Boiler or balance?

[Aloysius]

We have moved into a large house with four floors and sixteen radiators in total (many large double ones). It is a relatively new installation with a Worcester 24i system boiler. The problem we have is that the two radiators on the top floor do not get more than lukewarm even with the TRV fully open. One of the radiators on the floor below is similar (a little warmer but not hot).

I have bled the radiators
I have ensured the boiler is pressurised
I have tried adjusting the boiler temperature setting
I have tested the three radiators in question by turning off all the others in the house. In this situation the three radiators heat up fully and cool down again when the other radiators are turned up again.

So what does this leave me with? Is the boiler sufficient to heat this large system (although at least three or four radiators are set low or switched off)? Or is the answer likely to be that the system needs to be balanced somehow? Are there any other possibilities or tests I can carry out?

Thanks for any advice received.

 

[Dan Robinson]

Balance or maybe a bigger/extra pump.

 

[Aloysius]

Is there any concern that the Greenstar 24i system boiler would not be big enough?

 

[D_Hailsham]

Use the Whole House Boiler Size Calculator to check if your boiler is correctly sized.

Use Stelrad Catalogue to find out the heat output of your rads. Page 50 left column Stelrad Catalogue. Page 50, left column, is the typical steel rad.

Provided the boiler is correctly sized, it doesn't matter if the rads add up to more. It's actually better as it means they can run at a lower temperature and still provide the necessary heat. It's when the rads are too small that you have to be concerned.

Check how far open the lockshield valves are - they are the ones at the other end from the TRV. If they are more than one turn open from closed (same as a tap) the system has probably never been balanced.

 

[jackthom]

Is there any concern that the Greenstar 24i system boiler would not be big enough?

If the water in the pipe on the return feed to the boiler feels warmer than the troublesome radiators then there is some sort of balancing or flow problem.

OTOH if that isn't the case and the boiler is still running flat out after some time with relatively cool pipes on the return feed, the boiler may also be overstretched.

 

[Agile]

It would need to be an amazing huge detached house to need 24 kW of power.

Obviously its never been balanced!

If a Victorian terrace then may need about 13-15 kW if the lost insulation is reasonable.

Tony

 

[Aloysius]

It's a pretty big five bed Victorian semi with a number of large single glazed windows, so not at all energy efficient I fear. The boiler is in the converted basement, and the problem radiators are three floors up from there. I have read that the boiler pump should have different settings which can be tried, but I see nothing in the manual about that. Does any know?

 

[Agile]

In that case then it could need perhaps 18-20 kW.

With the cost of gas its sensible to improve insulation! Particularly in the loft!

Are all the five bedrooms really being used and so need heating?

Do you really need to heat all the bedrooms during the day?

How many zones do you have?

 

[Aloysius]

I have tried the boiler size calculator, which told me I need a 48Kw boiler

This was worked out by applying the footprint of the house to all four floors. In actuality, the basement and top floor are a fair bit smaller, so three floors is a more reasonable calculation. This still estimated me needing a 37Kw boiler.

In terms of use, the basement and top floor would normally have heating on very low (partly to avoid any damp issues) but it would be nice for the top floor rads to produce good heat when they are needed (eg when guests stay in winter).

Other than the basement which retains heat well, the rest of the house is very drafty and hard to heat. There is no loft insulation potential as the top floor is bedrooms in the attic.

 

[Agile]

Hailsham is the expert on heat calculations but 48 kW sounds way over the top!

The first thing to do is balance the system!

Then to measure the flow and return temps!

If it really needed 48 kW then can you afford gas bills of £4000-£6000pa?

 

[Aloysius]

If it really needed 48 kW then can you afford gas bills of £4000-£6000pa?

I think I will be sticking with my 24i, even if it's too small!

Another silly question, but best I check. I have assumed that the problem top floor radiators are only costing me for the heat they are producing. In which case, the fault isn't so bad as on full they are only as hot as I would normally set them (ie low). But is there any reason why it might be more efficient for them to work properly (following balancing I assume) and then turn them down to the same required heat?

 

[Agile]

You only pay for the heat that you use.

But for when you do need comfortable temps its useful to have them balanced so you can turn them up.

Tony

 

[Dan Robinson]

A rad only needs to be warm enough to do its job.


Look out for a by pass valve that is poorly set.

 

[D_Hailsham]

I have tried the boiler size calculator, which told me I need a 48Kw boiler

This was worked out by applying the footprint of the house to all four floors. In actuality, the basement and top floor are a fair bit smaller, so three floors is a more reasonable calculation. This still estimated me needing a 37Kw boiler.

Can you post the data you used, then I can check the calculation.

 

[Aloysius]

I have tried the boiler size calculator, which told me I need a 48Kw boiler

This was worked out by applying the footprint of the house to all four floors. In actuality, the basement and top floor are a fair bit smaller, so three floors is a more reasonable calculation. This still estimated me needing a 37Kw boiler.

Can you post the data you used, then I can check the calculation.

Semi-detached house in Northern England, mix of wood frame single and double glazing, two 6m walls ( front and rear) and one 12m side wall, pitched roof with limited insulation, no wall cavities or loft insulation, four floors (although both basement and top floor are perhaps 60% of the house's footprint), no extension, 3m ceilings on ground floor, but lower on other floors (perhaps 2.6m on first floor, and 2.1m in basement and attic).

I may have misunderstood the hot water allowance. I left it at default.

EDIT: I have tried redoing it a few times and keep getting slightly different results, but all in the low thirties Kw. I must have used the wrong figures initially I guess.