These heaters require a natural-gas connection and professional installation. Natural gas is almost always less expensive than propane, and you don't have to worry about running out of fuel or bother with changing tanks. The tradeoff (in addition to installation costs) is that you lose portability. If wind direction changes or you want to rearrange your patio furniture, you're stuck with the patio heater where it is. You can, however, install natural-gas "convenience outlets" that let you plug in a grill or patio heater and then move it around the patio.
The Endless Summer 233010 is a commercial-grade patio heater. We didn't find any reviews of this model, but it's the natural-gas version of a model that's an Editor's Choice at Patio-Heater-Direct.com. It's rated at 40,000 BTUs an hour but uses a relatively small 26.5-inch reflector that is apt to diminish its circle of warmth.
The Dayva Premiere Natural-Gas Patio Heater (*Est. $430), another Editor's Choice at Patio-Heater-Direct.com, is a top seller there and also highly recommended at another retailer, PatioExperts.com. This heater has convenient hidden wheels and a much larger square reflector -- 34 inches on each side. Owner-written reviews say it spreads the heat well, but some reviews complain about the rest of the heater. Both the powder-coated steel body and the screws can rust, and one owner got a heater with a faulty igniter. A version with a stainless-steel body is available (though the screws still aren't stainless) but it costs a lot more (*est. $790).
For less than that stainless-steel model you could get the third Editor's Choice gas patio heater at Patio-Heater-Direct.com. The Easy Radiant Free Standing Patio Heater (*Est. $760) comes in steel or in stainless steel for about $100 more. It carries an outstanding three-year warranty. Heat adjusts up to 50,000 BTUs an hour, and the round reflector is 34 inches in diameter. The sole owner-written review gives it a perfect rating, though noting that the control knob is a little stiff. The version with a steel base comes in two powder-coat colors, black and green.
Sunglo, the only company we found that manufactures its natural-gas patio heaters in the United States, makes two basic models with fixed outputs of 50,000 BTUs an hour. Both use 34-inch reflectors and the type of ignition experts say is by far the best, direct spark ignition. The Sunglo PSA265 (*Est. $800) is fixed in the ground for permanent installation. It comes in steel or in stainless steel for $250 more. You can have it wired to a switch so you can turn it on and off that way, but otherwise it requires no electricity. It carries a one-year warranty.