Replacing old Ideal Mexico RS50 Boiler

[vaultsman]

Good Evening all,

1st time here...and no expert!...so please be gentle!

I'm looking to replace an old Ideal Mexico RS50 regular boiler with a system boiler. The RGI (who works mainly in industrial/commercial) who'd do the work likes Main boilers...but also Worcester. He's an ex-neighbour of mine.

According to the info plate on the old boiler, the RS50 is rated at 14.7 kW max, but the smallest SEDBUK A Main system boiler (ECO) I can see is rated 24 kW. Are these boilers modulating? Or is 24 kW much too oversized?

The property is a 1930's 2-bed semi and, from a quick calculation at Replacement Boiler Size Calculator , a 15 kW boiler seems about right.

I'm (probably) tending towards a Worcester 15i or 18i instead.

Any help and guidance gratefully received!

 

[AllyBongo]

Vaillant eco boilers can be range rated to suit your needs. All boilers modulate now

 

[vaultsman]

Thanks AB,

Does that mean that Main boilers can't be range rated? And does range rating affect efficiency significantly?

 

[AllyBongo]

Dont know about Main's. But Vaillants can defo be altered 1Kw at a time. Good boilers too

 

[tamz]

All A rated boilers will modulate down to suit the load (some lower than others) so there is not really a need to range rate anymore.

 

[vaultsman]

Thanks tamz,

So there's generally not really an efficiency penalty in oversizing?

 

[Steve @ TheHeatingHub]

dont forget you need to allow for the pipework + cylinder in you calc. I tend to go with 5000btu+15000for a standard cylinder on top of the heat requirements.

 

[tamz]

Thanks tamz,

So there's generally not really an efficiency penalty in oversizing?

Not really as long as you don't go totally over the top. Check the boiler MI's and it will tell you the minimum rating. A worcs 18i for eg will modulate down to 5.54kw and the 24 down to 7.38. Remember the load will decrease as the system heats up and trv's start closing.

The worcester Ri boilers are regular boilers so you would need an external expansion vessel and pump. Their system boilers are i system.

 

[vaultsman]

Not really as long as you don't go totally over the top. Check the boiler MI's and it will tell you the minimum rating. A worcs 18i for eg will modulate down to 5.54kw and the 24 down to 7.38. Remember the load will decrease as the system heats up and trv's start closing.

The worcester Ri boilers are regular boilers so you would need an external expansion vessel and pump. Their system boilers are i system.

Thanks again tamz,

The spec on the Main 24 Eco gives heat outputs (condensing) as 8.37 kW min and 26.95 kW max...so I'm thinking that minimum figure could be a tad on the high side as the load drops?

If I do go for the Worcester, yes, I'd probably plump for the 18i.

Cheers,