For indoor home emergency I use one of these;

http://www.gasproducts.co.uk/acatalog/Natural_Gas_Double_Gas_Boiling_Ring_with_FFD.html

to boil water I would use a Simplex No4 Kettle (the one with the built in heat exchanger base). The heat exchanger on the base of kettle makes all the difference in increase efficiency by a wide margin. The Esbit and Primus Etapower pots are also extremely efficient at transferring the heat to the water.

http://www.simplexkettles.co.uk/acatalog/Standard_Kettles.html

When using a standard 15Kg LPG bottle this will allow me to boil approx 1.25 metric tons of water.