Which is more sustainable and causes less potentially environmental impact? - a electric or gas fire?

Question

Gas as a fuel generally costs less, but what other long term, greater considerations exist?

I also want opinions:

What are the general pros and cons between gas fires; fluless gas fires, and electrically fuelled radiant fires; electric heaters with fans.

Which kind of fire is generally safest?

Do flu-less fires eliminate the risk of odourless carbon monoxide poisoning?

Are the general potential explosion and asphyxiation risks greater than potential hazards using electric fires?

Which would need safety servicing the least?

Basically:

What would be the best an that an wealthy urban landlord, claiming to offer "Value, Integrity and Environmental Stewardship", could offer tenants?

NB

Fires serve as a back-up to gas C/H heating system or for for less intense interseasonal heating - (No garden or wood available).

& Gas fuel, as in the UK meaning; Natural Gas, methane, not petroleum, or oil based fuel.

Answer 1

One would think electricity causes the least environmental impact but, this is incorrect unless the electricity produced for the heating system is environmentally friendly, i.e. wind or hydroelectric generators. Methane would be the best alternative fuel because it can be obtained from many sources particularly decaying organic material. As for the safety of your tenants if you provided gas furnaces with electronic ignition devices instead of "pilot lights" you would be providing them the optimum of safety and economy as well as being environmentally efficient.

Answer 2

Gas is the most efficient heating. Electricity is not well suited to heating and is much less efficient for that purpose. Also, if ice brings down the power lines gas usually still works, unless your heater has an electric fan that needs to be on when the heater is on.