Ideal Minimiser FF80 Problems/Replacement

[XrayDave]

Hi Tony

Do I gather from your post that you DO install boilers?

If that is the case, what advice or comments can you offer on:

a) Worcester Bosch Greenstar 30 CDi (or 24i System boilers)

b) Vaillant ecoTech plus 600 series (probably the 624 System boiler)

and

c) Remeha Avanta Plus 24s System Boiler

Is there much to choose between these boilers?

Is one make significantly more efficient or reliable or significantly cheaper?

Thanks in advance

Dave

 

[XrayDave]

It's worth finding out the rad output as it might have a bearing on the size of boiler and could affect how well your house heats up. Please use the link I gave and post the results.

Hi again D_Hailsham

Have done quite a bit of maths working out the radiator outputs due to the age of the system (25+ years) as the Stelrad link you gave me only has a few similar products. The figures below represent my "best educated guess".

Most of the original radiators are double panels but un-finned, plus we have a large heated towel rail in the bathroom which is plummbed into the central heating.

Anyway, here are the figures:

Adding in, say 2kw for hot water and a bit for future upgrading (Bed 4 is usually quite cold - 2 external walls and solid concrete floor), this looks like a 24kW boiler is required.

Opinions?

Dave

 

[D_Hailsham]

Have done quite a bit of maths working out the radiator outputs due to the age of the system (25+ years) as the Stelrad link you gave me only has a few similar products. The figures below represent my "best educated guess".

Adding in, say 2kw for hot water and a bit for future upgrading (Bed 4 is usually quite cold - 2 external walls and solid concrete floor), this looks like a 24kW boiler is required.

Assuming your figures are correct you have about 22kW of rads plus 2kW for hot water cylinder.

Now for more maths and blinding with science

Rad outputs depend on three temperatures: Flow in, Return out and Room. All rad data is published based on standardised temperatures: Flow = 75°C, Return = 65°C, Room =20°C. Modern condensing boilers use a temperature differential of 20°, so then the flow is 75°C the return is 55°C. Unfortunately this reduces the radiator output by about 15%, so your 20.325kw rads only produce 17.4kW of heat.

Luckily this is OK as you only need 13kw for heating plus 2kW for hot water, so a 15 or 18kW boiler will be just fine. It just means that your radiators will be able to run at a lower temperature and still produce the necessary heat.

 

[XrayDave]

Thank you D_Hailsham for all of your help today.

I did take note of the warning at the top of the database "Small differences in the calculated SAP seasonal efficiency values are not significant and should not be relied on when comparing boilers." but thanks for pointing out that small differences in quoted efficiency walues are meaningless.

Dave

 

[Agile]

Its not clear to me how you have worked out the heat outputs of your rads! You cannot say a 600 x 1000 is the same output as the same size with no fins.

I agree the total boiler power needed is about 15-18 kW.

I mostly repair boilers but am qualified to fit them and do fit several each year.

There are many boilers on the market and they mostly have a few advantages and many disadvantages. Generally the Viessmann and Vaillant are the best in the highest price tag and the Biasi the best in the budget priced range.

Warrantee is important and the five years for Viessmann is good. Installers fitting only Worcester or vaillant can sometimes get 4 or 5 years but they will not be able to discuss differing models without being biased. Thats something that I can do.

Spares are important too. Vaillant and Biasi are well stocked at merchants but Viessmann ( and Remeha ) are only available from their factory.

Customer service is also important as few installers are able to do warrantee repairs for you. Worcester is tops for this whereas Vaillant are bottom as they dont answer their telephones for tech advice.

There are too many variables for a householder to consider and that means that I can go and discuss individual needs from an informed position. However, unlike many installers who wonder where their next job is coming from, I dont go to visit to give free advice! I give budgetary quotes over the phone but charge to visit and produce a specification that can then be bandied around to search for the lowest price from a non registered third world installer.

Tony

 

[XrayDave]

Hi Tony

As far as estimating the radiator outputs went, I took the base data from the Stelrad site.

I looked at their K2 radiators for those that are double & finned and took their output directly when I had the correct size.

For the older (imperial-sized) radiators (which are mostly double panel, unfinned), I took the data for the P1 radiators (single panel, unfinned). I then had to do some maths.

I looked at the outputs for single panel, finned (K1) and double panel, finned (K2) for the same size of radiator and averaged the results over several sizes. The double panels' output (on average) is 1.83x the single panel.

I then took the P1 figures (single panel, unfinned) and scaled the output according to the size and then applied the 1.83x factor for a double panel unfinned. Got to be the best estimate with the data I have to hand.

For the heated towel rail, I found the output for the same towel rail from the Wickes website - although the model shown is chromed and ours is white enamel. Again, it has got to be fairly close.

My house is large (3 floors and 14 radiators) and most of the radiators are double & unfinned, so I reckon that the load figure of 20kW is not too far off. Floor area around 200 m² and volume around 530 m³.

Certainly, when I ran the sedbuk and EST calculators, I thought that the figures of around 15kW for the boiler size was too small - given that our current, 11 year-old, condensing boiler puts out about 27kW.

OK, I know that boiler technology has advanced in the last 10 years, but the current boiler cannot be too far off the mark surely?

Dave

 

[D_Hailsham]

I looked at the outputs for single panel, finned (K1) and double panel, finned (K2) for the same size of radiator and averaged the results over several sizes. The double panels' output (on average) is 1.83x the single panel.

I then took the P1 figures (single panel, unfinned) and scaled the output according to the size and then applied the 1.83x factor for a double panel unfinned. Got to be the best estimate with the data I have to hand.

I think you are wrong in assuming that, because K2 rads give 83% more heat than a K1, a double P1 will give 83% more than a P1.

Using the 600x100 as an example: P1 = 610W, K1 = 1000W, P+ = 1409W and K2 = 1778W. So adding fins to a P1 (i.e K1)gives a factor of 1.64 (1000/610) and adding a second unfinned panel (K+)gives a factor of 2.31 (1409/610). It could then be argued that 64% of the heat from a K+ comes from the fins. so the heat output of a double P1 will only be 2.31/1.64 = 1.41

My house is large (3 floors and 14 radiators) and most of the radiators are double & unfinned, so I reckon that the load figure of 20kW is not too far off. Floor area around 200 m² and volume around 530 m³.

But it is very well insulated. Was there any insulation, double glazing when the original boiler was installed?

Running the figures through Sedbuk we find this: if your house had no insulation and single glazed windows it would require 28.4kW; loft insulation saves 4.2kW; cavity insulation saves 7.2kW; double glazing saves 2.2kW. This means a fully insulated double glazed house only needs a boiler output of 14.8kW.

I am not surprised by this as my present house house has an oversized boiler for the same reason. When it was put in there was minimal loft insulation, maybe 25mm, single glazed windows an no cavity insulation. The boiler installed was 15kW. The house has been updated over the past 20 years and now has cavity and loft insulation and full double glazing. According to Sedbuk it only needs a 7-8kW boiler.

The house maintains a constant daytime temperature of 21C yet the rads hardly get above 60C, which shows that the room thermostat is cutting off the boiler before the boiler thermostat.

 

[Agile]

Your Minimiser is a 24 kW boiler with a typified flow rate of 80°.

Potentially it can give a higher output if its fully condensing but thats not going to happen ( return lower than 55° ) unless its in the start up mode with a cold system.

Just because the boiler may be able to give 24 kW it does not mean that your system is needing all this power. I would not expect it to.

Any replacement should be matched to the actual heat loss required. Rad outputs will be lower because of the lower flow temps from current boilers.

An old double panel had very close panels and will be a lot less than twice a single panel, perhaps 1.2 or 1.3 times?

I think that you are very lucky because a 15 kW or 18 kW boiloer will probably be sufficient and you have good rad sizes and good insulation.

Tony

 

[XrayDave]

Thanks for the input guys.

Running the figures through Sedbuk we find this: if your house had no insulation and single glazed windows it would require 28.4kW; loft insulation saves 4.2kW; cavity insulation saves 7.2kW; double glazing saves 2.2kW. This means a fully insulated double glazed house only needs a boiler output of 14.8kW.

This 14.8kW figure is what I get from sedbuk too.

The house is fully-double glazed, has cavity wall insulation and a minimum of 100mm rockwool loft insulation and about 1/4 of the loft has 180mm of rockwool.

But it is very well insulated. Was there any insulation, double glazing when the original boiler was installed?

By "the original boiler" I presume you mean the one that has just broken down DH? The house had full double glazing & cavity wall insulation, but the loft was poorly insulated - about 25mm glass fibre insulation ove about 1/2 the loft area with about 100mm of Rockwool on the other half (it was a work in progress).

With the Ideal Minimizer, the radiators were hot to the touch - I'm guessing at somewhere between 50 and 60˚C and the boiler thermostat was in the middle (settings 0-6, it was on 3). Most of the time the boiler was running when the room stat switched the boiler off.

For a better estimate of radiator output, rather than my figure of 1.83, would a figure of 1.5x the Stelrad P1's be closer to the mark?

I'll run the calcs again using this figure to see the heating load & then post on here again.

Thanks once again.

Dave

 

[Agile]

You should not confuse the heating load of the rads and the house heat loss!

The boiler should be rated to match the house heat loss.

If the rads have a higher capacity thats all to the good because it will increase the efficiency of the boiler's operation as it will increase the amount of condensing.

Tony

 

[XrayDave]

You should not confuse the heating load of the rads and the house heat loss!

The boiler should be rated to match the house heat loss.

Tony

Thanks Tony,

So, I should go with the figures from sedbuk and/or EST calculator ie 15-18 kW?

Coincidentally, I've just recalculated the "best guess" radiator load and it comes out at 17.75kW

So, if I factor in say 2kW for water heating that gives me just under 20kW.

Therefore, I'd need a boiler with an output of around 24kW??

Have I understood this correctly?

Dave

 

[Agile]

Over rating your boiler reduces efficiency.

All these calculators are only approximate.

I would take 15 kW, add 2 kW for water and reach 17 kW and then look for an 18 kW boiler!

Too many installers and most homeowners think its better to have an over powered boiler.

That causes short cycling and longer warm up times. Even good installers sometimes dont seem to appreciate this.

I have been to several three bed semis where they have bought a 32 kW boiler which causes many problems. Its like talking to the deaf trying to explain the problem to a householder when half of the installers dont understand!

Tony

 

[D_Hailsham]

By "the original boiler" I presume you mean the one that has just broken down DH?

Yes.

With the Ideal Minimizer, the radiators were hot to the touch - I'm guessing at somewhere between 50 and 60˚C and the boiler thermostat was in the middle (settings 0-6, it was on 3). Most of the time the boiler was running when the room stat switched the boiler off.

If the boiler was able to keep the house warm with the boiler stat set to the middle, that shows the old boiler was oversized. A boiler is sized for a worst case situation, normally outside temperature of -1C. At this temperature the boiler should be delivering its maximum output, which means the flow temperature will be at the highest. If you can keep your house warm in the current cold weather with the flow temperature at 60C, the old boiler is oversized.

Assuming the flow temp is 60 and the return 50, the rads will be giving out about 62% of their stated output. So your original 20.33kW becomes 12.6kW and 17.75kW becomes 11kW. Both of these are close to the 13kW Sedbuk and EST recommend (2kw of the 15kW is for hot water).

 

[Agile]

Exactly!

I once fitted a 24 kW boiler in a six bedroom detached house and the heating was fine and the boiler would cycle off every 15 minutes for about 3-4 minutes when it was freezing outside.

Only problem was I chose an ideal Isar which was not the best choice of boiler but then we did not knwo just how unreliable they were going to be.

Tony

 

[XrayDave]

Thank you both.

You seem to be agreed that an 18kW boiler should suffice - we'll see if British Gas agree!

So, I'm looking at

1) Worcester Bosch Greenstar 18i (or 30 CDi System Boiler)

2) Vaillant ecoTech plus 618 System boiler

or the

3) Borag Remeha Avanta Plus 18s System Boiler

Given that my mother values customer service, it will probably be the Worcester Bosch given that there is little to choose from the three of these boilers.

Thanks for being so patient and taking the time & trouble to guide me through this.

Dave