The main thing I'm looking at is eliminating CO2 emissions as best I can. I'm not in control of them all, but where I am in control I'm working to eliminate. Bottom line is that we need to get emissions to zero as fast as possible. With that in mind, the energy cost of new appliances that are run on renewable energy pays dividends before those appliances are at end of life, and existing working gas appliances fall into a sunk-cost fallacy IMO.

It doesn't matter if I have 1 GW of solar and batteries and EVs and the whole grid is converted to renewables and I only eat vegan from my own back yard, etc. If my home furnace runs on gas it's emitting CO2 to run. There was literally an exhaust pipe running out the side of my house for the furnace, water heater, etc. The only way to eliminate those emissions is to eliminate the appliance.

I don't know what the break even cost on all this stuff is, because I frankly don't care. I did do the math on the heat pump water heater vs. what we were paying for the gas water heater (there was a time where the water heater was the only gas thing running), and the new water heater saved us about $30/mo in energy costs just comparing gas to electric. And with solar panels the savings over a gas heater are even greater. I figure break even on a very high end water heater is <4 years.

[edits because I mixed up answers to another comment]

Why do you personally care about eliminating CO2 emissions?

In addition to the obvious point mentioned in a sibling comment (existential threat to humanity)...

Switching to zero-emissions alternatives now means less adjustment later when the polluting versions are (hopefully inevitably) banned.

When they are banned however there will likely be incentives, cheaper prices and better technology. Switching now makes even less sense.

Tragedy of the commons right there.

Granting your premise, it's still not a problem upon which individual actions like this have any impact whatsoever. What OP does with his house, heating it with gas, electric, wood, or coal is not going to matter one bit on a global scale.

There are almost zero people on the entire planet whose personal impact is noticeable at this scale. But so what? We need both individual and policy action.

“At scale, nobody notices the harm I’m doing” can be used to justify all manner of antisocial behavior. I don’t buy the argument.

Existential? As in humans go extinct? I’m going to have to ask for a source.

> If for environmental reasons I feel like removing working appliances is counterproductive

I don't think this follows. There's not THAT much that goes into making a furnace, but it emits a hell of a lot of emissions every year that it's running. I suspect they paid back the CO2 cost of the new equipment relatively quickly.

Didn’t OP mention this was all tied up in a remodel? If so, makes perfect sense to do this all at once.