SteamyTea

You could dedicate part of your PV to DHW. That could reduce the need to limit exports. You should be able to work out, for your orientation (that's panels, not long girly showers) and location the best proportions to get you maximum efficiency.

Go for it, then you will wish you kept your old boiler. Do a bit of general research on ASHPs. Like all internet research, generally, the negatives reports outweigh the positives, but that is because people are often idiots and don't do research. Here is a good example of what can happen when no proper advice is sort first (you can skip a few of the early pages).

Have a word with @canalsiderenovation He can tell you who to avoid.

It will get recycled though, do lowers the embodied energy of the next product it gets turned into. It must hurt when you fill it up.

Just a thought. How bad is your old oil burner. Would spending part of that 3k on improving the house, better heating controls, and more than just a service on the boiler be money better spent? An example is my neighbours. They get new cars every 3 years, 'because they need reliability'. We live on a good (for Cornwall) bus route, the two schools are within walking distance, 3 supermarkets less than half a mile away, A DIY shed, MacDs, Dominoes, and Costa close by. Probably costs them 8k a year in depreciation, and he whines that it costs nearly 100 quid a month to run the house.

Blackthorn and gorse. Grows like weeds down on the Cornish North Coast.

Global sustained economic growth has always happened during times of low, and stable, oil prices. It is then down to governments and consumers, to decide what we burn it for. Do we just add it into inefficient vehicles, or build some wind turbines. Heat thermally leaky housing, or make cheaper insulation and windows. Seems to me we just like to burn it, thus keeping old infrastructure going. You are in a position to choose. Choose wisely.

A decade ago, Mike L, over at the other place was whining to me that he fitted s GSHP just as the oil price plummeted. Been low ever since. All that fuss in 2006/7 that oil would hit $250/barrell. Even the greens new it would not happen.

Green and Eco are nonsense terms, they have no numbers attached to them. Oil burners, like gas, are not dreadful on emissions, so look into replacements. ASHP may well be worthwhile, depends how easy your current pipework can be modified for different controls and lower temperatures. RHI is a costly route to go down. Spend an hour on eBay and see what is kicking about. If you want to reduce CO2, look at your car. Makes me giggle when people on here talk about low energy housing and then drive a Landrover, Ranger over, large Merc or Audi. This is just pottering around.

One advantage of gutting a place is that you can deal, relatively easily, with airtightness issues. Just make up your own blower and start sealing all the leaks.

Stick to building regs https://www.planningportal.co.uk/info/200135/approved_documents

No, but I do live on my own, but 5 adults in neighbours house and they seem clean and tidy. If I needed more hot water, I could fit a larger cylinder, cheaper than a new boiler. Read my rely about the flow rate, it is enough to run two showers as it is, easy to fit another pump to run more, but I would be running out rooms to fit showers into. How well does a combi boiler work in a power cut. At least I have some stored hot water, definitely good for 2 days, probably 3. The flow rate of most, cheap, combi boilers is pretty pitiful. Had one in my old house and it took 15 minutes to fill the bath. This is pretty pointless really, you do not understand, and cannot be bothered to learn the differences in the technology, you just have a very backwards view on heat pumps. You assume they are low powered, only low temperature, are super expensive to buy and install, while any gas combi boiler has infinite capabilities, gives 100% reliable service, costs the same as a week in a Travel Lodge (do they use combi boilers in hotels?) and produce less pollution. I am not going to change your mind, but I will pick you up every time you say 'they don't work' or similar, as that is just nonsense, and I have no tolerance of people that talk nonsense.

200lt in this house. I can also get a flow rate of 20lt/min if I want. (I don't have an ASHP but the arithmetic is the same)

Limitless, like it never, ever runs out?

I could have had mains gas fitted back in 2005, was going to be £20k. Divide that by 16 years, £1250/year. So that is 3 times more than what I currently pay in electricity. Not only do I get plentiful hot water, I get lighting, cooking, radio, clothes washing, IT services. I wonder why we don't have gas lights any more, they should be the cheapest form of lighting.

So half way there then. I was answering you uneducated assertion that a heat pump can only supply 5 minutes of hot water. Go and read all 3 pages of the thread and see what it is about before spouting your usual nonsense about heat pumps.

I am saying that they can supply as much domestic hot water as you want. You name the quantity, I hall find a solution for you.

That is the only true statement in your reply. It is thermodynamics. Show me the data that they cost 10k and only supply 5 minutes of hot water? Or stop talking nonsense.

Do they have lower CO2 emissions? Should they have an annual service? If they are in a rental, do they need a safety certificate? Can they be easily installed by a 'normal' home owner that can do DIY? Do they need a dedicated supply and meter if one is not already installed? How do you proportion the meter rental? And the big one, if no mains gas is available, are they still suitable? You really do not like heat pumps do you.

Yes, you get 'clumping'. Stratification does not really happen, more a case of a spatial-temporal changing temperature gradient. There is probably good reasons they are not common.

Am I right in thinking that while oil boilers can condense, they do not modulate their power?

That is because of the relatively small external wall area as a ratio to to the whole area. Changing the floor U-Value, when using UFH can have a much larger impact, the delta T is so much greater.

I have had a few jobs queried because of this. Charge one price to put a hole in, and another, sometimes higher, some times lower, to not put a hole.

May have come from comparing heating degree days distributions. If I look at a 2°C difference in my HDDs, I get a 20% difference. Not surprising as the weather is very variable on the coast.

Not gone though the whole list, but I don't think the specs are hitting the current standards. If that is the case, then sack your architect.