Short Cycling Efficiency - Mod-Con versus Conventional

SpeyFitter

We've all seen the graphes of a boiler's efficiency versus it's firing time as far as short cycling is concerned. We've all been made to understand that the nice long burns give a conventional boiler better efficiencies as well as reducing emissions.

But how do mod-cons do in short cycling scenarios? Do they get up to efficieny much faster in short cycling situations or do they take as long or longer than conventional machines?



One scenario for you:

Lets say we had a house with a 55,000 BTUH input cast iron boiler (80%) and a 50,000 BTUH fixed fire input (90%-ish) condensing boiler (not modulating, or, lets for arguments sake say the 50,000 BTUH is it's low firing rate). Which boiler will take longer to get up to it's efficiency? (I used 55,000 versus 50,000 to assume similar output with respect to their efficiencies).