Installer recommends 18kw instead of 15kw?

[D_Hailsham]

On what basis?

1. The OP says: Never had any problems with the 15kw Potterton in terms of power.

Why should his requirement suddenly increase to 18kW?

2. The installer says it's worth paying a little extra for the 18kw because it will be more efficient - something about the fact that it will run more smoothly when it steps down to a lower output than the 15kw which will switch on and off.

That would be true if the installer was comparing the modulating WB with the ON/OFF Potterton. But if you are comparing two modulating boilers, they would both be running at exactly the same output (provided it's within the modulating range of the boiler). So if the max requirement is 15kW, the 18kW boiler will be running at 15kW, just like the 15kW boiler. At the bottom end, if the requirement is 5.5kW, the 15kW will modulate down to 5.5kW. While the 18kW will have to run in on/off mode as it can't modulate below 6kW

3. This is the opposite of my understanding, that the 15kw boiler is more efficient than 18kw since it burns less fuel.

The OP is confused. If the immediate requirement is, e.g. 11kW, both boilers will modulate to 11kW. So, give or take a small difference in efficiency (output/input), both will be consuming virtually the same amount of gas.

I agree that it's up to the OP to tell the installer what he wants. The installer could always get the client to sign a waiver, exonerating the installer of any liability if the boiler subsequently proved too small.

 

[D_Hailsham]

Duplicate post

 

[bernardgreen]

Same fecking piece of schit boiler anyway with a different coding chip.

Could the price that the installer pays be the same for both the 15kW and the 18kW and by selling the 18kW he gains an extra £60 profit on the supply of the boiler ?

 

[Agile]

I am always suspicious when I see anyone trying to sell something which is not the obvious solution.

But sometimes some boiler installers don't seem to fully appreciate the importance of matching a boiler power to the application.

It is very common for boilers to be fitted with a power output higher than what is needed.

 

[Agile]

Worcester are about the only manufacturer who produce a range of small heat only boilers with a wide range of power outputs so they can be well matched with the demand.

Other manufacturers seem not to be interested in making small output boilers. Even though they make up a good proportion of boilers needed.

Intergas have produced a very reliable boiler but don't sell a low power version in the UK for some reason.

Tony

 

[FiremanT]

Why would I *trust* a tradesman who I have never seen before? Trust is something that is earned. I might trust him in the future,

And yet tradesmen are expected to immediately trust a customer?
We invest a lot of time in quoting a job, buying the gear, and spending time installing it. And trust that the client is going to pay the agreed fee at the agreed time?

 

[bernardgreen]

Intergas have produced a very reliable boiler but don't sell a low power version in the UK for some reason.

Do they sell a low power version other than in the UK ?

Can the standard Intergas heat exchanger be run at lower power levels and still be "efficient" or do they produce a smaller version of their heat exchanger fpr lower powered boilers ?

 

[JohnD]

Once my house is heated up, the steady usage is about 12kW when 0C outside, typical for a winter's day, which is about what the "boiler size calculator" says, and it runs very quietly.

But more than that on the rare occasions when it is -10 or -15

However, if I have been away and the house has cooled down, the boiler runs at a greater rate for a while. For the first ten minutes or so it might use double that to get all the radiators hot, then slowly modulate down.

The old one was 15kW unmodulated, and on a cold night you could feel the house cool down if you ran a bath and it had to reheat a cold cylinder.

I wouldn't want to splash out on a new boiler that couldn't cope with unusual winter spells.

So I don't see a problem with having a slightly oversized boiler. The price difference here is negligible.

 

[tibi08]

And yet tradesmen are expected to immediately trust a customer?
We invest a lot of time in quoting a job, buying the gear, and spending time installing it. And trust that the client is going to pay the agreed fee at the agreed time?

You are confusing trust with business risk. Tradesmen shouldn't trust any customer, what basis would they have to trust them? But they have to take a risk that the customer won't pay, in order to carry on their trade.