The 300% is closer to an average. When it's over 40F you'll reach over 400% efficiency. Now a question to address is whether your radiant heat is actually gett

The 300% is closer to an average. When it's over 40F you'll reach over 400% efficiency. Now a question to address is whether your radiant heat is actually getting 95% efficiency. If you have an old radiator design system that was converted to using a condensing boiler, it may not be designed to keep return temperatures low enough for the boiler to operate at maximal efficiency. (old boiler systems were designed to keep the return water supply hot to prevent acidic condensate from eating the heat exchanger. This is the exact opposite of what you want with a modern system, where the return water needs to be cold enough that the flu gases condense into it to recover heat.) If you have a way to monitor the return water temperature into your boiler, you could check. You need the return water to be below about 100 Fahrenheit in order to have 95% efficiency.