Our home has it outside, and I'd personally prefer this.
1. You dont have to bring the service man through the house, and/or be embarassed if the utility room is in a state.
2. Our service man (same for 15 yrs) calls to the house even if we are not there, and can do his thing and bill us.
3. No worry about fumes, at least inside the house.
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I don't think there's much of a difference - I'd say its a matter of Personnal choice.