replacing conventional boiler

[andy333]

We're installing a new boiler as the old one is 30+ years old (Ideal) and has slowly died over the past year or so. The house is a 4 bed bungalow. The current boiler is in the basemant/cellar and is a conventional low gravity system. C/H and H/W are needed for 11 radiators (6 downstairs, 5 upstairs), 1 kitchen, 2 bathrooms (1 bath, 1 shower). There are 2 water tanks in the loft. We've had a few quotations for the work and the reason I'm posting is that we're not sure what to go with.

The quotes we've had for the work, including vat, range from £2460 (Ideal Icos) to £3288 (Vaillant Ecotec plus 438) with a Worcester (forgotten model) for £2895. A second fitter came round and recommended the smaller ecotec plus 428 instead. I've read on this site that the Ideal Icos is not considered as reliable as the vaillant so we've ruled out the icos. My questions are:-

What size of boiler do we need? ex/ 428 or 438 if we choose the vaillant
Would a system boiler be better?
Do the above quotes sound about the right price?

Thanks in advance for any advice.

Andy

 

[gas4you]

The Vaillant 600 series system boiler is much better than the 400 series open vent.

The system should last longer as it is sealed.

Unless you have massive rooms and radiators I would be surprised if you needed more than an Ecotec Plus 624.

You need to measure your rads and then look in a rad catalogue for heat outputs. Add them all together and add 3-4Kw for the hot water.

failing that what size is your boiler now?, 60, 70 80,000 btus etc?

Does your property get warm enough now? Have you had cavity insulation done since this old boiler was installed?

80,000 btus' =24Kw, 100,000 = 30Kw in round numbers

With the Ecotec Plus range your installer can range rate the boiler to exactly suit your system during commissioning.

Can't really comment on the prices as we can't see the job, but for a straight forward job I would expect the Icos price for the Vaillant (boiler only change)

 

[keego]

I personally wouldn't rule out the Icos as I think they are a good boiler....considering it's an Ideal. Now if it was an Isore, sorry Isar then I would steer well clear.

 

[andy333]

Thanks v much for the replies.
I've done a few sums to try to calculate the required btu output. Based on radiator size/model this came to about 65000 btu for the whole house. I decided to do the sum based on room size as well and this came to 52000 btu. If I allow 3 to 4 KW for hot water as suggested, a 24KW boiler should still be enough. Does that sound right?

No cavity insulation done in answer to that question. We've tried to find the current boiler output but it's a fossil - can't find where it's indicated.

Thanks for the suggestion of having a system boiler instead. It does sound sensible. Not sure why the 2 c/h fitters who did the quotes did not suggest that so we will need to ask them.

My main query now concerns the price of the boilers. When I look at the break down of the quotes provided by the c/h fitters, the c/h fitter is charging circa £2000 for the boiler, circa £400 for materials and circa £850 for the work.
I've seen the same boiler for £800 on the web. Is there any reason why we can't buy the boiler ourselves, saving £1000+ and just pay to have it fitted etc. I can't understand why the charge for just the boiler itself is so high? Is that just so they make more profit, is it to rip me off or am I missing something here in terms of what's included and what's not.

Depending on the answers I get, I might be reaching for the credit card and buying the boiler over the phone and just paying for the work. Any opinions anyone?

Andy

 

[Nixt]

My main query now concerns the price of the boilers. When I look at the break down of the quotes provided by the c/h fitters, the c/h fitter is charging circa £2000 for the boiler, circa £400 for materials and circa £850 for the work.
I've seen the same boiler for £800 on the web. Is there any reason why we can't buy the boiler ourselves, saving £1000+ and just pay to have it fitted etc. I can't understand why the charge for just the boiler itself is so high? Is that just so they make more profit, is it to rip me off or am I missing something here in terms of what's included and what's not.

Depending on the answers I get, I might be reaching for the credit card and buying the boiler over the phone and just paying for the work. Any opinions anyone?

Others have given their technical opinion. Advice on financing the project is not what this site is supposed to be about. You should debate that with your installer.

 

[bengasman]

presuming you want to get into the 21st century and install a combi, you will need at least 35kw to run 3 bathrooms. the system of heat sizing rooms only applies to really large properties and conventional boilers with tanks and cylinders and that sort of outdated stuff. make sure the gaspipe is large enough; unless the boiler is very close to the meter, you will need 28mm supply. vaillant or worcester are the brands to go for if you want trouble free heating and hot water. the best quote will not always get you the best installer, ask people whose opinion you trust for a recommendation

 

[Agile]

Thanks v much for the replies.
I've done a few sums to try to calculate the required btu output. Based on radiator size/model this came to about 65000 btu for the whole house. I decided to do the sum based on room size as well and this came to 52000 btu. If I allow 3 to 4 KW for hot water as suggested, a 24KW boiler should still be enough. Does that sound right?
Andy

The advice is that you only allow 2 kW for water heating! Thats for a conventional system with a heat only boilers and a cylinder! So an 18 kW boiler will be adequate.

My main query now concerns the price of the boilers. When I look at the break down of the quotes provided by the c/h fitters, the c/h fitter is charging circa £2000 for the boiler, circa £400 for materials and circa £850 for the work.
I've seen the same boiler for £800 on the web. Is there any reason why we can't buy the boiler ourselves, saving £1000+ and just pay to have it fitted etc. I can't understand why the charge for just the boiler itself is so high? Is that just so they make more profit, is it to rip me off or am I missing something here in terms of what's included and what's not.

Andy

The installer makes his money on the boiler AND his installation charge. I can assure you that he will not install at the same cost if you provide the boiler. Tell him his installation cost is acceptable but you want to provide the boiler yourself and tell us what he says ( if its printable ! )

And if you have three bathrooms a combi will hardly run two and certainly not three. A basic combi is 24 kW and that just runs one so you would need 48 kW for two and a massive 72 kW for three !!!

Tony

 

[andy333]

Not sure where I said we had 3 bathrooms. Only 2 last time I counted!

Thanks for the info otherwise. Useful forum this.
Agile, that makes sense regarding installation costs. I'll ask them how much installation only is if we buy the boiler separately. I expect you're right and it will be much more. I don't have a problem with that if that's the way it works and we'll probably just go back to the original quotes and get the one person to both supply and install the boiler.

We've decided against a combi so it's going to be either a conventional or a sealed system. We will probably just take advice from the installer on whether sealed or conventional is best for us.

Quick question regarding wattage. We've had conflicting info both from the quotes received and also on the replies here in that 18kw, 24kw, 30kw have all been recommended.
Question:Is there any harm in having excess power in the boiler unit?

At the moment, a sealed system with Vaillant ecotec plus 618/624/630 makes the most senses to me as gas4you suggested.

Andy

 

[gas4you]

As I said in my post, if you go for the 24Kw the installer can range rate it down to suit your system.

I always add 3 - 4 Kw for hw cylinder, but if you only need 18Kw and are not planning any extensions etc in the future stick with this.

You can always time the hw to come on 30 mins before the ch first thing in the morning as this is the only time the boilers full output will be required usually.

 

[Agile]

The main problem is that if the boiler is over sized for the system it will be running at less than its minimum power capability for much of the time.

The full output is only needed when its -1°C outside which is virtually never. The hot water is only heated for 35 minutes after you have use it all.

Most boilers can only modulate down to 33% of their maximum so when the house is hot and its 14°C outside very little power is needed to make up the losses, perhaps just 4 kW for example. An 18 kW unit can go down to 6 kW and will switch off for three minutes every nine. A 24 kW unit would be off for four minutes every eight. Cycling on/off is rather less efficient.

There is no advantage over sizing a boiler, it just reduces the overall efficiency.

Tony

 

[Softus]

it will be running at less than its minimum power capability for much of the time.

That's clever.

 

[Agile]

it will be running at less than its minimum power capability for much of the time.

That's clever.

Its called time division multiplex!

On:Off with a variable mark space ratio and the output is integrated by the long thermal time constant of the radiators.

Tony

 

[megawatt]

Agile wrote:

It will be running at less than its minimum power capability for much of the time.

You mean ... The gas is actually not lit then?