k at the back). Front boiler serving front downstairs and upstairs rooms and the back one serving ground floor and upstairs rooms at the back. 22mm Copper pipework from boiler with branches going upstairs and terminated to radiators 8mm. The house has larger rooms at the front side and smaller rooms at the back.

I must tell you that this was installed without heat loss calculation so the front boiler is only serving;

Ground Floor= a 252 sqft room; 320 sqft. Lounge with 600x1400mm Type 11 radiators installed in each room. Both rooms maintain temperature very well.

Upper floor 252sq.ft room (Type 22 radiator recently installed) and a 650sqft lounge with fan assisted coil unit installed.

What I am trying to achieve

I am on my learning curve with the system and my heat calculation tells me that the front 35kw boiler would be enough with 12 radiators in total for the whole house including small radiators in bathrooms. To do this I need to extend the pipework from front to back; two copper pipes 22mm for 35ft length.

Questions :

1. From where do I take a connection out from existing 22mm copper pipes; upstairs or downstairs? Would this length require a separate pump to be installed to serve pipework this long?

2. Would the existing heating be compromised (front rooms if I extend the pipework)?

3. Would I be saving any money; running two boilers instead of one. I have gas rated the boiler and bigger boiler consumes 1m3/hr at 70deg C flow. Extending the pipework will increase my gas usage, correct?

Many Thanks in advance.

 

[desktop987456]

My existing pipework is copper, should i go for PEX or copper?

 

[oldbutnotdead]

You may hit capacity limits on the 22mm 'main' - trying to stuff 35kw down one 22mm tube is optimistic to say the least. If you were designing it from scratch you could look at 28mm risers out of the boiler and 22mm branches on each floor/group of radiators
3 1 large boiler running near full load should be more efficient than 2 boilers running at lower capacity. If the boilers are both modern then there won't be a massive saving, if the 35kw is old and less efficient than the 20kw your running costs may increase for the same heat output.
4 Up to you. Bear in mind the internal bore (and thus thermal capacity) of placcie is significantly less than that of copper. Also remember that placcie fittings are bulky, ugly and expensive- placcie works best as a manifold system rather than the traditional trunk and branch setup seen in copper.

 

[desktop987456]

Thanks. Both are old boilers hence I am looking at running one large one instead of two but I am also weary about the gas usage hence this post.
I dont know anything about plastic pipes but was quoted by a plumber so I thought I'll ask someone more knowledgable, since my existing pipework is of copper so it makes more sense to go for copper but I was led to beleive that elbows and bends on copper pipes restricts the flow or pressure of water to radiators?

 

[oldbutnotdead]

Elbows and bends in any piping system resist the flow of water through it. The reduced bore of plastic restricts flow compared to the same outer diameter copper.
Plastic is quicker and easier to install than copper, that's probably his main motivation

 

[desktop987456]

Thank you. I'll be going for copper 22mm then. The plumber has given me two options for extending the 22mm pipework (50ft each for flow and return);
Option 1 : Run two pipes from ground floor along the skirting (50ft length) to connect with back piping (making smaller boiler redundant)
Option 2 : install circulation pump on extending piping to maintain the flow to back radiators.

 

[oldbutnotdead]

Again without a lot more detail it's hard to assess your scheme. It sounds like rather a large house, just adding a pump may not solve anything. This 'plumber', is he the only one quoting? Is he planning on insulating the link 22mm tubes?
Is there any zoning or other control gear on the system? (At the moment, you can heat the extension completely independently of the rest of the house- different times, different temperatures. Without some zone valves or smart radiator valves you will lose that control, heating the whole house will always cost more than heating part of the house).

 

[desktop987456]

See attached files; Picture 1 - Ground floor layout, Picture 2 - First floor layout:
1. Location of boiler on Ground floor
2. Proposed pipework extension - 50ft length copper pipe on ground floor
3. Radiators in (red font) to be served after extending proposed pipework; Radiators (in blue font) are being served by bigger boiler which is heavily undersized.
4. 3 radiators on ground floor with sizes (red font); similar setup on First floor (smaller radiators)
5. After extending pipework 1 boiler will cater for whole house comprising of 11 radiators.

I have calculated the required btu output of 11 radiators and is within range of boiler.
The work will be carried out by a plumber but I need to plan this properly as skilled folks are difficult to find where I live. Thanks for all your help and guidance.

 

[MNW67]

Under your avatar it says you are in Pakistan. I'm just intrigued about what the climate is like and the construction of your house. Naively, I've always imagined it being very hot, but I've just read that there are extremes.

P.S. Did you mean 3200 sq ft in your OP?

 

[desktop987456]

Again without a lot more detail it's hard to assess your scheme. It sounds like rather a large house, just adding a pump may not solve anything. This 'plumber', is he the only one quoting? Is he planning on insulating the link 22mm tubes?
Is there any zoning or other control gear on the system? (At the moment, you can heat the extension completely independently of the rest of the house- different times, different temperatures. Without some zone valves or smart radiator valves you will lose that control, heating the whole house will always cost more than heating part of the house).

I have used him on some other plumbing work elsewhere and he seems reasonable. He will insulate the proposed 22mm pipes.
No zoning or other control gear, no TRVs installed. Its a simple 'plain vanilla' system with no bells and whistle of modern heating.
I inherited the system and I am fine tuning it after recent gas price hikes. Thanks again for your guidance and help.

 

[desktop987456]

Under your avatar it says you are in Pakistan. I'm just intrigued about what the climate is like and the construction of your house. Naively, I've always imagined it being very hot, but I've just read that there are extremes.

P.S. Did you mean 3200 sq ft in your OP?

Indeed I am in Islamabad, Pakistan. Its a vast country and I am in Northern part which is much cooler in winter months. As you move towards southern part or coastal areas it gets warmer. Temperature these days in Islamabad is 5-6DegC.
It is 3200 sq.ft, I have mistakenly said 320sqft in my original post.

 

[MNW67]

Indeed I am in Islamabad, Pakistan. Its a vast country and I am in Northern part which is much cooler in winter months. As you move towards southern part or coastal areas it gets warmer. Temperature these days in Islamabad is 5-6DegC.
It is 3200 sq.ft on one floor.

Thanks, that's very interesting. I'd also be interested to know what your house is built from and how it is insulated. Are you familiar with UK construction methods? Most houses here are built from two leafs of masonry, with a cavity in between, which contains the insulation. But please ignore if I'm being too nosy!

 

[desktop987456]

This is an old house with no insulation whatsoever. Standard brick and plaster walls and no cavity walls in between, single glazed aluminium slidiing windows, Solid wooden doors. Islambad has extreme weather or contrasting weather, it gets very hot in summers and temperature gets as high as 45degC and in winters; Dec-Feb it stays between 0-10degC.
Modern houses being built are insulating their properties but older ones are very poor in insulation and you get quite a bit of heatloss in winters and heatgain in summers!

 

[MNW67]

Dec-Feb sounds a bit like here! Although we had two cold weeks before Christmas where it was about -7C at night in much of England.

Have you thought about retrofitting insulation, on either the external or internal walls? Is the roof insulated?

 

[desktop987456]

Yes, it gets cold here in these months and without insulation it gets much colder inside houses!
Adding insulation is on my to do list but it is going to be in future sometime. The house orientation is 40ft by 80ft and I am covered by neighbours walls on 80 ft side so that is a bit of insulation from neighbours. I need to add insulation on outer walls of 40ft side from front and back; a friend suggested adding a layer of gypsum on outer or inside walls once but I haven't given it much thought. The roof is not insulated but I have 11kw solar panels installed on it if you consider it much of an insulation!