Even in areas where natural gas is much cheaper than electricity?
There are additional savings if your gas furnace is the only gas appliance in your house and you can remove gas service entirely, saving the monthly customer fee.
However, we put in a gas combi-boiler for hot water. Since we were renovating a townhouse, it was easy to throw in some radiant heaters on all floors. It’s a quiet, comfortable heat. I have the heat pump set to assist if the temps drop below 68F inside. All that said, insulation and air sealing is by far the most important thing to do first.
FYI: I checked the specs on my unit. It claims a 3.3X COP. So that’s $3 per therm, same as gas.
Now a question to address is whether your radiant heat is actually getting 95% efficiency. If you have an old radiator design system that was converted to using a condensing boiler, it may not be designed to keep return temperatures low enough for the boiler to operate at maximal efficiency. (old boiler systems were designed to keep the return water supply hot to prevent acidic condensate from eating the heat exchanger. This is the exact opposite of what you want with a modern system, where the return water needs to be cold enough that the flu gases condense into it to recover heat.)
If you have a way to monitor the return water temperature into your boiler, you could check. You need the return water to be below about 100 Fahrenheit in order to have 95% efficiency.
this sucks, because gas _should not_ be that much cheaper than electricity, but for subsidies or other market altering shenanigans.
It's easy to think of negative externalities and ignore positive externalities (or vice versa), but accurately summing these up is very difficult.
It is the discrepancy between market equilibria and total social cost/benefit that creates the theory of externalities. But my point is that actually determining social cost/benefit requires very extensive knowledge of all the social benefits and costs provided by something. For example, if you were to ask me what the positive externalities of clean drinking water are, I'd say they are enormous. But I couldn't really give you a number, and if anyone tries to give you a number, they are lying. But that is why I support subsidizing access to clean drinking water, rather than letting the market sort it out. It's just too valuable.
When we are talking about things like energy or transportation, they generally have enormous positive externalities, which is why they are historically subsidized. For example, even if you never use a road, you benefit from the stores you buy from having access to roads so that goods can be delivered to them more cheaply. But it's even more subtle, because cheaper transportation means bigger markets. One of the reasons why local businesses historically opposed the construction of roads is that it would force them to compete with other businesses along the same road. If most people had to walk, then they get a captive market. As soon as you introduce roads, prices come down, and quality increases because lots of little monopolies are destroyed.
So even if you never leave your house and only shop locally, you are getting huge financial benefits from cheap transportation. Thus there is a positive externality. This is why we don't mind that trucks cause most of the damage to roads but don't "pay their fair share" of road maintenance costs. It's because those trucks create enormous positive externalities by making all the goods we buy much cheaper, even if we ourselves never hire a truck. This is also why many nations subsidize railroads, bridges, roads, etc. The internet also has this aspect of enormous positive externalities. And when you are talking about energy -- it's the basis of modern civilization. Again, if you never use any energy yourself except wood that you chop down, you benefit from all the others who provide you with services having access to energy.
Now I'm not saying that natural gas only has positive externalities and that there are no negative externalities. What I'm saying is that no one can tell you what the net is, because these are things foundational to our economy and have profound effects on everything else.
So I would not try to use the logic of externalities when talking about these foundational technologies. Externalities makes sense if you are using a lawnmower and it annoys your neighbors, so you let them bid on how much you need to pay them in order to keep using the lawnmower. In very simple models, it makes sense. In the real world, it almost never makes sense, and ends up being a type of economic smokescreen for what is basically politics choosing winners and losers based on arbitrary or cherry picked criteria.
So my recommendation is to not try to use "externalities" as a justification. Here's what I would argue, for example, when I am dictator. We want to transition to nuclear power and away from natural gas. So let's tax natural gas and use the money to pay for nuclear power so that it becomes cost competitive with natural gas, and then let's reserve natural gas for things nuclear can't do for us -- such as creating fertilizers. See what I did there? I made my actual motivation the main cause and didn't invoke any economic theory of externalities. Because overall goals should not be slaves to economic models, but rather the economic models should be servants of the overall social goals. The economic model can tell you how much to tax natural gas so that nuclear becomes cost competitive. But whether to decide to switch away from one source to another requires wisdom rather than brute force calculation of all outcomes -- there is no economic model that can spit out the answer. We should not give economists that type of power.
You talk about how certain goods are immensely beneficial to society, but that’s not sufficient to claim there are positive externalities. Your example of a road being used by a store that you buy from is a poor example. Those transportation costs would simply show up in the cost of the stuff you buy (disregarding government subsidies for roads, of course, but that’s a separate issue).
However that's not the policy we are pursuing. We are pursuing very blunt instruments to try to discourage investment in developing natural gas fields full stop. Which is bad public policy.
The other issue is by raising the price of natural gas, we are raising its price for all uses. And the price of natural gas tends to determine the price of fertilizer, which tends to determine the price of food. So this policy makes food more expensive.
Even worse, natural gas and things like coal and oil are in some sense substitutes. Not perfect substitutes, but what happens when we make oil more expensive is that people shift to coal and natural gas to generate energy, and so these two become more expensive as well. Similarly, if we were take all coal offline, that would increase demand for natural gas and oil as substitutes, and again, the price of these commodities would rise, which would increase the price of food.
What would be nice would be to see if we could de-couple these prices somehow -- e.g. tax usages of natural gas downstream of the price of the commodity itself. Other ideas are also possible.
It’s shocking it’s not a bigger delta the other way.
Hotter water means a more reactive system and smaller radiators (you'll need five times the volume for a given power output when you compare plumbing water of ~30 to 70+. You are almost certainly not installing that. Maybe you are installing floor heating, in which case you are likely OK.
But most people I speak to don't realize that 1. Gas efficiency goes up as temperature differential goes down, and 2. energy transfered to water also needs to leave the system at your radiators. So size them for the effiency you want, or be disappointed with a significantly higher gas bill.
Gas furnaces are dead simple, and still break and require maintenance. Heat pumps, more so. Generators? By far the most.
Combining the three sounds like a huge headache for marginal efficiency gains.
As far as efficiency gains, we're talking 25-40% of the energy being produced as electricity and the majority of the rest being turned into hot water for residential use, either by one household or a whole city block. This doesn't sound like a terribly marginal gain. Specially if the energy production is done during the hours when traditional solar installations are not producing which are generally when folks are running their heating.
The working temperatures of ammonia are probably wrong for a heat pump, but perhaps something similar could be devised.