@toodles - as you may recall, I have a listed (Grade II) building, and so have some experience in this area. It doesn't have to be expensive, that isn't necessarily the bar, it is often more about aesthetics (the building is after all listed for a reason) and practicalities, which often boils down to space in small listed buildings. In my own case, from the top down:

Loft insulation: no problem, same cost per square meter as anyone else  

Walls: major problem, and they are also a major source of heat loss. External cladding would destroy the building's character, internal cladding will reduce already limited interior space, affect the aesthetics, and often the walls aren't straight rectangles meaning lots of work and cost  

Windows: secondary glazing is doable, doesn't fall foul of listing, is not expensive especially if DIY (I use PET-G sheets held in place with magnetic strips) and is surprisingly effective (I forget the U values, but they are far closer to double glazing than single glazing). It is also a very effective way of dealing with draughts from poorly fitting windows, a major cause of heat loss in my home, eg I have some cast iron casements in ye olde oake frames that have huge gaps, the secondary glazing effectively seals them

External doors: make sure they fit and have weather seals, add heavy curtains if you like

Fireplaces: seal the flue, various devices available to do this. Make sure you remove whatever it is before you light the fire!

Floors: I have solid ground floor floors and limited ceiling height, not really practical to add any insulation

Those of us who choose to live in a listed building know there will be costs as well as rewards, and higher heating bills are often one such cost.

It's worth also mentioning that if you choose to install a heat pump, being listed will also trigger a need for listed building consent and planning permission, no permitted development here. The planners should look favourably on such proposals, you are after all trying to go green, but they are a vicarious bunch and can come up with all sorts of objections. Mine tried the bat trick, until I pointed out their secret bat map was based on whatiffery, and bore no relation to reality. I can confidently confirm no bats were harmed during the installation of my heat pump. 

I don't think it's a controversial topic at all, @toodles, but I also think the answer is no.

From all that I understand about listed buildings, it's not the listing that's the problem; it's the design of the building given most listed buildings are older properties. Older houses were designed to breathe whereas modern insulation is trying to reduce air flow and therefore warm air loss, so very often attempts to insulate are also attempts to get a building operating contrary to how they were designed. Relaxing grading requirements would make it easier and therefore cheaper to apply inappropriate insulation methods to a building and therefore introduce problems that could damage both the building and the occupants.

On the other hand, there are a lot of products on the market that are specifically designed to insulate older houses in ways that work with rather than against the building. These products and the techniques involved in using them are not necessarily well understood by the average builder, but specialists can work wonders. Nonetheless, a 17th century farmhouse is never going to be as thermally efficient as a modern design of house so the higher cost of the specialist insulation products and the lower return on the result mean an old property is always going to be more costly to heat and a prospective buyer has to factor that in before they decide to buy. Changing the grading status requirements won't change that IMHO.

@cathoderay Thank you for that clarification; any bats would probably appreciate the low level gentle heating anyway - but I’m not sure you would have appreciated their guano! Toodles.

@toodles - perhaps more likely cool chilled out bats, the heat pump after all puts out cool air. But good to be free of bat poo.

@majordennisbloodnok - good point which I didn't mention, there are technical obstacles too that arise not from the listing, but the fabric. 

More generally, I go back to the point about listing is done for a reason, to protect the character of what are often very attractive, if nonetheless not very thermally efficient, buildings. It is a case of you can't have your cake and eat it, if you live in a listed building, you accept there will be extra costs, the one thing you can't do in my opinion is turn the building into a passivhaus monstrosity that is as green as it gets, yet has lost all its character.  

Posted by: @cathoderay

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@toodles - perhaps more likely cool chilled out bats, the heat pump after all puts out cool air. But good to be free of bat poo.

@majordennisbloodnok - good point which I didn't mention, there are technical obstacles too that arise not from the listing, but the fabric. 

More generally, I go back to the point about listing is done for a reason, to protect the character of what are often very attractive, if nonetheless not very thermally efficient, buildings. It is a case of you can't have your cake and eat it, if you live in a listed building, you accept there will be extra costs, the one thing you can't do in my opinion is turn the building into a passivhaus monstrosity that is as green as it gets, yet has lost all its character.  

Actually, I quite like buildings like the PassivHaus designs but I do agree their character is utterly different from that of an old building. Nonetheless, the key point I think we're both making is worth underlining again and that is that historical and modern designs are fundamentally different technically as well as aesthetically and any attempt to treat one like the other will just not work. It's a bit like treating a Lamborghini like a Land Rover; you can do it but it'll break sooner or later and perform badly in the meantime.

Posted by: @majordennisbloodnok

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From all that I understand about listed buildings, it's not the listing that's the problem.

My in-laws live in a converted grade-listed property that has been turned into apartments. Unfortunately, they’re not allowed to make any changes to the windows. Some of these old metal frames are so warped that there are gaps nearly an inch wide, allowing significant amounts of cold air to enter their home. While they don’t mind much since they rely on a gas boiler, this would pose a serious problem with a low-temperature heat pump, especially considering how many windows like this they have.

Quite agree, @editor. As with most graded properties, the windows would have to remain unchanged.

That doesn't, however, stop your inlaws from investigating secondary glazing options which could well sort out the draughts. Nonetheless, once one goes down that route then all the issues of the building's breathability come into play which is, of course, the point I was making. If the rules related to listed buildings were relaxed it would make it easier to change the windows but whether the draughts are stopped by new windows or some form of secondary glazing the knock-on problems are about the same. I just don't think changes to the rules on graded properties would deliver the desired effect of reducing the cost of heating such houses.

Posted by: @editor

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Unfortunately, they’re not allowed to make any changes to the windows. Some of these old metal frames are so warped that there are gaps nearly an inch wide, allowing significant amounts of cold air to enter their home. While they don’t mind much since they rely on a gas boiler, this would pose a serious problem with a low-temperature heat pump, especially considering how many windows like this they have.

Hmm, the joys of old buildings! Are the metal frames mounted in wooden frames, as is often the case? If so, and enough exposed surface is available, then the magnetic strip, only 1/2" wide for up to ~1sq yd (Imperial for old buildings!), can go on the wooden frame. If the wood is also not level, get the chisel and fill fairy in at midnight... Another less satisfactory but possible option is to mount the magnetic strip on the wall, just outside the window reveal.

Draughts are a major problem, they can ramp up the air changes to alarming levels that then have a significant cooling effect. Putting aside the problems with heat loss calcs for a moment, compare these values for a sample room from an old (2021) Freedom Heat Pump Heat Loss Calculator, with just the air changes per hour altered: 

With only two air changes per hour, not at all inconceivable with major draughts, the air changes account for almost half of the room's heat loss.   

Posted by: @majordennisbloodnok

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That doesn't, however, stop your inlaws from investigating secondary glazing options which could well sort out the draughts. Nonetheless, once one goes down that route then all the issues of the building's breathability come into play which is, of course, the point I was making.

My reading of the rules is that secondary glazing is definitely OK in listed building. The only alteration is a removable magnetic strip, on a par with hanging a picture on a wall, which their Lords High Commissioners for Listed Buildings let us do. Certainly old buildings breathe and need to breathe, but then there is breathing vs forced air induction as in a winter gale blowing on a leaky window. I haven't noticed any problems in the rooms I have fitted with secondary glazing, while there is certainly one huge gain, little or no condensation, achieved partly because the of the secondary glazing itself and partly because the heating is mostly always on in winter. Not only does this little or no condensation improve comfort, it also helps prevent rot and decay in the window frame, and is a worthy gain in its own right. Furthermore, the house also breathes in other ways, the walls, the doors and the flues. I should also perhaps add that term 'breathability' is a bit misleading, it is not primarily about air movement, but rather water movement, and it could be argued (I'm putting this up as a point for debate) that the benefits from reducing condensation outweigh the loss of permeability (air movement).    

@majordennisbloodnok Just me but, I would much prefer to live in any PassivHaus than listed building, but, then I have particular need of good lighting, level floors, wider walkways and stairs etc. These days it is not just my poor sight but other bodily needs for comfort show a preference for the easier life too! Comfortingly, Toodles.