While non-condensing boilers just exhaust these gases, and waste the included energy, condensing boilers re-use the contained energy by condensing the water vapour this makes them around 10% more efficient than a comparable non-condensing system. Depends on how big your property is - i think combi's were originally invented for use in flats although am sure they have moved on by now. Got something that’s not an emergency? call us anytime on. We are experts in installing condensing boilers.