Pipework advice - 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.

 

[gmartine]

1. Difficult to say without seeing the layout but I suspect the most convenient option would be the way to go with a correctly sized pump.

2. Shouldn't be if system design is correct.

3. If the boiler has been correctly sized the only reason to run two boilers is for redundancy and if you'd prefer say independent hot water provision.

 

[Knappers]

Maybe this time it's best to get a decent engineer in, to do it right!?

 

[Desktop987456]

Maybe this time it's best to get a decent engineer in, to do it right!?

In my area where I live it is difficult to get heating engineers! To make client comfortable and no complaints they just oversize everything here at customer's expense and ignorance, they did this to me when they installed the system and now they want to sell me one of their fancy boilers.
My boiler works well, I only use 3 to 4 bedrooms so I won't be using all 6 bedrooms.

 

[Desktop987456]

3. If the boiler has been correctly sized the only reason to run two boilers is for redundancy and if you'd prefer say independent hot water provision.

We don't use all 6 bedrooms but one of the upstairs bedroom which is in our use is connected with small boiler., with current energy prices it doesn't make much economic sense to run boiler to heat one bedroom. I have the front boiler running constantly so to gain efficiency I was thinking of connecting this bedroom or all 5 radiators (connected to the smaller boiler at the back with the bigger boiler).
For hot water we are using electric geyser since I have 11kw solar panels installed.

 

[Desktop987456]

I have asked two plumbers for quotes; one is saying copper at 20mm and the other is insisting on PEX 20mm. He says that he can lay copper pipe but elbows will restrict the flow of water hence PEX is better? Any advice or suggestions? Thanks in advance.

 

[DAVE the old git]

I for one would not use PEX Pipe even if they were given it away Would always use copper but its expensive or failing that 26mm multilayer pipe might be the way to go . one 30KW boiler is more then enough to heat 12 Rads But in order to save yourself money this heating system needs to be Zoned Running two boilers is costing you money The attic or roof space has to be lagged 30% of your heat goes out through Attic. At the very least I would separate up stairs from down stairs including hot water All gas appliances have to have the necessary Gas at any gas boiler to work efficient under size gas to a appliance is what you do not need As regards the extension i would run separate pipe work for these rads Depending on how many rads that are involved again i would also zone this extension All rad circuits controlled by room stats Hot water controlled buy Cylinder stat failing that the combi boiler takes care of the hot water then you can either have the other zones controlled by motorized valves and room stats But if this home has no controls its cycling on the boiler stat which in itself will just rob you this is a given . What you do not want to do is to heat any space that you do not use

 

[Desktop987456]

I for one would not use PEX Pipe even if they were given it away Would always use copper but

Thanks Dave for your thoughts. I am going to use copper 20-22mm depending on cost. My plumber is saying that 15-18mm should do the job but I am insisting on using 20mm to the very least.
By extending the pipework; 2 pipes for flow and return, should be enough to cater for 5 radiators.
Existing boiler has 5 radiators with a total load of 14 kw (~50k btu).

 

[Ric2013]

55kW sounds a lot for 3200 sq ft (you wrote 320 sq ft, but I'm assuming that's a typo), unless that's 3200 per floor? I'm tempted to agree with your calculation of 35kW.

To put your boilers into context, there's a Victorian house I've worked on which has 13 radiators, and an internal floorspace of 3282 sq ft (total walkable internal area). Cavity wall and loft insulation, but weird shape with a lot of surface area and not especially airtight. Some of the windows are old sliding sashes, but most have internal secondary glazing. It has a 24kW boiler for heating and hot water purposes. The boiler is certainly not undersized. This is in Colchester, so not much colder than London. The boiler is also a heat only with a vented cylinder.

 

[Desktop987456]

55kW sounds a lot for 3200 sq ft (you wrote 320 sq ft, but I'm assuming that's a typo), unless that's 3200 per floor? I'm tempted to agree with your calculation of 35kW.

To put your boilers into context, there's a Victorian house I've worked on which has 13 radiators, and an internal floorspace of 3282 sq ft (total walkable internal area). Cavity wall and loft insulation, but weird shape with a lot of surface area and not especially airtight. Some of the windows are old sliding sashes, but most have internal secondary glazing. It has a 24kW boiler for heating and hot water purposes. The boiler is certainly not undersized. This is in Colchester, so not much colder than London. The boiler is also a heat only with a vented cylinder.

Thanks Ric for your comments. I have attached floor plan with covered area of my property. I apologize for the typo but this is the total area of the property and not the covered area, the covered area for two floors (Ground+First floor) is 4500 sq.ft. with no insulation cavity walls, single glazed aluminium windows. Your example of old victorian house fits perfectly with mine!
I have separate arrangement for hot water so boiler is for heat spacing only. My btu or kw requirement of the property is what I have currently installed in terms of radiator. I had a room upstairs that took ages to warm (see attached layout) so I realized that radiator is not putting up with the heat requirement of the room so I upgraded it with a double panel and it is working perfectly now. I have to tee off a 22mm connecting from flow but I am working which is the best location to tee off; from Upstairs flow line or downstairs line where boiler is installed.

 

[Desktop987456]

I took the plunge on Sunday on extending and connecting my pipework from front boiler. We layed the 50ft length of 20mm copper pipe (.8 inches inner dia), my pipe work is 20mm going out from boiler and then

reduces to 15mm going into radiators in each room. After extending the pipework to 50ft, I split the pipes going on back side rooms and upstairs and made two zones by installing a manual valve. I am not utilzing downstairs rooms at the back so we shut off the valve. I had doubts that I may need to install a pump as it may not cope up with the requirements of upstairs rooms but to my surprise the upstairs bedrooms heated up quickly than front ones despite running 50ft from boiler to the back and then further 10ft upstairs. The boiler now has 12 radiators connected to it.
I haven't tested the other zone (downstairs) yet but boiler is consuming more gas; it stays on for 10 minutes and then off for 5 minutes, previously it used to stay on for 6 mins and then off for 8-10 mins.

One issue I see is that the plumber made a connection to 50ft extension first on the flow and return line coming from boiler; so it is heating more quickly but others are taking time (front side rooms upstairs and downstairs).

Question : Should I install a bigger pipe 25mm or 1inch inner diameter pipe coming out of the boiler and then make connections to newly installed pipes and others which are 20mm now? So I can get even flow to all the radiators.
Thanks

 

[gmartine]

You should be able to balance the radiators manually to ensure they roughly heat up at the same rate. Your plumber should be able to do that.

 

[Desktop987456]

but boiler is consuming more gas

Thanks as always for your help. My central heating system is working fine now, the radiators are balanced. I have noticed that boiler is staying on or lit longer; about 12 minutes on and 8 minutes off so it cycles 3 times in one hour.
Before this extending pipework, my gas usage was 0.9units per hour but it has gone up to 1.5units per hour? The sensor that controls the burner is attached with Return pipe. Would it make any difference to attach it with flow pipe? Just thinking that with this recent extension of pipework the returned water to boiler is taking a lot longer so burner is staying on a lot longer?
Any clues or pointers? Thanks

 

[gmartine]

Increase in gas use sounds about right doesn't it? To improve efficicency and therefore consume less gas lower the flow temp as much as possible to be comfortable which will also increase burn time but at a lesser gas rate.

Do not move the sensor.

 

[Desktop987456]

Increase in gas use sounds about right doesn't it? To improve efficicency and therefore consume less gas lower the flow temp as much as possible to be comfortable which will also increase burn time but at a lesser gas rate.

Do not move the sensor.

Its a non condensing simple boiler with two solenoid valves to control the gas flow and a bigger burner below the heat exchanger. The thermostat and its sensor is attached to Return pipe, the burner is lit at 41degC and goes off at 45degC. I was thinking that my be if I attach the sensor to flow pipe, would it change anything?

 

[ShaunCorbs]

What boiler is it ?

 

[Desktop987456]

It is non condensing locally made boiler as I am not in UK.
The return lines of the extended section (old pipwork) has lost some of the insulation material and is exposed to outside temperature, does it affect how long the burner is on?

 

[Desktop987456]

Increase in gas use sounds about right doesn't it? To improve efficicency and therefore consume less gas lower the flow temp as much as possible to be comfortable which will also increase burn time but at a lesser gas rate.

Do not move the sensor.

Thanks for your comments. The sensor was slightly off from the pipe which wasn't give accurate reading. Now sorted the sensor and gas usage on hourly basis is 1.1 units per hour which was just about what I expected after extended pipework and radiators. Thanks for everyone's help.