If you have the owners manual, look on page 31 for the correct specification. According to that they claim the correct fuse is a fast blow ceramic 1.6 amp fuse rated at 250 volts. I simple terms, Here is why.
According to Ohm’s Law watts/volts= amps.
(1) The Smoke Fire, according to Weber is rated @100 watts, although the average watt draw on the SmokeFire is around 85 watts.
(2) The unit operates on normal house voltage of 120volts, (not 240 or 250), but nominal is closer to 110 to 115 volts. So let’s say 115 volts.
(3) Therefore: 85/115= .74 amps, or 100/115=.87 amps.
(4) However, house voltage can vary to as low as 110 volts, or lower at the SF plug when you use an extension cord, plus on start-up there is always a minor, instantaneous current in-rush or surge. Hence, Weber decided to use a 1.6 Amp fuse, which could handle such circumstances and made it a fast blow to protect from power surges. This gives you up to around 192 watts @115 volts (assuming you are actually getting that voltage at the SF unit) before the fuse blows.
(5) As for the 250 volt rating of the fuse, that means it can handle the normal variations in power supplied by your utility (I monitor mine continuously, and it varies between 111 and 118 volts) across a typical day depending what other loads are being exerted on the pole mounted utilities transformer that also services my neighbors). The key is that it will blow quickly at wattage that exceeds 192.
(6) The model number of this fuse is a 5x20MM. The five is not an amp rating, because a 5 amp fuse at 115 volts would not blow until it sees a 575 watt draw from the SF, which would “fry” the unit since it is rated at only 100 watts. 5*115=575 watts.
Bottom line: only replace your fuse with a 1.6 amp, 250 volt fast blow ceramic fuse, or F1.6A250V