If you take 1 unit of gas and burn it you get ate 1 unit of heat
If you take 1 unit of gas and make electicity in a power plant you get 0.5 units of electricity and can make that into 1.5 units of heat
If you take 1 unit of gas and make electicity in a small home generator you make 0.1 j it’s of electicity and make 0.3 units of heat
The ratios are likely to be off on the specifics but that’s how a heat pump powered by grid electicity from grid gas is better than gas directly and gas directly is better than a local generator.
Firstly, consider the capital costs of an engine + natural gas pipeline + heat pump (excluding electrical motor) versus either a natural gas pipeline + burner _or_ a heat pump + electric motor. A high guess on the lifetime of a suitable natural gas engine under consumer quality maintenance (variable and generally late) would be 10,000 runtime hours. On heating duty cycle that's about 5 years. You can reduce runtime hours with more starts and stops, but that reduces the engine life -- probably more than it saves.
So the extra capital costs of the engine must amortize over five years out to less than the lost efficiency. Importing electricity has economies of scale in capital costs. Direct burning of natural gas has low capital costs.
Secondly, there's the efficiency question. A moderate-sized heating system has a peak power of around 100,000 BTU/hr or about 29 KW. That's about 37 horse power. Engines of that size are piston engines with around 20% efficiency. Therefore out of every 5 units of fuel-heat you get 1 unit of mechanical energy you have 4 units of waste heat. That mechanical energy put through a heat pump will net you around 3 units of heat for a total of 7 units of heat for every 5 units of fuel.
That's better than just burning it, but 140% thermal efficiency is only ~45 points better than a natural gas furnace and comes with much higher maintenance costs (oil changes, filters, etc.).
Importing electricity has economies of scale in production, even if generated using natural gas, because the 'engines' are of more efficient types with 40-60% thermal efficiency. Further, an electric motor is low maintenance and long lasting. So for every 5 units of fuel-heat in a power plant you can get between 6 and 9 units of heat through an electrical heat pump. Not too different overall, but with much lower per-house capital and maintenance costs.
So compared to a natural gas furnace it's not a win because of the capital costs and maintenance costs versus the much cheaper equipment; a ~$3000 engine every five years is $600 per year, which buys a lot of natural gas. Compared to an electric heat pump it's not a win because the efficiency of engines that small aren't great.
But a renewable energy powered heat pump is better.
It’s more about utilities taking on the difficult work of making electricity greener (I recently learned California burns a substantial amount of natural gas for electricity production! But at least they are able to continually pick up the solar percentage in the daytime) and homeowners taking on the work of making their own consumption cleaner.
Also it’s a natural security measure to try to reduce reliance on fuels that we may need to import one day.
https://www.epa.gov/chp/what-chp
That being said, I’d much rather leave electricity generation to a utility, maintaining generators is expensive and you’re screwed if your primary generator goes down without utility backup power or a secondary backup generator.
Since large centralized power generators are much more efficient, yet still put out prodigious waste heat, why not use that waste heat to heat homes?
You get the benefits of an electric heat pump while recovering a large portion of the plant's waste heat.
District heating plus heat pumps is probably the most efficient you can make a combustion plant.
Once we get off of fossil fuels, we can recover waste heat from industrial processes, or convert the district heating system to be purely electric or concentrated solar or something.
Because the vast majority of the waste heat created by the relatively inefficient generator would be used for heating the home, the electricity produced is nearly free. If you run the heat pump compressor directly from the engine, even more so.
The main caveat is that the generator (which would need to be a well insulated, liquid cooled type) would be expensive and would require rebuilding every 10000 hours or so.
The efficiency of a small generator is about 1/2 of that of a power plant, but between harvesting 90percent of all waste heat and having no distribution losses, the fuel consumption cost would typically end up lower than the electricity cost of an all electric system.
This co-generation design is actually pretty common here fuel oil is the main heating fuel, but it should work even better on gas.
https://www.robur.com/en-us/applications/solutions/solutions...
I have seen reports (do not have reports to link to sadly) on massive losses in the pipe infrastructure.
While there is loss in the electric grid too, at least it wont contribute to more emissions, as well as probably being overall less costly than the lost gas.