Heat Pump vs Gas Boiler: Lifecycle Cost Comparison (UK)

[JohnMo]

No they won't and I completely agree, it more like 95%+ of boilers operating at high flow temps.  There are lots of heat pumps badly installed also, running higher than ideal temps, with on/off controls and lots of zones.

 

But if we are comparing on a like basis, lets compare from a similar starting point, not apples against pears.

[Marvin]

11 hours ago, JamesPa said:

Yes, but the point is 3-4 times less carbon emissions, ie approx 3-4 times less fossil fuel used..  Furthermore as the grid decarbonises this can only get better. 

 

If you are looking for a completely fossil-fuel free solution you are currently out of luck, unless you have sufficient local generation capacity or local heat storage on an annual scale.  But a 3-4 fold reduction is an extremely good start and, with the promise of a greener grid, will get us to where we need to be.  Doing nothing on the grounds that there is no perfect solution will not.  

Adding to this is using power from PV installed on the same building. Something difficult to emulate using a gas boiler!

[Marvin]

2 hours ago, JohnMo said:

The only thing to say in defence of a gas boiler is the 80% efficiency, is not always the case. 

 

If you compare it on a like for like basis i.e. on low flow temperatures, a part load efficiency is being quoted for our boiler (Atag A325ECX) of 109.2%, with a flow temp of 36/30 return.  When looking at DHW with flue gas heat recovery it is being quoted as annually 95%.

I didn't know a boiler could be over 100% efficient. How does it produce more energy than the gas inputs? Is that because of the heat produced through the electrical componants?

[JohnMo]

5 minutes ago, Marvin said:

Adding to this is using power from PV installed on the same building. Something difficult to emulate using a gas boiler!

I have that with my combi, so it's not that difficult, just have a cylinder upstream of the boiler, with an immersion.  During the summer some days I used zero gas, most days nothing much for DHW as it was heated by solar PV.

 

Not as effective as a 3-4 CoP but it can be done, with a CoP of 1.

[Marvin]

1 minute ago, JohnMo said:

I have that with my combi, so it's not that difficult, just have a cylinder upstream of the boiler, with an immersion.  During the summer some days I used zero gas, most days nothing much for DHW as it was heated by solar PV.

 

Not as effective as a 3-4 CoP but it can be done, with a CoP of 1.

I like that! learnt something new again!

[JohnMo]

Just now, Marvin said:

I didn't know a boiler could be over 100% efficient. How does it produce more energy than the gas inputs? Is that because of the heat produced through the electrical componants?

It extracts latent heat from the condensation, that is formed in the exhaust, hence the term condensing boiler.  Any temp below I think a return of 53 degs, gives an uplift in efficiency, the lower the temperature the better the efficiency.

 

A gas boiler while firing, with no steam coming out is condensing. 

[Marvin]

On 26/10/2022 at 17:34, Green Power said:

See separate comment below for sources. Use the symbols * # ^ to find the relevant source.

 

This is a comparison of the total forecast lifecycle cost of the heat pump I've just installed, vs the hypothetical gas boiler that I didn't install.

This is for my 2-bed end terrace of 71 square meters*. Air to water for heating and hot water. A 50 year old house with cavity wall insulation in one wall and loft insulation.

 

I have previously discussed this in the separate thread "Boiler Upgrade Scheme Grant - Actions to Take Now."

 

Based on a heating system lifetime of 13 years. Since the gas boiler is more likely to need immediate replacement after about 13 years, and the heat pump is more likely to last longer**, the 13-year time may be slightly favourable to gas. A 20-30 year view looks even better for heat pumps.

 

Daikin: internal unit is model number EHVH04SU18E6V and has a 6kW backup immersion heater and a 180-litre tank. The external unit is ERGA06EVA and has a nominal heating capacity of 5.90kW.

Overview
I estimate £1,105 more up front on the heat pump and then £100 per year saved on service/maintenance after that and £369 saved on fuel (including avoided gas standing charge) for a 2-3 year payback period.

Gas Boiler Costs
£2,300 for boiler ***(including boiler itself, labour and VAT)
£15,516 for gas (13 years at £1,194 per year based on 11588kWh**** per year at £0.103 per kWH#).
£1,330 additional for standing charge (£102 per year at £0.28 per day#.)
£2,600 for maintenance/service/repairs (£200 per year).##
£130 for 2 gas safety certificates at £65 each. ###
TOTAL: £21,876

Heat Pump Costs
£3,405 for heat pump after grant^ (full installation cost including labour, a heat pump, and a hot water tank)
£12,052 for electricity (13 years at £927 per year based on 2727kWh^^ at £0.34 per kWh#)
£1,300 for maintenance/service/repairs (£100 per year).^^^
£106 for removal of the gas meter.^^^^
TOTAL: £16,863.

Saving after 13 years: £5,013. Break even point 2 years 4 months.

Hi @Green Power Just a thought: You may wish to add the electricity used by a gas boiler to your calculations.

[Marvin]

and so it goes on...

 

A combustion or flue gas analyser is used to measure the efficiency of the combustion process within a boiler. This is not the same as the boiler efficiency as it does not take account of, for example, the heat losses from the case of the boiler. So generally the efficiency stated on the rating plate of the boiler will always be lower than the measured efficiency of combustion.

[SteamyTea]

9 hours ago, Marvin said:

I didn't know a boiler could be over 100% efficient. How does it produce more energy than the gas inputs

Lower and Higher heating values.

https://www.engineeringtoolbox.com/fuels-higher-calorific-values-d_169.html

[billt]

15 hours ago, Green Power said:

It doesn´t have to be 4 though, it only has to be about 3.4 when you allow for gas boiler efficiency. Maybe 3.2 if we accept some reduced repair costs with heat pump.

 

Also, where do you get 44p per kWH?

 

My source is https://www.moneysavingexpert.com/utilities/what-are-the-price-cap-unit-rates-/#tool

which has electricity at 34p not 44p.

 

At 34p, that´s a difference of about 3.4, or 2.9 after allowing for gas boiler efficiency. If we accept some reduced repair costs with a heat pump, even a 2.7 COP might be cost parity.

 

I get 44p form my electricity bill. The off peak rate is lower, but not much use for heating. So taking 90% for boiler efficiency (my boiler runs at low temperatures so 90% is a reasonable assumption) that gives 12p per kWh, so that needs a CoP of 3.6.

 

I'm mad so i will probably change the gas boiler for an ASHP in the not too distant future, however the large capital cost will never be recovered, so it will mainly be done because I don't like gas.

 

At the moment the argument that ASHPs have running cost parity with gas is not credible.

[SteamyTea]

Just now, billt said:

At the moment the argument that ASHPs have running cost parity with gas is not credible

All depends where you are starting from and what you include in the counting.

[Green Power]

14 hours ago, Marvin said:

Hi @Green Power Just a thought: You may wish to add the electricity used by a gas boiler to your calculations.

"The minimum electrical consumption of a gas boiler is 65 watts. This is in the phase of operation of the circular pump, and at the time of electric ignition - 120 W, i.e. almost twice as high. If the fan is on, then it consumes electricity - another 30-35 watts"

 

"Having studied the technical documentation for the products of Bosch, Baxi, Vaillant, Ariston and others, we see that the electric power of floor units is in the range from 100 to 200 W, and floor - from 15 to 160 watts"

 

Source: https://en.exactosystem.com/1584-gas-boiler-power-consumption-how-much-electricity-is.html or https://engineer.decorexpro.com/en/otoplenie/kotly/elektropotreblenie-gazovogo-kotla.html (it looks like one of these is a copy and paste from the other)

 

If the average throughout the year is 4 hours per day of boiler use (this is a guess, let me know if anyone can improve this), and assuming that the use is zero or negligible when turned off (again, a guess) then that's 100W x 4 hours = 400Wh = 0.4kWh x 365 days = 146 kWH/year.

x  34p /kWH = £50/year = £650 over the 13 years.

 

I may update my cost calculation in a new thread next year when I have a real electric meter reading and I can take into account some of your other comments and move some of the data towards the average opinion on here in cases where no better source was found.

Edited October 28, 2022 by Green Power
added quotation marks to make it clearer where I copied and pasted from the cited source

[JohnMo]

So again to compared apples with apples, circulation pumps are on bothe a heat pump and a boiler, in either the pump can be inside the box or outside.

 

Ignition is on for a few or less seconds.

 

Fan will be on almost all the time the boiler is firing.

 

So it's 35w/h X 4 x 180 ( days in heating season.  So nearer £8.50. plus an hour a day for DHW, so about £140 over 13 years

 

So close to £150

[Green Power]

When I say 4 hours per day I mean average throughout the year. Say zero hours in summer, 3 in autumn/spring, and 10 in winter. Average 4.

 

So you have 35W for the fan, the article I posted also lists 65W for a pump, for a total of 100W.

 

Ignition we can probably ignore as negligible.

 

I'm assuming that with a heat pump the circulation pumps' electricity consumption  has already been factored in when people quote heat pump COPs or the total electricity they consume, so doesn't need to be considered separately (but this is a guess).

[Radian]

2 hours ago, Green Power said:

the article I posted also lists 65W for a pump

I don't think you can buy those anymore. Most are under 20W these days. Of course the same should apply to both types of system but I'd be looking carefully in any ASHP produced in China.

[JohnMo]

13 minutes ago, Radian said:

looking carefully in any ASHP produced in China.

Thought they all were these days.

[Radian]

18 minutes ago, JohnMo said:

Thought they all were these days.

I think there's quite a bit of diversity in production around the globe. The Daikin Manufacturing Germany Gmbh factory was set up to re-brand Rotex Products into Daikin for example. Viessmann, Kensa and Vailant all have manufacturing plants in the UK. What I was thinking of were the frequently re-badged generic ASHP's that come out of China. Nothing necessarily wrong with those, I've considered them for my own heating before, but I have seen some with pretty primitive circulators.

[HughF]

3 hours ago, Radian said:

I think there's quite a bit of diversity in production around the globe. The Daikin Manufacturing Germany Gmbh factory was set up to re-brand Rotex Products into Daikin for example. Viessmann, Kensa and Vailant all have manufacturing plants in the UK. What I was thinking of were the frequently re-badged generic ASHP's that come out of China. Nothing necessarily wrong with those, I've considered them for my own heating before, but I have seen some with pretty primitive circulators.

I think if you look at the three big players: Sprsun, PHINX and RMRB, you'll probably get something that's pretty decent. They all make a song and a dance about using Wilo/Grundfoss pumps...

[scottishjohn]

I am not sure if things have changed but last time I spoke to a boiler man he told min temp for boiler  return  water was 55 as lower than that and excessive water vapour  in flue would rot the boiler+ flue  very quickly due to aicds from combustion  would be liquid 

Edited October 28, 2022 by scottishjohn

[Radian]

9 minutes ago, scottishjohn said:

I am not sure if things have changed but last time I spoke to a boiler man he told min temp for boiler  return  water was 55 as lower than that and excessive water vapour  in flue would rot the boiler+ flue  very quickly due to aicds from combustion  would be liquid 

Not heard that before, but as I keep pointing out, in a system boiler with no separate setting for HW, a return of 55^oC might limit HW to no more than 45^oC as it would take forever to fully exchange the primary water temperature.

[scottishjohn]

3 minutes ago, Radian said:

Not heard that before, but as I keep pointing out, in a system boiler with no separate setting for HW, a return of 55^oC might limit HW to no more than 45^oC as it would take forever to fully exchange the primary water temperature.

that is obtained by mixing output waterof boiler with return water if lower than 55c to get it up to the 55c  or more

 so running at boiler output temp of 35c -- its always going to be a very strong acid solution in the flue system  and even stainless steel will corode with that 

 

[JohnMo]

18 minutes ago, scottishjohn said:

I am not sure if things have changed but last time I spoke to a boiler man he told min temp for boiler  return  water was 55 as lower than that and excessive water vapour  in flue would rot the boiler+ flue  very quickly due to aicds from combustion  would be liquid 

That may be true for a non condensing boiler, but since 2005 it has been illegal to sell or install a non condensing boiler.  If you boiler is older than that it may be true.  If newer than that he is talking rubbish and really needs to get his facts in line with technology from 20 + years ago.

[scottishjohn]

1 minute ago, JohnMo said:

That may be true for a non condensing boiler, but since 2005 it has been illegal to sell or install a non condensing boiler.  If you boiler is older than that it may be true.  If newer than that he is talking rubbish and really needs to get his facts in line with technology from 20 + years ago.

he was talking about a condensing boiler   to my remberance of the conversation

[JohnMo]

3 minutes ago, JohnMo said:

That may be true for a non condensing boiler, but since 2005 it has been illegal to sell or install a non condensing boiler.  If you boiler is older than that it may be true.  If newer than that he is talking rubbish and really needs to get his facts in line with technology from 20 + years ago.

Direct cut and paste from a condensing boiler manual.

 

"The boiler is equipped with a compact stainless steel heat exchanger with smooth pipes. It is a well thought-out principle using sustainable materials.

The boiler burns (natural) gas to supply heat. This heat is transferred in the heat exchanger to the water in the CH installation. The rapid cooling off of the flue gases causes condensation. This results in a very high efficiency. The condensate that is formed, has no negative impact on the heat exchanger and it's operation, and is removed through the internal syphon."

[scottishjohn]

4 minutes ago, JohnMo said:

Direct cut and paste from a condensing boiler manual.

 

"The boiler is equipped with a compact stainless steel heat exchanger with smooth pipes. It is a well thought-out principle using sustainable materials.

The boiler burns (natural) gas to supply heat. This heat is transferred in the heat exchanger to the water in the CH installation. The rapid cooling off of the flue gases causes condensation. This results in a very high efficiency. The condensate that is formed, has no negative impact on the heat exchanger and it's operation, and is removed through the internal syphon."

If you say so 

but my experience of very low exhaust temps on motor vehicles ,even when fitted with s/s exhaust parts  would not agree with  that 

hydro carbons and water make acid .

I have never seen a boiler stat that goes down to anywhere close to 35c   

Edited October 28, 2022 by scottishjohn