Considering hybrid Air-to-Air and GCH

chillee

Hi all, here's the context of our situation. We're a family of 4 (2 adults, 2 school-age children) living in a 1970s-built detached house. Our heating is provided by a decade-old, gas-fired boiler which is only plumbed into the central heating radiators. For hot water, we have a 210L, vented, directly heated hot water cylinder which is not plumbed into the boiler and is only heated by an immersion heater. We have rainfall showers which are fed by the hot water cylinder.

With children, we do a lot of laundry and our eldest loves her long hot showers. As you can imagine, our electricity and water bills are quite high. Our average daily electricity usage between 20-30kWh and our monthly bill usually over £200 on a fixed tariff. We installed solar panels and 27kWh of battery storage in March 2025 and this has helped massively to bring our electricity costs down.

I've considered replacing our gas-fired boiler with an air-to-water heat pump, but the initial quotes I've had are higher than I'd like so I've been considering the possibility of keeping our has central heating as is and adding an air-to-air heat pump system to provide some more-efficient heating, but also cooling in the warmer months.

The summer cooling is very attractive, but also the possibility of saving on our gas bill. Granted, we would still be heating our water electrically, it wouldn't eliminate our gas bill and we wouldn't be eligible for the BUS grant, but I think we have sufficient spare battery capacity to make this a worthwhile step forward.

Does anybody have any experience taking this kind of hybrid approach?

FreeBear

Is the old boiler by any chance, a Baxi back boiler ?

If so, virtually nothing to go wrong, but it is getting difficult to find Gas Safe engineers conversant with servicing them - Had one [redacted] that claimed I was missing a grommet around a thermowell, and refused to accept one was never fitted (none listed on the spares sheet, or any other available documentation).

The old Baxi boilers (and anything else from that era) are grossly inefficient at around 65% if you are lucky. Compare that to a modern condensing boiler driving suitably sized radiators which would be 90% or more. Replaced my old Baxi with a new combi (also fitted larger radiators all round), and coupled with a smart control system, have managed to cut gas consumption from ~8000kWh to a little over 3000kWh per year. Some of that saving comes from replacing the windows & doors along with plugging some nasty cold draughts.

I had wanted to go for ASHP, but at the time, I would have been required to undertake thermal upgrades recommended on an EPC. Something that just wasn't in the budget. One year later, this requirement was dropped…

Personally, I'd recommend biting the bullet and getting rid of the old gas boiler and installing an ASHP. With the current inefficiencies, your return on investment won't take too long even if the initial up front cost is a bit on the high side. The alternative is to get a plumber to install a three way valve on the CH plumbing and use the gas boiler to heat the water tank (may need a new tank though).

chillee

The gas boiler is a Worcester Greenstar 30CDi. The previous owners of the property had seemingly never maintained it we discovered a well-established a water leak when we moved in. We've since had it repaired and it's been serviced every year since. One plumber said we should think about replacing it sooner, but the next plumber said he had the same boiler at home and ours was still going strong. 🤷

We would need a new hot water cylinder and I'm not sure how well it would even fit in the airing cupboard where it's currently located. We don't have a garage or anywhere else we could put a large water cylinder. So, that's another consideration.

I probably should pay for a proper consultation and quote on an air-to-water system before dismissing the idea, but I still like the idea of cooling in the summer…

FreeBear

The gas boiler is a Worcester Greenstar 30CDi

OK. A fairly modern condensing boiler with an efficiency of around 89%. A fairly solid model, so if it is still working, not much point in replacing it. With a peak output of 30kW (way more than many houses really need), you have plenty of capacity for a fast reheat of a water tank. Really surprised that it wasn't plumbed in to provide hot water. Would have saved the previous owner and you quite a bit of money over the years.

If you did go for a hybrid system, you wouldn't qualify for the £7500 government grant. So do bear that in mind when doing any costings.

Newbie_John

27kWh battery and Flexible tarrif? You should really get cheapest rate out there - Go etc. that would instantly cut your electricity cost by 50%.

If you switch to some cheap <10p rate tarrif then yes, it would make a lot of sense what you suggest.

Otherwise you need to calculate it all yourself, keeping gas costs up to £200 in standing charges a year, heating water electrically should be free for you because of solar with exception of winter - but again ToU tarriffs come handy.

chillee

https://forums.moneysavingexpert.com/discussion/comment/81985923#Comment_81985923

We were also surprised about the hot water configuration having come from a combi boiler in our previous house. Even more so when the electricity bills came in!

I did ask a plumber - who was doing another job for us - how much it might cost to plumb in the hot water cylinder and without providing an exact figure he suggested it would be a few thousand pounds. We'd need a new tank as the current one doesn't have the heating coils inside in.

chillee

https://forums.moneysavingexpert.com/discussion/comment/81986017#Comment_81986017

We're currently on Good Energy's EV tariff. We don't yet have an EV, but the tariff didn't require one at the time we signed up. Unfortunately, it does now so we'll need to review the situation by the time it comes to contract end. We're currently considering getting an EV over the summer so that should keep our options open.

But, yes, having the ability to store a day's worth of electricity in our batteries and the 6.6p/kWh overnight EV rate has made a massive difference to our bill. If our eldest has a shower then we usually need to run the immersion for 2-3 hours to get enough hot water for the rest of us so that's an easy 6-9kWh used during typical peak times. So heating water is still a large electrical demand in our household. This is why I'm so torn with all of the available options and it gives me a headache just thinking about it. I've also seen heat pump hot water cylinders as yet another option…

Newbie_John

Ok, that changes everything. You probably use up to 10kWh for heating water a day, 3600 a year - so about £250/year with your current electric set up, or up to £500 if your cheap rate doubles.

We have A2A for heating house and solar thermal for water - although as there are no grants for it anymore it doesn't seem like viable option.

Are you able to export all your solar electricity? If not you can use it for heating water?

I think you'll need to do maths yourself using your current usage - with electricity rate of around 10p - heating with heat pump will halve your heating costs and it will cost you a quarter of current hotel water tank, also getting rid of gas standing charges.

A2W sounds like a complete solution for you. One tool for all your needs. A2A may be great if the price you pay after grants is very low and you would just need to accept your immersion heater costs as they are.

chillee

https://forums.moneysavingexpert.com/discussion/comment/81986154#Comment_81986154

Including the outlier days, we averaged around 30kWh of daily household demand in April. With the 27kWh of battery charged up each night, we've been able to export most of our solar apart from a few days when it was particularly cloudy. In April, our average daily generation was 18kWh.

The immersion is on during the overnight cheap window so we always have a full tank of hot water in the morning. There's then a 1-hour period early afternoon and 2 hours in the evening to top up the hot water. If all 4 of us decide we want a shower on the same day then we may need another couple of hours of the immersion.

A2W does indeed seem like it would cover all of our needs apart from cooling, but it's also the largest upfront cost. Going by the Heat Geek online estimate and including the additional plumbing, we could be looking at £7k+ with the BUS grant.

I've not got a comparable A2A quote as I'm uncertain what type of set-up would be best suited. Ideally, we'd have warming/cooling coverage in all 4 upstairs bedrooms (I think with ducted ceiling vents), the lounge and kitchen diner downstairs could have individual units. It's something I need to do more research on.

zxzxzx

I have gone from oil to lpg to lpg plus A2A to A2W plus A2A. With solar and battery.

In your position I would get multiple A2W quotes, particularly Octopus who installed mine as they seem to be driving this tech to user benefit.

Solar, batteries and HP is the perfect combo.

Heat pump efficiency will kill immersion costs for hot water. (3-5 COP)

When that is done add an A2A in your lounge (mine cost £1500) and/or diner for shoulder months warming and summer cooling, does the rest of your house really need cooling?

Just my thoughts FWIW.

michaels

Will you really get a 3 to 5 cop for heat pump hot water heating? Flow temp has to be high for this application.

Loathe to say so but would a combi boiler not be the answer for the hot water?

However adding A2A might help reduce bills especially if AC was also really needed.

Are there any ballpark costs for A2A installs of up to say 5 rooms?