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Comment by ashayh | Hacker News Reader

The article mentions the most important point towards the end: “The better you insulate, the less heat you need in the first place,”

No heat pump will help if your house is leaky or under insulated.

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I have new heat pumps in a very old, under insulated, and leaky house. I didn't use my oil furnace last winter (the first since two additional pumps). My costs were about half of the previous year, and I'm sure my carbon footprint was much better as well.

Can you say more about what your comment is supposed to mean?

Not OP, but my assumption is that better insulation means you need less heating and cooling.

I've lived in a home with a literal hole to the outside. During the winter we had to run the radiators non-stop and it was still freezing.

If you are trying to save energy, then sealing up and improving insulation will generally have the largest bang for the buck.

They mean that your bill and footprint would have been even lower if it were better insulated and less leaky.

Our house (in Europe) is relatively old and not well insulated by modern standards, and all of the advice we read and receive from experts is that heat pumps are not a good fit without additional insulation.

The gist is that we’d need to spec larger units and/or run them harder than usual, removing savings vs. gas.

Isn’t insulating a house way more expensive than buying a bigger heat pump and paying for extra electricity?

It probably depends on what kind of insulation work needs to be done.

My parents' house in France is one of those hundred-year-old stone ones. It's fairly cool in the summer, but it gets quite cold in the winter. My father did the insulation work himself (he's not in construction) for fairly cheap and saw his gas bill halve.

The usual other option is to look at increasing the size of the radiators, then you can lower the flow temperature and you still get big efficiency savings.

It doesn't really matter. You should insulate anyway to save energy, but a heat pump will still use 1/4 the energy as resistive electric for the same heat. Depends on your gas prices as to whether it's worth it, but it almost certainly would be.

A worked example - In AU gas is metered per MJ - 3.6MJ/kWh. So 3c/MJ means that gas is equivalent to electric heat at 12c/kWh. Heat pump multiplies that by roughly 4x, so 48c/kWh is the Breakeven point for a heat pump vs gas heating.

Heat is heat, it makes no difference. insulation would save you money on all heat sources though, and can be a pretty cheap upgrade (insulating the roof space, for example).

They give that advice because 'experts' (you probably mean salespersons) have to simplify a somewhat complicated story in a single recommendation for their market.

We can assume that you currently have a high power (e.g. 28kW+) gas heater and radiators that can only emit that kind of power at high water temperatures. This system works in tandem (place where has is burnt and devices that emit the heat throughout the house). A leaky house typically needs a higher heating power in the interest of comfort: it'll have a higher power loss, and you'll want to not spend days bringing it up to room temperature in case the power was out or what not. These heating systems are usually overdimensioned, so any variability in the power loss of the house is compensated for by simply upping the power output.

A heatpump is lower power, and therefore slower, and therefore you'll want to limit the heat loss of the house, because when things go wrong (somebody left a window open in winter), you're gonna have to wait some time before the pump's caught up. Calculating a building specific optimal heat pump power is already trickier, and it's trickyness is increased without that insulation.

Which doesn't meant that you cannot do it yourself! You can simply accept that response times are going to be slower (so, if you flip the temp up from 17C to 20C that it's gonna take half a day). Best is to just set it to a temp and leave it there, it's no longer the advantage it was to modulate.

Most important is to not underdimension the heat pump. I've never seen a salesperson offer it, but there's online communities of people who can and do calculate it for older houses (gas consumption is a good proxy). One thing to understand is that heat generator power (be it a heat pump, gas heater, whatever) needs to match the heat emission power of the system that releases the heat (radiators and floor heating most likely). The water is gonna run at lower temps with a heat pump, so that means that your radiators will emit less heat, and probably not enough. You need to make sure that at the water temp the pump outputs economically the power output of the delivery system matches. This usually means putting in floor heating and/or significantly larger and more efficient radiators.

Without fixing leaks and insulation, you've done the tech equivalent of throwing large amounts of resources at the problem rather than fixing the root cause :) Your CO footprint will be far better if you decided to fix the leaks & insulation.

This is a pretty broad topic, and you can watch videos from this channel to learn more: https://www.youtube.com/watch?v=dReyrSGokEQ

There are options to do a full passive house retrofit, or just add exterior insulation if you have the funds and inclination. Plus you can get better air quality with filtered air, lower mold/pollen issues, lower noise if you care about that and overall home comfort.

https://www.buildwithrise.com/stories/passive-house-retrofit...

Sure they can, you can absolutely use heat pumps to brute force it, been there done that.

Not only that, but since a heat pump is at least 3x as energy efficient as the most efficient gas furnace, using one results in about 1/2 the E2E CO2 emissions as the gas furnace when the grid electricity being consumed is natural gas based. If you live in an area with abundant zero emissions electricity, then you are heating without any C02 emissions at all.

That said, we should do both heat pumps and insulate better.

Your numbers are off. Thermal power plants typically do have a thermal-to-electric efficiency of around 30% (40% max), so with your heatpump having an electric-to-thermal efficiency of an assumed 300%, you end up with basically no difference in CO₂ emissions.

Note that there are some misleading efficiency claims for gas plants around 60%, but those are not for thermal-to-electric efficiency but for generating electricity plus district heating from waste heat.

60% would be terrible thermodynamic efficiency for a cogeneration plant. Modern CCGT systems crack 60% thermodynamic efficiency for just the electricity generation. With cogeneration, system efficiencies are typically in the 70-80% range.

60% is feasible for e.g. nuclear and gas, if you use more than one turbine and there is a big constant temperature differential. This typically isn't the case for gas plants which are intentionally variable and often intended to be cheap to build. While at peak temperature, they might run at peak efficiency around the theoretical maximum of 60% (thermal to electric) with a multi-turbine assembly, typically efficiency is far lower because gas plants usually don't run at peak efficiency and only have one turbine.

I don't think that any nuclear reactor has achieved 60% thermal-to-electricity efficiency. In a water cooled reactor the hot side starts with cooler steam than a combustion-fired plant can generate so it's hard to reach really high efficiency. Reactors cooled with helium, molten salts, or liquid metal could theoretically do better but I don't think that any actually-built power reactors have reached 60%.

The brand new EPR achieves only 37% thermal efficiency and that is considered a good number for a power reactor:

https://www.world-nuclear.org/information-library/nuclear-fu...

No, you are right, 60% is a theoretical maximum achievable maybe with supercritical reactor coolant. The actual maximum for existing reactors is somewhere just below 40%.

Modern combined cycle gas turbines offer thermal-to-electric efficiency over 60% (on a lower heating value fuel basis) at full design load, e.g. this General Electric system at 64%:

https://www.ge.com/news/press-releases/ha-technology-now-ava...

Approximating natural gas as 100% methane, that means the thermal-to-electric efficiency on a higher heating value basis is more like 57-58%:

https://en.wikipedia.org/wiki/Heat_of_combustion#Heat_of_com...

Neither of these efficiency measures include district heating with waste heat.

Keep in mind that pure gas heating is also not 100% efficient because you need to remove the exhaust, meaning you need to use a heat exchanger and no heat exchanger is 100% efficient either. Some of the heat gets carried outside.

Sure but these days even the cheap stuff is around 95% efficient because that enables the use of cheaper plastic exhaust pipes instead of insulated metal.

And it's irrelevant. Everyone is like "but if you have better insulation..." well golly gee, guess I'll get right on that. Tearing out all my drywall? Re-sarking my roof? Cost-free! Definitely not hugely disruptive, invasive and expensive activities which stand a good chance of forcing me to move out of my house while the work is complete...

People love throwing in about how effective insulation is, completely ignoring the vast difference in difficulty and cost it actually represents.

Never mind that you really, really can't do anything about that if you're renting.

I wouldn't say irrelevant but definitely nuanced.

Putting more insulation in the attic does not mean redoing the roof. Depending on what you have it might just be blowing in some insulation or adding matting. Of course there are options like spray foaming but it's not the only one.

You are of course right that if your walls are completely uninsulated you will probably want to rip out that dry wall and that will cost you. Maybe blown insulation is an option too depending on your specifics.

Do some math and see if it makes sense to do it if you don't want to do it purely for the sake of the planet. Drywalling isn't that big of a deal actually. The worst would be the ceiling and you don't have to touch that. Regular drywall on a wall is easily done solo by a home owner. Been there, done that.

It's funny what money makes you do. I had a choice to pay tens of thousands to have professionals do it or pay hundreds for materials and do it myself. I did lots of TIL and I have beautiful white walls again.

There are other advantages to fixing leaks & insulation such as controlling humidity/moisture, lowering mold/pollen/dust, lower noise, adding better air filtration, maybe even better fire protection. By "lower" I mean you can eliminate some of these issues. Not to mention a far lower energy bill. I would not describe these as irrelevant to most people.

Depending on the house, location and condition, adding exterior or interior insulation and/or aero barrier, or spray foam could be more cost effective and not so invasive as you think.

https://www.youtube.com/watch?v=_nOI99ew5MM https://www.youtube.com/watch?v=eYjF1afRqvE

It's actually exactly the reverse: for a house that's well-insulated, it barely matters how efficient your heating and cooling appliances are, especially if you're considering replacement of working systems.

The worst is when you rent. I live in an area that doesn't really expect much cold or heat. All the windows are single paned. The sun beating on the roof raises the top floor to the outside temperature plus 5 degrees. I can't fix any of it because I'm only here for a few years.

This is something to consider for a future rental property.

Some jurisdictions will actually basically pay the landlord to improve those things, worth checking community block grants and other similar search terms for your location.

Renting is a pain for heat pumps too, why would a landlord spend extra on one when they can pass the cost of utilities on to the tenant?

It's kind of nice in cool climates. I've rented places where I never had to turn on the heat once all winter thanks to all the heat coming up from lower floors. Temps were almost always above 60F and usually above 65 which is perfectly fine for cozy sweaters and blankets.

You’re describing my situation. How do you de-leakify a house?

- spray foam around/behind outlets on exterior walls (major leak point) which can be done often by just removing the outlet covers

- spray foam around windows (requires removing trim)

- caulk joints/spray foam rim joist in basement/crawl space

- spray foam around any attic can lights/duct work

- make sure ducts and air returns are sealed properly

Some home energy companies will do a free audit, in my case it's Mass Save. My in-laws on a limited income even got new windows and insulation for free.

AeroBarrier does the spray insulation strategy all at once for a whole home. Could look into something like that.

> You’re describing my situation. How do you de-leakify a house?

Do a blower door test and see where the air is coming in/out:

* https://www.energy.gov/energysaver/blower-door-tests

* https://www.youtube.com/watch?v=msZ_E-4GFs8

* https://www.youtube.com/watch?v=Q5vHxgq7GKo

Then plug the holes.

I would start by blowing insulation into the exterior walls (assuming they don’t have any), and insulating the attic. Also, upgrade the windows to double paned or better.

Fixing unintended holes in exterior walls is probably also reasonably safe.

However, randomly plugging intended leaks without understanding how the house is supposed to breathe can lead to condensation issues (mold and rot), carbon monoxide poisoning (if you have natural gas) and radon poisoning (if that is a thing where you live).

If you want to do more than I mentioned above, consider hiring an architect, or reading up on house ventilation designs.

The easiest is honestly to remove the siding and roof, and wrap the entire building in insulation.

Aero barrier and/or spray foam for an existing home should work well. But they are not long lasting and are often not environmentally friendly. You can also look into exterior insulation.

If possible and if you have the funds, try to do a retrofit: https://ekobuilt.com/2019/04/24/retrofitting-an-older-home-t...

https://www.buildwithrise.com/stories/passive-house-retrofit...

You don't have to do all the the things to improve performance -- you can pick and choose.

Insulation also matters for keeping your house cool and improving AC efficiency.

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