Decades before solar and wind took over green marketing dollars, back when environmentalists still promoted natural gas and hydroelectric power, heat pumps became an energy-saving fad.

The problem with them became evident nearly as fast as that electric car range you think you'll get - it is only under ideal conditions in a lab. So if you bought one because you were told it is "400 percent efficient", you probably also bought organic food because someone told you it doesn't have pesticides. In other words, you were just believing in magic.

A new meta-analysis of papers including, the authors believe, 550,000 statistically representative households concludes that up to 62 percent would see a drop in their energy bills by using a heat pump. That is fantastic - but like with solar panels a drop may not be meaningful to you. If you spend $15,000 on solar panels, the savings will be for the next owner, not you, and $20,000 for a heat pump will probably mean the same thing. You're spending real money that could double or triple if you invested it before you break even on that heat pump.

The authors note that cost can come down, with rebates built into the ironically named Inflation Reduction Act which led to inflation not seen since President Carter was in office. Solar panel customers are paid by a lobbyist loophole which forces utility customers to charge poor people more and a $5 trillion stimulus package that cut into everyone's earning power is no better.

Heat pumps have any number of apologists, mostly people selling them, journalists at places that sell everything as long as it is not natural gas, and people who bought them and desperately want to be right in doing so.  Those people now say, 'yeah, in the past it was a lie but today they work the way we always claimed they work' and the authors do find that newer, more expensive ones can cut energy usage by up to 31 percent. 

That's a population-level average. I have the same BMI as nearly every NFL Safety but who do you think is in better physical condition? The average man has fewer than two testicles. None of those may be relevant to you, especially worrisome if you are about to spend $20,000.

Why are consumers going to trust government employees when they lied in the past? Environmental conspiracy theorist Bill McKibben endorsing them is a giant red flag for the science community, since he pays college students to protest - sorry, he gives each protester a "grant" - in support of whatever industry is paying his mobile shell game of nonprofits that greenwash funds to him.

Just like Germany when it claimed it was moving from nuclear to solar and wind, anyone installing your heat pump will tell you to have a backup plan. Because a heat pump doesn't produce anything, it just uses energy to move heat around. So you will save $300 a year but is that worth spending $10-20,000? Maybe it is, if you are willing to spend your money to reduce greenhouse gas emissions while celebrities fly to climate conferences on private jets.

If you are in a moderate climate, and you also like the idea of that or a Generac or a pantry full of military MREs or anything else that make you feel like you have a disaster plan, get one if you have the means. Just don't expect to save the planet with it.