Hello

[Caerefail]

Hello, 

I've just joined as I've been reading the forum for a while and found it very useful. My next project could be an air source heat pump but I'm not sure yet as we have 12mm piping buried in the walls and I don't want to have to redo all the piping. House was built in 1992, with cavity wall insulation and the loft insulation has been topped up. 

Any comments and suggestions gratefully received. 

[Iceverge]

More info please for an informed decision. 

 

ASHP can be expenses if you don't have a suitable house. 

 

Do you know how much gas you use per year for instance as is?  Do you have any idea of the flow temperature of the water to the radiator's? 

[Caerefail]

Thanks for the reply. We are off grid for gas, heating is by an oil boiler, we use 2000 litres a year, averaged and rounded up. 

Output temperature from the boiler is 60 degrees C, return temperature is 45 degrees. 

The house is 201 square meters, according to the EPC. 

Hope this helps. 

Edited March 26, 2023 by Caerefail

[Iceverge]

Ok, useful info. 

 

At 60deg flow temp you're better off with the oil I think. 

 

2000l is about 17000kWh delivered heat to your house at a boiler efficiency of 85% and about £2000.

 

Something like a highly efficient split ASHP would only achieve a COP of about 2 at 60deg. 

 

 

At 17000kWh delivered heat you would need to buy in 8500kWh or electricity, at 30p/kWh you would pay £2550 per year for electricity with a heat pump that could cost £10k to install and have a lifespan of 7 years. 

 

£550 * 7 years and £10k up front you could end up at £14k out of pocket for the first 7 years and every 7 years after that. 

 

 

 

 

 

[Iceverge]

What is the motivation for switching to an ASHP? 

 

There's no benefit for cost. 

 

An air to air (A2A) may be different. 

 

A single unit will deliver heat at a COP of 5 and an installed cost of £1500. Lifespan 7 years. 

 

Say it does 5000kWh/heat/year so £1000 bought in at 30p is £300 per year. 

 

£300*7 +£1500 is £5000 for  25000 kWh of heat delivered of 5p/kWh. 

 

This compares to an ASHP in the above case of a 7 year cost of £10k plus £2550/year for 17000kwh X 5 or 32p/kWh of delivered heat. 

 

Or about 10.5p for the oil boiler. 

 

TLDR. 

 

Oil costs you 10.5p/kWh

ASHP would cost 32p/kWh

A2A could cost 5p/kWh to supplement the boiler. 

 

 

[Caerefail]

Many thanks for the replies. Plenty of food for thought. The motivation for considering ASHP is that our current oil boiler is 15 years old and will need replacing sooner or later but government plans are looking at banning the sale of oil boilers from 2026. So it's either replace in the next 18 months, go ASHP while there is a grant available or wait and see but probably have to go ASHP in the future anyway. 

[Iceverge]

58 minutes ago, Caerefail said:

The motivation for considering ASHP is that our current oil boiler is 15 years old and will need replacing sooner or later but government plans are looking at banning the sale of oil boilers from 2026.

 

I wouldn't hold my breath. Good governance comes from understanding  and this is a clear example of ignorance of the facts.  

 

I should happily continue with an oil boiler if I were you, wait until it goes kaput and replace with a new 90+% efficient model when the time comes. 

 

The ASHP grants just inflate the prices anyway so don't worry about that. 

 

Instead work on reducing your energy use. More insulation. Airtightness. Maybe some decentralised MVHR. 

 

Then consider PV and A2A. 

 

 

 

[markocosic]

TL;DR is too short @Iceverge

 

Agree throwing in an A2A unit for baseload heat to reduce oil use is something that ought to have been done years ago. 

 

 

That doesn't help you with hot water though.

 

And seasonal COP will not be as bad for the ASHP as it is at peak condition.

 

And you can drop the peak flow temperature (you'll have to) by narrowing the DeltaT - going form 60/45 to 55/50.

 

 

A system peaking at 55C will have a seasonal average COP of around 3.5; it'll do the hot water too; the heat will be distributed more evenly, and it'll last more like 15 years.

 

https://midsummerwholesale.co.uk/buy/samsung-heat-pumps/samsung-stealth-12-heat-pump

https://midsummerwholesale.co.uk/buy/vaillant-heat-pumps/vaillant-arotherm-plus-12kw

 

 

Run those figures against an A2A with immersion hot water - and factor in oil boiler and tank maintenance/replacement allowance - and I don't think it's as TL;DR clear cut.

 

A2A wins in the very short term. A2W has it's attractions in the longer term.

[SteamyTea]

18 hours ago, Iceverge said:

2000l is about 17000kWh delivered heat to your house at a boiler efficiency of 85% and about £2000.

An oil boiler is either on or off, an ASHP can run for prolonged periods of time.

So you may find that your current radiators can deliver the required energy needed, but at a lower flow temperature i.e. 45°C.

Just a case of working it out.

 

[Iceverge]

@markocosic  even at 15 years lifespan for an ASHP the cost is 16p/kWh. 

 

Agreed it's not the whole picture. 

 

It depends on a myriad of factors but I can't seem to make sense in many cases on cost alone. 

 

@Caerefail, what are your current electric rates? 

 

Do you have PV? 

 

Is it a combi oil boiler or do you have an existing UVC? If so what size?

 

 

[ProDave]

9 hours ago, Caerefail said:

Many thanks for the replies. Plenty of food for thought. The motivation for considering ASHP is that our current oil boiler is 15 years old and will need replacing sooner or later but government plans are looking at banning the sale of oil boilers from 2026.

Unless the water jacket of an oil boiler rusts through (I did have 1 replaced at less than 1 year old due to a manufacturing defect) they will go on forever.

 

The burner is a completely separate unit, very serviceable and replaceable if it really can't be serviced.  We had a rental house with a Grant outdoor combi boiler that was still working at 30 years old when we sold the house.  It might have been on the verge of needing a new complete burner.

 

If it really looks like spares are going to get hard to obtain, just buy a spare complete burner and put it into storage.

[Caerefail]

Current electric is 30.42p per kWh, fixed until next May. It's an EV tariff but we can't get a smart meter as no signal! We have a 7 kW PV system with 2 x 8.2 kW batteries. The oil boiler is just a standard condensing boiler. Hot water cylinder is standard unvented, mainly heated by solar diversion, sorry, no idea of size but not huge. 

[Furnace]

32 minutes ago, ProDave said:

they will go on forever.

My Trianco Redfyre is at least 35 yrs old and just keeps going. I have it serviced regularly (every 5yrs) and the chap always says it's fine. They don't make 'em like that no more. I'm praying it will survive until I move in a year or so.🙏

[markocosic]

19 hours ago, Iceverge said:

It depends on a myriad of factors but I can't seem to make sense in many cases on cost alone. 

 

If "displace some oil with cheaper lower co2 space heating" is the objective then A2A.

 

If "replace all oil use including winter dhw with lower co2 and fit a decently sized hot water cylinder/heat battery whilst at it" then A2W.

 

Once is a temporary cost reduction/co2 reduction exercise until the existing setup goes bang and you must replace. It makes use of the existing setup whilst there's life in it so that it needs to do less.

 

The other is what you'd replace it with; that also ensures more even heat distribution to the balance of the property and ditches the liability of oil tanks and associated crapsicles.

 

 

Say 15,000 kWh heat demand.

 

(I doubt it's as high as 2000 litres of oil at 80+% efficiency; boilers usually more pants than you think and controls usually more pants than you'd want)

 

COP 3.5

£0.30/kWh long term 

£1285/yr in leccy 

 

Some will usefully come from PV but let's ignore that.

 

£0.085/kWh marginal rate.

 

225000 kWh over 15 years adds about £0.005 per £1000 of capex.

 

£0.13-0.15/kWh all in is about right. COP dominates so worth spending on the hydronic installation to improve that. 4 with rads usually doable. 4.5+ difficult.

 

Possibly worth entertaining an A2A today that then gets supplemented by an undersized heat pump later, which can use existing rads to provide heat to hard to reach rooms (where a single minisplit can't distribute to) and a new cylinder to bring down install costs Vs swapping all rads.

 

Not disagreeing with your logic...I have a 15 year old combi and a A2A for similar cheapskate reasons...but the heat distribution does suck and the draughts do suck and two controls suck and it is noisy vs low temperature radiator based heating. But I'm cheap so have it. 😉

 

[Caerefail]

Thanks for the comments everyone. EPC reckons heating at 23000kWh per year!!! I suspect based on the oil consumption it is nearer 15500, especially as the 2000l is rounded up. 

I think I'll get some quotes and see what they say. I know cost wise it's likely we'll not do anything!! 

[Iceverge]

An accurate oil usage should be easy to obtain if you look back through receipts or bank statements. 

 

How big is the house?

 

Can you describe the current insulation, windows etc? A better result may be obtained from upgrading the fabric. 

 

I'm not massively aware of the situation in the UK but I see no reason why the ASHP grant would not be available to A2A. 

 

Given the amount of PV I think any heat pump for DHW will never ever be worthwhile.

 

Maybe a full multi-split A2A like @Hanksyand a few others.

 

 

[Caerefail]

On 26/03/2023 at 15:27, Caerefail said:

House was built in 1992, with cavity wall insulation and the loft insulation has been topped up. 

House is fully double glazed and is 201 square meters from the EPC. 

Average oil consumption over the last 10 years is 1889 litres, hence rounding to 2000.

But really, my main query was about the possibility of using existing rads and piping if we did look at ASHP. Thanks again for all the views. By the way, I don't think A2A is likely to be the way we go. The house is long and any A2A system would only be able to heat one room.