Bungalow Renovation - New Heating System Questions

[Peter James]

Hi Folks,

I am about to embark on a major renovation of a bungalow we have just bought. Current size is around 1000sqf and we are extending to around 1500sqf.

We will be re-plumbing, rewiring and installing a new combi gas central heating system with all new pipework.

I will be getting a builder in to do the extension and some of the renovation, but I want to do some of the basic work myself – such as installing radiators and pipework (even if I don’t connect it all up.

I and a reasonable competent DIYer and have done some plumbing before – though no design work on central heating.

More importantly I want to know how everything works and to know enough to be able to have intelligent conversations with the professionals to allow me communicate exactly what I want in their language, but to ensure I get what I want.

So I have been think about the design of the CH and hot water systems.

I am thinking about a Worchester Bosch Greenstar CDi Classic 42CDi .

I will need 12 radiators (two of which will be chrome towel rail types in the bathroom and en-suite)

This seems to work out around 63,000 BTUs or 19kW needed. The boiler produces 30kW – is over speccing like this OK?


What I am planning for the CH pipework is as follows –

22mm Copper connection to the boiler for flow and return for 1m (WB say at least 600mm copper). Then using Hep2O for the rest.

I will have an automatic bypass valve between the flow and return near the boiler – I am thinking of using a tee where the copper meets the plastic pipe.

I will have two zones (7 radiators in one and 5 in the other). I plan to split the 22mm flow and return and run closish to each radiator. I will take a 15mm branch from the main 22mm flow and return for each radiator (so each 15mm branch will feed only one radiator).

I plan to insulate all the pipes with 25mm thickness insulation

As far and how water is concerned, the boiler has a 15mm outlet so I guess I use 15mm Hep2O all the way. I need to service hot taps in kitchen, bathroom, en-suite and utility; two showers. I think the washing machine and dish washer take only cold.

I know there are very detailed calculations that can be carries out on flow rates and heat loss – is this really necessary?

Have I given enough information to allow an assessment of whether this will work? If not, what other information do I need to work out or provide?

Sorry for all the questions.

Thanks

 

[terryplumb]

first thing you should do is find a professional who is prepared to work with a diyer on installing a system ,alongside of him.it may be a lot more difficult than you think. combi boilers struggle to provide hot water to 2 showers simultaneously. as for oncoming pressure /flow rates they must be taken into account as the entire house plumbing is dependant upon them . most combi boilers have a by pass built in..

 

[flameport]

I will need 12 radiators ...
This seems to work out around 63,000 BTUs or 19kW needed. The boiler produces 30kW – is over speccing like this OK?

If you want a combi boiler, it is inevitable that the output will be far too high, however they will operate at less than maximum.
19kW of heating appears rather on the high side. Is that 19kW because the radiators you chose happen to add up to that, or because that is the heating requirement for the building?

I need to service hot taps in kitchen, bathroom, en-suite and utility; two showers.

Do you want those hot outlets to be usable at the same time?

What is the pressure and flow of the water supply to the property?

 

[Peter James]

Thanks flame port.

n the 19kw heating requirement, this is based on the radiators I am looking at. But this is based on working out what is needed from various calculators. And I have definitely over specified as I dont want to be left short of heat (maybe this is a bad ting to do).

I dont know the mains pressure coming in. So from your question, I guess I need to have this measured?

Re the showers, it is VERY unlikely that we will use two showers at the same time as their are only two os us in the house.

The instructions on the boiler advise fitting an external bypass valve.

 

[bernardgreen]

I need to service hot taps in kitchen, bathroom, en-suite and utility; two showers.

Then you should consider a hot water cylinder and heat only boiler and not a combi.

Do the job properly and use copper instead of plastic. Might take a bit longer to imnstall but plastic can start to leak a few months after being installed apparently free of leaks. Then there is a lot more time spent foxing the leak and repairing any water damage.

I was convinced copper was best when 1) a sales rep for plastic pipe fitting admitted he would not have plastic plumbing in his house and 2) neighbours had to have their new kitchen ceiling pulled down to get to leaks in the new plastic plumbing that appeared several months later. Of course soldered copper joints can leak if not done properly but only very seldom will the joint wait several months before starting to leak.

 

[muggles]

The 42CDi only modulates down to about 10kW for heating, which means that as your house heats up it'll cycle rather a lot, using an excessive amount of gas and increasing wear & tear in the process. If you must have a high-powered combi, look at the Vaillant Green IQ 843 which modulates down to 4.3kW. This will reduce your running costs and wear and tear on the boiler, as it'll be starting and stopping much less frequently when running your heating. Every time a gas boiler starts, it uses about 70% of its full power (there are a few exceptions to the rule, but that's typical) then modulates down to the required output once the flame has stabilised. If a boiler overshoots its temperature before it has chance to reduce power, it'll go off again and then restart. This uses quite a bit more gas than a boiler which is able to sustain a lower power flame for longer.

Before specifying a high-powered combi boiler though, you first need to establish your incoming flow rate at 1 bar pressure. This is sometimes referred to as dynamic flow rate, and is measured in litres per minute. There is absolutely no sense in purchasing a combi boiler which is overspecced for your incoming main, as you can never get out more than you put in! If the incoming main isn't at or above the 18l/min at 1 bar mark, a 43kW boiler is not for you.

Pipework? Personally I think copper is proper. I have been known to use plastic on temporary connections before now, but it's always taken out and replaced before the job is done.

Go for big radiators - running big rads at a low temperature is much cheaper than running small ones at a high temperature.

 

[winston1]

Then you should consider a hot water cylinder and heat only boiler and not a combi.

Do the job properly and use copper instead of plastic. Might take a bit longer to imnstall but plastic can start to leak a few months after being installed apparently free of leaks. Then there is a lot more time spent foxing the leak and repairing any water damage.

I was convinced copper was best when 1) a sales rep for plastic pipe fitting admitted he would not have plastic plumbing in his house and 2) neighbours had to have their new kitchen ceiling pulled down to get to leaks in the new plastic plumbing that appeared several months later. Of course soldered copper joints can leak if not done properly but only very seldom will the joint wait several months before starting to leak.

There seems to be a lot of prejudice against plastic for some reason. Ten years ago soon after plastic came out I used a lot doing mods to the plumbing in the house I had just bought. Never had any of the problems you mention and I'm not even a plumber. New builds are often plumbed in plastic these days. I can only assume problems are caused by incorrect fitting.

 

[terryplumb]

new house builders are interested in what's cheapest ,and maximising profit margins, they are not interested in longevity .

 

[winston1]

new house builders are interested in what's cheapest ,and maximising profit margins, they are not interested in longevity .

Surely they have to be. New builds often come with 10 year NHBC guarantees.

 

[terryplumb]

yes they do and they are notorious for not wanting to know when you have a problem . large or small .

 

[muggles]

Surely they have to be. New builds often come with 10 year NHBC guarantees.

They do, for the fabric of the building, but as far as I'm aware the services are only a 2 year warranty. Also, the minimum claim value is £1000 and can take six months from initial contact to resolution - I know this because my sister has recently made a claim for a leaking roof.

 

[bernardgreen]

nd they are notorious for not wanting to know when you have a problem

Some developers create a new company to build a few houses and then when the houses are occupied and the owners start asking for defective works to be corrected the new company goes into liquidation and escapes all responsibility. "Sorry but we had to cease trading so we cannot help you "

 

[Agile]

Thanks flame port.

Re the showers, it is VERY unlikely that we will use two showers at the same time as their are only two os us in the house.

It is not "very unlikely" that you will use two showers!

It is just not possible because a combi boiler will not produce enough hot water for two good showers!

 

[Agile]

Surely they have to be. New builds often come with 10 year NHBC guarantees.

The guarantee is intended to only cover serious structural problems and the £1000 minimum claim will mean that most smaller problems will in effect not be covered.

In theory, a new buyer has a claim for minor defects for two years from the developer. But making a successful claim is often problematic because so many just go bust as do many contractors and builders.


I have been to a block of about 28 flats which were built with long horizontal flue runs of about 6-7 m. Unfortunately the installers did not provide any slope of 3 degrees on the flues as specified by the boiler manufacturers and many of the joints are now leaking. Because of the long flue runs there is not enough ceiling height to accommodate the correct slope. Some flat owners are trying to claim from the NHRBC but its rather more complicated because some of the flats are rented from the housing association who commissioned the building.

 

[Pin 5]

Then you should consider a hot water cylinder and heat only boiler and not a combi.

Do the job properly and use copper instead of plastic. Might take a bit longer to imnstall but plastic can start to leak a few months after being installed apparently free of leaks. Then there is a lot more time spent foxing the leak and repairing any water damage.

I was convinced copper was best when 1) a sales rep for plastic pipe fitting admitted he would not have plastic plumbing in his house and 2) neighbours had to have their new kitchen ceiling pulled down to get to leaks in the new plastic plumbing that appeared several months later. Of course soldered copper joints can leak if not done properly but only very seldom will the joint wait several months before starting to leak.

Or you could do the job in copper and make it look worse than if it was installed in plastic.