[c4mpute]

I'm not sure if you will ever see that, the EU is currently trying to band all flourinated hydrocarbons, right in the middle of the 'we all need a heatpump' run. The only "viable" refrigerants after that will be CO_2, propane and ammonia. The "viable" is in scare-quotes because all of them are kind of nasty, CO_2 and ammonia are quite poisonous, CO_2 is inefficient or unusable for the temperature range in question, ammonia is very very corrosive and propane is flammable and explosive. Maybe the US will do the sensible thing and wait it out, meanwhile buying up all the cheap, working heatpumps with traditional refrigerants.

[matheweis]

Is propane that bad? We have propane plumbed throughout houses everywhere here in the us, and while accidents happen they are extremely rare.

I would think that with a closed loop system the risk of a serious problem would be quite low.

[c4mpute]

The pressure is higher in A/C and heat pumps, and you have liquid propane in half of the system. A leak there will quickly create a huge volume of flammable propane-air-mixture at room pressure. The usual plumbing for heating and cooking is at a very low (over-)pressure, 100mbar or something, and your distribution network in town is typically at 1bar. A leak there is less bad and will take some time to fill up space with enough flammable propane-air-mixture to be dangerous, enough time to maybe sound an alarm and evacuate. Generally, a basement full will obliterate the occasional building in any case.