: I can give you my thoughts, and what I consider the “pro’s” and “con’s”, but I don’t know of anything that would support a definitive answer for you.
First, everyone today has to consider economics. I don’t know where you’re located, how much your building will have to be heated during how much of the year, or what your utility rates are for gas and electricity, but your Consulting Engineer should certainly be able to give you an economic comparison, and that’s what drives most of these kinds of decisions today.
Second, I’m wondering whether there is any possibility of using Heat Reclaim from your Data Center to provide some energy savings for the rest of the building. Again, your Consulting Engineer should be able to tell you if this is worthwhile considering or not, and what the payback term would be for the investment.
Third, is the matter of dependability. Since this decision apparently won’t directly affect the Data Center (which normally won’t require heat except possibly in a generator or battery room), it probably doesn’t really matter, but at least may be a consideration if one or the other is historically more dependable in your area. And if you might one day expand the Machine Room into part of the extra 6,000 sq. ft., gas might help you maintain heat when electricity is shut down in that area for construction. Just a small additional consideration.
Fourth is the question of potential contaminants. Again, this should really not be an issue if a gas heating system is properly designed, since I would not expect there to be direct combustion devices in the occupied areas. So long as the furnace chimney carries byproducts away from the Data Center and the building air intakes (which by Code is must), there should be no concern about contaminants entering the computer room.
Last is just the matter of comfort level. Some people have concerns about gas in their facilities because of the remote possibility of a leak and explosion. If you consider this a legitimate concern, then go electric. If not, then evaluate all the above and make your decision. Other than our overall responsibility these days for energy conservation, there really is no right or wrong decision in this regard as far as I’m concerned.