10. Installation – flue connectors (a) fluing off the top. Fluing straight off the top gives the best possible draught performance and is to be preferred where the chimney performance is suspected of being sluggish. It is the safest bet for boats & caravans where the chimney has to be short. XXTop fluing assumes that (a) the chimney can be swept 'from the top down' (i.e., the preferred way,) and (b) the stove permits access for soot removal. (Some stoves can be awkward – particularly if fitted with a boiler near the top.) XXThe other thing to consider in this arrangement is flame impingement. The manufacturers of twin-wall stainless steel flues are at pains to point out that their systems are designed as 'vents' rather than as combustion chambers and should not be exposed to extreme temperatures for lengthy periods. XXIf your stove has a short flue path there is some danger that flames may enter the first section of chimney in which case it would be prudent to install a short length of cast-iron or VFP (vitreous flue pipe) before continuing to build up in stainless steel. In most cases 600mm should be adequate – anything longer may cool the flue gases which is undesirable. XXIt is generally safe to build a stainless-steel flue straight off the top of a cooker, since the lengthy flue passages in these appliances makes flame-impingement less likely.