lpm wrote: ↑
Wed Mar 29, 2023 9:53 am
I bet some of our ancestors were saying "Hypocausts? Do you realise how much they cost to install?"
The average UK house price is £294,000. £8k install cost is 2.7% of that.
Only the super-rich had hypocausts. The 99% from the stone age to the industrial revolution spent about 70% of their income on food, and that food was mostly just bread, because a lot else was unaffordable to them. There's some interesting info on Roman Britain period prices and wages in the St Albans/Verulamium museum. I found it rather shocking.
GCH was not some requirement you had to do. It was done because it was attractive to people. Incomes rose rapidly after WW2, people eventually got a lot better off and wanted to be warm. 1950s cold housing was no longer acceptable, even in the social renting sector. GCH was much the most economic way of heating houses where there was piped gas. Like lighting with the invention of light bulbs and electricity, which made good lighting a mass application rather than a privilege of the rich, so GCH turned being warm from a privilege of the rich to a mass application. Though in the lower cost housing sector, you'll find plenty of cases where cheapskate developers put storage heaters in, because they didn't care about their tenants' running costs. My sister lives in such a building. Even today.
£8k is what it costs to install an actual heat pump, assuming that the house is suitably insulated and the radiator plumbing is suitable. That's the best case scenario. People with the best case scenario are easier to persuade to do it.
The problem is that a huge amount of the housing stock is not like that. Take my house, frinstance. Built in 1938 with solid walls. When I bought it in 2000, the walls were so cold, that condensation routinely formed on some of the walls, especially inside or behind cupboards, leading to extensive wet rot in the floorboards. I had to replace the floorboards, and solve the cause of the problem. Fortunately, having a smaller number of larger rooms than many similarly sized properties, it was feasible for me to dryline the walls on the inside with 50mm insulation, cover with plasterboard, redecorate. External cladding was not practical due to insufficient roof overhang. Most British houses have insufficient roof overhang. That action alone cost more than £8k in 2000 - given that it necessarily included redecorating every external wall. Of course I had to pay much else, the woodwork replacement, and woodworm and rot treatments. I had a new roof put on in 2007 as part of a roof conversion, and that is insulated to 2007 standards, an action which also cost more than £8k in 2007. (I now don't have a loft.) The house became warmer with that better roof, but still isn't sufficiently insulated for heat pump heating. I was able to do a back-of-the-envelope and I reckon I'm about D to E on the efficiency scale, which isn't good enough for a heat pump. Short of knocking it down and starting again, it's quite difficult to work out what would be good enough and not end up costing a real fortune. At some point when the house needs a redecorate, maybe we rip off the old insulation/plasterboard and try again with modern materials/methods. Maybe we go for 100mm. There are some locations where that will be difficult, like in the bathroom where the shower and toilet are installed against exterior walls, behind where kitchen cabinets and sink are installed against exterior walls.
Heat pumps work best with underfloor heating. Retrofitting underfloor heating is a project in itself, excluding the heat pump, of considerably more than £8k in most houses. Maybe my house wouldn't be good enough without further installing underfloor heating. The back half of the house has concrete flooring. The kitchen-diner concrete floor is tiled with high quality floor tiles I assumed would last my life.
The average age of the housing stock in Britain is about 65 years or something. Many houses are small, have small rooms, and what I did in terms of dry-lining is difficult for them, and in my case wasn't even enough.
"Heat pumps is easy" is, I'm sorry, cloudcuckooland. They are only easy in ideal cases, which is only a minority of real cases.
There are various serious reports available on these issues, looking at the distribution of houses and likely costs for different situations. I have cited references to them in the past on this forum, so I won't repeat them. IIRc, a few years a common conclusion was that the average installation cost, including associated works to make it acceptable, would be something like £25k. That covers cases where you only have to spend £8k, and many other cases where you have to spend a lot more than £25k. And that is not the cost of doing it today, rather that is a predicted future cost when there are lots of installers well experienced in doing the work, it would be routine work not a special, and the materials would be mass produced. And then there's all the people who live in apartment blocks, where you need an overall solution for the block, not a flat-by-flat approach.