Boiler Size and TRV Info Required

[CliveDiy]

Hi Guys

Can anyone offer some advice on radiator valves and boilers, First of all can I state I shall not be installing the boiler myself, but may decide to buy it depending on what price Mr. Gasman can get me one for.

I shall be installing the radiators and pipework to them myself, there are a total of 13 radiators in a 4 bedroom detached house, which will have one bath one shower, and a total of 4 sinks throughout the house.

The first thing I would like to know is what size combi boiler to purchase, I was thinking of a Worcester Greenstar Jnr NG 28i Condensing Combi 82,000 Btu / 24 kW
11.4 Ltrs/Min or a Glow Worm Ultracom 38 CXI Digital 102,390 Btu
15.5 Ltrs/Min.

The total wattage based on -3.0c is 13810 watts plus obviously enough to feed the domestic hot water.
I’m not sure if the boilers I’ve mentioned above are way over the top or not, long before combis had been thought of it was said that boilers should not be too large for the system they were intended for as they would not run very efficiently, but I am not sure about the modern boilers of today or whether they are based more on the flow rate required on the domestic sideof things.

I don’t want to go too much over the top with radiator valve prices as I am having to totally refurbish the whole of the house not just put central heating in.
I have read one or two old articles about noise coming from valves, can anyone advise if I should go for the wax sensor or liquid sensors ones and would it make any difference regarding noise from them, I understand some of them need to be fitted the correct way around which I assume it will say on the box.
The radiator in the hallway will not have a thermostatic valve as there will be a room stat nearby.

I have also read that the pipes need to be lagged for a certain distance from the boiler, can anyone advise if this is correct.

Many thanks for any help

Clive

 

[rssteve]

see what the boiler man wants to install then get your own price, he might not want to fit a boiler you have bought.

 

[D_Hailsham]

The first thing I would like to know is what size combi boiler to purchase, I was thinking of a Worcester Greenstar Jnr NG 28i Condensing Combi 82,000 Btu / 24 kW
11.4 Ltrs/Min or a Glow Worm Ultracom 38 CXI Digital 102,390 Btu
15.5 Ltrs/Min.

The total wattage based on -3.0c is 13810 watts plus obviously enough to feed the domestic hot water.

Combi boilers are sized according to the max instantaneous hot water requirement and has to take into account the mains pressure and flow rate. It's no good having a boiler which will deliver 20 litre/min if the mains can only provide 10.

All modern TRVs are 2-way. Liquid sensors are better as they react quicker to temperature changes. Go for a quality brand such as Drayton or Honeywell.

 

[bengasman]

Would you go to the garage and tell the mechanic:
"here you go mate, stick these sparkplugs in that I got at the market; yours are too expensive."?
Only 2 kinds of installers will fit a boiler that you provide.
Those that won't try to hide their profit (and you won't get much change from a grand), and cowboys who will do anything for a couple of hundred quid.

 

[CliveDiy]

Hi bengasman

I take your point about me supplying the boiler, that’s why I haven’t rushed out to buy one yet, I hasten to say it would not be from the market if I did, in fact I was expecting to pay about £900 just to buy it.

Daft question I suppose but who do all the places sell their boilers to, only gas fitters?

I guess at the end of the day I can always fit the rads and pipework myself then just shop around for someone to supply and fit the boiler, and by that I do mean someone who is Gas Safe registered.

 

[CliveDiy]

Hi Hailsham

Thanks for the info on boiler sizing and explaining about the wax sensor v liquid ones, I was thinking about getting the Drayton valves, they look neat compared with some of the others which are available.

If you read my reply to bengasman, I may not have to worry about boiler sizing, although I could phone around a few gas fitters and find out if they are prepared to fit a boiler supplied by me.

 

[BingoBongo]

its not just the boiler they will be wary of.

have you installed rads/pipework before???

the may not want to take reaponsability for your mistakes/if any

 

[CliveDiy]

Thanks for your reply BingoBongo

Yes I have fitted them before and if there is anything wrong naturally I would not be expecting the gas fitter to accept responsibility at the end of the day I guess its not much different to having a boiler upgrade to an existing system, I would only expect the fitter to accept responsibility for his own work and not that of someone else or something which is already in existance.

 

[bengasman]

Most suppliers supply to anyone who pays them for goods.
Your idea is rather common, and the questions you should ask yourself are:

Is there something like a free lunch? The cost of a boiler installation for a RGI is x, whatever x may be.
Some will massage the figures by charging you 0.3 x for the boiler and 0.7 x for the work in order to make it look like they are working for a very modest amount. If you take away their 0.3 x profit, they will either have to come up with extra cost, or charge you more for the labour, or cut corners, or simply work for less. The latter will not happen.

The second is: how on earth would I be able to buy a boiler for less as a one time purchase than somebody who buys 20 or 50 every year.
I guess the answer is obvious.

 

[CliveDiy]

Thanks for your answer bengasman

As I said, I will fit the rads and pipework myself and then shop around for quotes to supply and fit the boiler by someone who is gas safe registered.

I’m not really bothered how the price is calculated either by putting the extra on the labour or on the cost of the boiler, I’m just interested in the overall figure and believe me I’ve had a fair variation in figures quoted for other jobs which I have had done by qualified registered people, just because one person charges less than another within reason and both are registered does not make one of them a cowboy.

It could be that one company carries more overheads than another hence the difference in quotes, but I don’t really want to get into all of that, I was just after some diy info which is why I came on here in the first place, so my thanks once again D_Hailsham for your information on the stats and flow rate of the boiler.