Method for calculating size of boiler in an unvented system.

[muggles]

Got mine from

http://www.johnsonandstarley.co.uk/products.asp

Yes, you probably did, but not everyone is a muppet

 

[muggles]

Ah right. I used their website as a way to see the outputs of various boilers on offer.

Many advise to not oversize the boiler, but others imply it should be.

But really, what I want to know is, are the calculators I was linked to earlier, about right for a 1-2 bedroom, stone wall cottage (with dimensions I posted earlier), when they give recommendations of 6.13KW & 6.8KW?

Don't know, you entered the figures and the result is only as good as the figures put in, but they're reasonably close to each other and so likely to be pretty accurate

It's not a case of oversizing the boiler as such, just choosing the most appropriate one for your application. The minimum output is as important as the maximum in your case

 

[bernardgreen]

Yes, you probably did, but not everyone is a muppet

My J&S boiler makes me a warm and happy muppet.

 

[Agile]

With a small property with a low heat loss then its even more important to have a boiler which is not overpowered.

12 kW should be totally adequate.

But also important is the minimum power output. The boiler will only need to be working at 2-3kW much of the time so the minimum on/off modulation is best.

Many calculation sites INCLUDE the 2kW for hot water already and don't need it added separately.

I have fitted quite a few Worcester Ri heat only series and have found them pretty good really. Many other makers don't make the lower power models.

Tony

 

[D_Hailsham]

With a small property with a low heat loss then its even more important to have a boiler which is not overpowered.

12 kW should be totally adequate.

That will leave about 5 kW for heating the cylinder. Is that enough?

If we assume a 150 litre cylinder with an appropriate coil, it will take approx 95 minutes to heat it from 15C to 60C. That reduces to 40 minutes if HW has priority.

If HW is timed to be permanently on, so it is only controlled by the HW thermostat which will have a differential of about 10C, reheating the cylinder will take 21 mins or 9 mins with HW priority. But you then may be reheating the cylinder unnecessarily.