Been wondering about the right course of action for home heating.

Background is living in a 1920s house - detached, semi-rural position, mostly solid brick walls; double glazed and some loft insulation; suspended timber ground floors. So far, bills for our gas CH/gas cooking/gas DHW are still not horrendous. Two advantages we have are south facing main windows, so a lot of solar gain; and one small woodstove, costing nothing to run (as we have a firewood source, coppiced and processed ourselves, seasoned when cut, stored for minimum 2 years under cover and well ventilated).

We have so far resisted going for expensive EWI and floor insulation. Partly because this would be very difficult and disruptive (and would cover up period features), and partly because we may be moving anyway; and the trend locally is for developers to demolish and rebuild (or gut and massively extend) many older houses that come on the market. So any retrofit insulating we did might have a very short life.

All that said, our gas boiler is over 15 years old and the decision is either (1) replace like with like; or (2) spend more on a heat pump. The latter would be doing the "right" thing - by current national advice - but is it?

On (2) all the usual advice says no - not worth doing unless the house is super-insulated as well.

Am wondering, however. In our situation, might it be worth considering an ASHP that would be considered undersized; keeping the existing radiators; and topping up heat in cold weather by plug in convector heaters? An expensive option, but would it remain so?

In the UK, conventional wisdom (at least, in the chattering classes) suffers from a deeply ingrained belief (dating from the 1950s) that gas heating is cheap, electric is expensive. I wonder though if this will soon be all wrong? Solar and wind power costs are tumbling but electricity seems likely to stay expensive due to the high costs of maintaining back-up generation (or energy storage) for periods of low generaion by renewable sources. On the other hand, the costs of fossil fuel power (or natural gas replacement by hydrogen) may get even more expensive. (For climate reasons they certainly ought to be).

Alongside all that, construction materials- and wage- inflation is simultaneously making effective insulation much more expensive.

So in future, might it become a valid strategy to leave some older, period houses poorly insulated, use a smallish ASHP for background heat, and bite the bullet of topping up with old-tech plug in heaters to heat key rooms on cold days?

Obviously not the ideal solution from a climate perspective - but in the (post mid-century) future we may have surpluses of renewable electricity, with significant consequences for relative prices.

Also consider your DHW situation. Tank or Combi currently? If tank, what sort?

If you feel the cost of insulation is wasted effort, I'd suggest a HP is more so.

Posted By: PeterWatvalid strategy to leave some older, period houses poorly insulated, use a smallish ASHP for background heat

But could you resist turning the HP's flow temp up, make the rads run hotter than tepid? If you do, CoP plummets.

If youre thinking of moving and the house is likely to get trashed, then anything you do will in the main end up in a skip and be totally wasted. Unless you want to salvage bits out of the house at the time of sale doing nothing is likely the most cost effective and environmentally least damaging way forward.

Draughtproofing is a must then air sealing especially with cavirt walls. Both reduce energy use at low cost compared to EWI

Loft insulation 400mm+

I live without a formal heating system, bit of extra heat used during cold snaps.

Yes, in theory (Carnot heat engines) HT should be less good than LT.

But weather compensation meant that the HT were actually running as LT much of the time.

Also, the variation in SCoP caused by installation variation is large enough to make the HT/LT in-use CoP barely significant. This variation needs fixing.

Rgds

Damon

Very interesting, both of you.

Posted By: WillInAberdeendraughts hunted and stopped

To the extent that it might be called 'airtight'? In which case the phrase 'ventilate right' might apply?

I’m currently looking at a project where a sort-of similar question applies.

Old house, ground floor straight onto the ground. There will be some extensions which can be insulated properly (including the floors) and we will do a mixture of internal and external insulation to get the envelope of the old house reasonably well insulated.

At the moment it has a gas boiler & conventional radiators. The boiler is relatively new and has enough capacity that we could add radiators in the space in the extensions into the system.

So that would be the easiest option: keep the gas boiler and add a couple of radiators.

But would we be missing the opportunity - while doing major renovations - to future-proof the heating system? Of course none of us really know what will happen over the next 10-20 years. Maybe the price of electricity relative to gas will drop. Maybe heat pumps will become quieter and smaller. Maybe the gas system will transition to Hydrogen (seems a bit of a long shot). Maybe the return on investment on solar panels will improve.

We could stick with the gas boiler for now, and say that maybe in the future (when it next needs replacing, say) we could review the option of replacing it with a heat pump based system. The radiators would continue in use, it would just be the boiler that would get swapped out. Is that basically feasible?

Finding a location for an air source heat pump would be tricky (very tight urban site). Should we be looking into ground source heat pumps, seeing as the right time to put one in would be when the site is getting dug up anyway? But then that implies ditching the gas boiler at this stage.

Putting off a decision about solar panels seems easier - because it is moderately independent of the exact nature of the heating system. As long as the heating continues on gas, solar panels would be of minimal benefit. Adding solar panels could be considered if and when a transition to electric heating was being considered.

There’s also the question of whether or not to use underfloor heating in the extensions (it’s not viable in the main house, due to the amount of digging out that would be required). Potentially it could be a wet system that would run off the boiler, along with the radiators (although I need to check out the technicalities of that). And if the boiler were switched for a heat pump in the future, the underfloor heating could continue to work. But if there was a future switch to solar panels would that be an inefficient way to do it, with electricity heating up water for underfloor pipes when it could just directly heat up a dry system instead?

Lots of slightly vague questions. It feels very hard to make the right decision with so many unknown variables.

Posted By: djh

Posted By: lineweightPutting off a decision about solar panels seems easier - because it is moderately independent of the exact nature of the heating system. As long as the heating continues on gas, solar panels would be of minimal benefit. Adding solar panels could be considered if and when a transition to electric heating was being considered.

Solar panels and space heating are mutually orthogonal. There's minimum output from solar panels at the time you need space heating, so it's simplest to assume there's no interaction, and it's not far wrong as assumptions go. You can balance your winter electrical heating with solar panels on an annual basis, but you can do it equally with part-ownership of a wind turbine and the generation pattern for that much more nearly matches the heating season.

Things might be different 10+ years hence, though. For example battery storage technology might develop - whether that's at an individual dwelling level, or supply grid level with in/out tarrifs to match.

Posted By: lineweightBut would we be missing the opportunity - while doing major renovations - to future-proof the heating system? ...The radiators would continue in use, it would just be the boiler that would get swapped out. Is that basically feasible? ...There’s also the question of whether or not to use underfloor heating in the extensions (it’s not viable in the main house, due to the amount of digging out that would be required).

The best way of future proofing the heating system would be to put wet underfloor heating everywhere you can. That provides low-temperature heat that can be provided from any current or future fuel source. As well as providing more even temperature gradients within the rooms and more free wall space.

Posted By: djhAnything could happen, of course, but then again it might not ... Any possible developments more than ten years out aren't worth taking much account of IMHO

Fair enough, but though

Posted By: djhNothing's going to change the fundamentals of how much energy comes to the surface from the sun in winter

is true, the fundamentals of how much space heating a building will demand may (10yrs out) change relative to how much solar electricity is commonly available to each building on a current basis even during poor winter insolation. Demand may fall drastically while collection are and/or efficiency may rise drastically. That is the current trajectory, which exists despite current turmoil and conflict of interest, so it does seem a fair bet for 10yrs on.

Was the topping up comment not in reference to a building that requires no heating most of the year and as such the capital cost of an ashp makes it more expensive than direct heating for the little thats required each year. Or have i misunderstood somewhere?