Is the boiler I've been quoted too big?

[Chivas69]

HI
We are getting rid of a Ferrolli combi and want to replace it with a Worcester boiler! We used Worcesters site and got a couple of quotes!
The first guy recommended a 29cdi.
I was discussing with the 2nd guy how we currently don't get much pressure on our shower and taps so he suggested a 32cdi!
He then rang me the next day with his quote and said it would be for a 34cdi!

We have a small 3 bedroom detatched house with one bathroom! Only 7 radiators!
Would a 34cdi be too big for us?
Would this boiler cost us much more in fuel?

I've also read about how for a 34cdi the gas 22mm pipe may need to be changed to a 28mm! He made no mention of this but maybe it's because the 22mm gas pipe runs from meter to boiler in about 8 meters with only 2 90 degree bends?

Basically the two quotes are more or less the same and we'd love better flow to the taps! I just don't want any problems with gas pipes or massive bills!

Would the 34cdi be right for us?

Thanks

 

[D_Hailsham]

A bigger boiler will not give you greater pressure, just hotter water.

You need to measure the incoming cold water flow rate The best place to do this is the garden tap or the kitchen cold tap. Use a marked bucket and your watch. Time how long it takes to fill, say, 10 litres. Then convert this to litres per minute.

Multiply the result by 2.5 and you will get the minimum boiler size in kW. This will be enough to raise the cold water temperature by 35C, i.e from 10C to 45C. which is sufficient for a shower. But if you need much hotter water, get a larger boiler.

All the boilers suggested will be oversized for the heating, but that's normal if you have a combi boiler.

 

[Agile]

You have not bothered to tell us the model of your Ferolli boiler.

The larger boiler will not give hotter water, it will give a higher FLOW of water.

But thats only if your mains supply is capable of giving a higher dynamic flow rate.

Tony

 

[Dan Robinson]

As opposed to a static flow rate.

 

[Chivas69]

Thanks, the Ferrolli is a HE31c!
The water never seems to get very hot in the kitchen downstairs and in winter we basically have to have the shower on max for a good heat but not much water comes out then!
I suppose this could be from the rubbish Ferrolli?

My reason for the question really is because a 3rd guy quoted and couldn't believe he'd suggested a 34cdi saying it was way too big!

But for the same price as a 29cdi am I better off having the 34cdi? Even if nothing gets improved?

 

[Dan Robinson]

Wooshitter Botch accreditation at its finest

 

[D_Hailsham]

As opposed to a static flow rate.

Some people never learn.

 

[Chivas69]

?
Any ideas?

 

[Dean744PiN5]

?
Any ideas?

you've been asked to check your incoming flow rate, no one can advise until we have this information

a boiler can only heat a certain amount of water in any given time based on its output.

for example a 29cdi can deliver 12lpm at a 35deg temp rise meaning if the incoming water from the street is 20deg your boiler will be able to deliver water at 55deg at a flow of 12lpm.

when t is colder in winter the incoming main is colder, lets say its 10deg so your boiler will only be able to heat the water up to 45degs at 12lpm unless you turn a tap down to restrict the flow and then the water will come out hotter.

But if you open a tap on full and your actual flow is say 14lpm the boiler wont be able to heat your water up at that rate and it will come out luke warm.

This is why we need your incoming flow rate, because if you only have say 10lpm coming in there is no point putting in a bigger boiler.

 

[Chivas69]

Thanks mate, I will check this when I get home from work!