Boiler sizing advice required

[Londonguy]

Hi All,

I've had a number of heating engineers visit and received differing opinions, so would like some advice before I choose a plan of action.

I moved into a large 1930's semi detached (over 2,000sq ft) that had been extended with a two floor extension six years ago.

We found that the radiators are warm (not hot to touch) at the top and cold at the bottom (all 19 radiators). Also, the house never managed to heat up to 18 degrees so the boiler never switches off (24 kW system boiler), my gas bills are very high. The house is solid wall but the extended part is cavity wall insulated.

I've been told that I need 30kw by some engineers and a 37kw valiant boiler by others. I have 19 radiators in the house which is large and have a 120 litre non vented water cylinder.

What is the right size? Is there a logical way to calculate it (some of the links I've found no longer work)?

Any advice great fully received.

 

[Dan Robinson]

Various methods of sizing are out there.

The most annoying being the Whole House Method. But it might be enough to get you started - it all depends on your budget. I would say thought that 24kW is likely to be fine in terms of output; however, your pump and control arrangement might leave a lot to be desired.

It would help to tell us more about what you have in this respect, rather than being all Billy Big Balls about the size of your London house (for those of us that cover London, 2000 feet is nothing more than "sizeable" .

Funnily enough, I am pricing some remedials for a very similar sounding place - although they have a 300 litre cylinder and Underfloor heating downstairs, robbing flow from teh top floor rads. They're looking at about £900 to rectify via a LLH and additional system pump.

 

[Londonguy]

Hi Dan,

Sorry that you interpreted my post as being "billy big balls" I thought it would helpful to provide the size of the property as it may affect sizing requirements.

I'd really appreciate it if you could let me know specifics of what further detail would be helpful as I'm no heating expert?

Thanks

 

[Dan Robinson]

Sorry that you interpreted my post as being "billy big balls"

Sunday evening banter mate - don't worry.

Need more information of your system really.

 

[Agile]

As a very rough calculation check, I find that 100w/sq m gives a very useful figure.

That gives 20 kW.

We don't know about your loft. Loft insulation gives a lot of reduction to the heat requirement as 25% of heat can be lost from an uninsulated loft.

But 24 kW should be more than adequate.

But the system must be capable of getting the heat to where it is required.

You didn't bother to tell us what boiler you have but I suspect the current boiler is almost certainly adequate with the correct setting and system adjustments.

Tony

 

[Londonguy]

Hi

@Dan - I apologise, I'm usually overly sensitive by the time Sunday evening roles around, ha ha.

@tony - we currently have a Glowworm 24hxi. The new part of the house is properly insulated in the loft though the original part of the house has been boarded down in the loft area so suspect not great for insulation, though great for storage.

 

[Agile]

Although I am not greatly impressed by your boiler model, but if working it should have a totally adequate heat output for your house.

Tony

 

[BigSnoopy01]

i would be looking at the system design if the rads are not getting the rooms warm.

 

[Londonguy]

Hi Tony,

The problem is the boiler seems to work at full tilt constantly, it just never gets the radiators warm enough to heat the rooms.

 

[simond]

If the boiler never switches off - a key part of your post - it is undersized. And since you mention that the rads don't get to full temperature, that, combined with the boiler never switching off raises alarm bells for me.

However, it is possible that your boiler isn't working properly. I went to a house for a boiler quote a few years back where BG were the maintainer. They'd been cold for 3 yrs and BG had changed the pump and room stat. Their boiler never turned off.

I measured the gas rate at the meter, 2 minutes later we knew that the boiler was running at around 6Kw instead of 24Kw.

So the first thing I would would do is run the system and measure the gas usage at the meter, there are some cheap apps that can do this easily.

 

[Londonguy]

Unfortunately the previous owners have laid beautiful hard wood flooring all over the house so I can't pull up the floor to have a look at the system design without wrecking the place.....a limitation I know.

 

[Agile]

I dont think that YOU should be planning to look under floorboards!

I think that you should be planning to call a professional to check the boiler heat output and the balance and see exactly what is wrong.

Tony

 

[Londonguy]

Hi Tony, I completely agree though I've had a few professionals in recently and the reason for my confusion is the different opinions/advice I've received from each. I thought the advice would be consistent but it isn't.

 

[Dan Robinson]

Many ways to shave a cat I'm afraid, but there are several things to try before pulling out a working boiler (first being, as said, it is working correctly).

 

[simond]

https://itunes.apple.com/gb/app/ideal-gas-flow-rate-calculator/id507399951?mt=8

No floorboards to be lifted, just get the app (this is one of many) and look at the gas meter. Simples.

If the boiler stays on for hours at a time it's either too small or it isn't using enough gas.