enters a calculation stage firstly it calculates the flow rate of the gases 136 using any one of a number of methods which will be described later secondly knowing the rate of flow of the gases the algorithm then calculates the required heater plate power 138 alternatively heater plate temperature to achieve a desired temperature humidity of gases alternatively heater plate power a relationship has been empirically determined using a humidifier and a heated conduit such as that as described in u s pat no 5 640 951 the contents of which are incorporated herein by reference the actual relationship for any other arrangement would either have to be empirically determined by experimentation or theoretically calculated for a desired temperature of gases exiting the humidifier of for example 37 u00b0 c the relationship between the power supplied to the heater plate p hp the rate of flow of gases f gas and the ambient temperature t amb is graphed in fig6 from this an approximate general algebraic equation has been extrapolated which the controller can use to determine an approximate level of power to apply to the heater plate p hp u2212 0 1239 u00d7 t amb 5 383 u00d7 f gas u2212 0 3112 u00d7 t amb 10 738 thirdly the algorithm calculates the required power input to the conduit heater wire 140 to deliver a desired temperature.