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  • FIRST POST
    • blizeH
    • By blizeH 3rd Oct 19, 1:34 PM
    • 1,281Posts
    • 583Thanks
    blizeH
    With gas boilers potentially being banned in new homes from 2025, should we look at alternatives now
    • #1
    • 3rd Oct 19, 1:34 PM
    With gas boilers potentially being banned in new homes from 2025, should we look at alternatives now 3rd Oct 19 at 1:34 PM
    We need to replace our boiler ASAP and I'm wondering if it's worth looking at heat/air pumps? They're very expensive on the up front cost but it looks like in the (very) long run the savings make it worthwhile?


    I'm a bit concerned about the work involved though, and the physical space it uses. Any thoughts please? Thanks
Page 1
    • markin
    • By markin 3rd Oct 19, 2:59 PM
    • 877 Posts
    • 730 Thanks
    markin
    • #2
    • 3rd Oct 19, 2:59 PM
    • #2
    • 3rd Oct 19, 2:59 PM
    This is the thread you want to read, over in LPG, Heating Oil, Solid & Other Fuels


    Air Source Heat Pumps/Air Con - Full Info & Guide
    https://forums.moneysavingexpert.com/showthread.php?t=1464827
    • Reed_Richards
    • By Reed_Richards 3rd Oct 19, 7:28 PM
    • 606 Posts
    • 371 Thanks
    Reed_Richards
    • #3
    • 3rd Oct 19, 7:28 PM
    • #3
    • 3rd Oct 19, 7:28 PM
    Heat pumps work best if you have underfloor heating because you can use water at a lower temperature.
    Reed
    • Ectophile
    • By Ectophile 3rd Oct 19, 8:59 PM
    • 3,871 Posts
    • 2,532 Thanks
    Ectophile
    • #4
    • 3rd Oct 19, 8:59 PM
    • #4
    • 3rd Oct 19, 8:59 PM
    Personally, I would get a gas boiler while they are still readily available. I don't think they are going to ban existing gas boilers for a very long time.
    If it sticks, force it.
    If it breaks, well it wasn't working right anyway.
    • ASavvyBuyer
    • By ASavvyBuyer 10th Oct 19, 11:32 AM
    • 1,060 Posts
    • 3,101 Thanks
    ASavvyBuyer
    • #5
    • 10th Oct 19, 11:32 AM
    • #5
    • 10th Oct 19, 11:32 AM
    Found a reference to this on another site. https://www.boxergy.com/product

    A heat pump that uses stored electricity and heats the water to normal central heating temps, so can be used to replace a gas boiler.

    No details on cost, but expect there will be similar heat pumps about and in future.
    Rhondda Cynon Taf, 4kWp, W roof, 30 pitch, 16 x 8.33 Eternity 250w E+10 panels, Solar Edge SE4000-16A Inverter + P300 Optimisers. Inst Aug 2015.
    REUK Diverter, Toshiba RAS-10G2KVP-E Ultra High Efficiency Air Conditioner/Heat Pump, Kia Soul EV & 100% Green Electric Tariff.
    • michaels
    • By michaels 10th Oct 19, 12:43 PM
    • 22,909 Posts
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    michaels
    • #6
    • 10th Oct 19, 12:43 PM
    • #6
    • 10th Oct 19, 12:43 PM
    I have been thinking about this although our boiler hopefully has a few years left. The issue with heat pumps seems to be the requirement for lower temps to acheive sensible efficiency resulting in a requirement to replace all rads and pipework and even then it is unclear whether an average cop of 4 needed to make the cost competitive with gas can actually be achieved.

    Gshp has a higher fit and more stable cop but the numbers only seem to work for trench install which we don't have space for even before the cost of a replumb.

    Battery/large hot water tank storage of cheap overnight leccy plus individual room ashp might give different numbers again....
    Cool heads and compromise
    • GreatApe
    • By GreatApe 10th Oct 19, 1:02 PM
    • 4,016 Posts
    • 2,969 Thanks
    GreatApe
    • #7
    • 10th Oct 19, 1:02 PM
    • #7
    • 10th Oct 19, 1:02 PM
    I have been thinking about this although our boiler hopefully has a few years left. The issue with heat pumps seems to be the requirement for lower temps to acheive sensible efficiency resulting in a requirement to replace all rads and pipework and even then it is unclear whether an average cop of 4 needed to make the cost competitive with gas can actually be achieved.

    Gshp has a higher fit and more stable cop but the numbers only seem to work for trench install which we don't have space for even before the cost of a replumb.

    Battery/large hot water tank storage of cheap overnight leccy plus individual room ashp might give different numbers again....
    Originally posted by michaels

    You should be able to buy electricity at wholesale rates
    In which case you'd pay about 4-5p average
    And a heat pump would be very viable

    A fixed line rental plus wholesale price for each unit makes sense and will allow the country to electrify heating much more rapidly and allow deployment of offshore wind power much more rapidly

    Output also at least on a seasonal basis has some correlation
    With offshore wind output 50% higher during the cold months than the warm months

    The fixed line rental can be based on the property EPC rating but would be about 30 on average
    With lower efficiency properties paying higher lone rental and more efficient less line rental
    • ABrass
    • By ABrass 10th Oct 19, 1:12 PM
    • 217 Posts
    • 294 Thanks
    ABrass
    • #8
    • 10th Oct 19, 1:12 PM
    • #8
    • 10th Oct 19, 1:12 PM
    It depends, the price of GSHP and to a lesser degree ASHP will fall given time (R&D) and as a result of increased market penetration. There was talk about purpose built drilling systems that hit a better value for money point on bored systems.

    On the other hand the RHI won't last forever and if you can qualify for it then it makes a huge difference to payback times.

    If you've got cash laying about then I'd say yes do it now. But if you're trying to retrofit into an older property it's an epic job. I've got it pencilled in for 2021 or 2022.
    • Martyn1981
    • By Martyn1981 10th Oct 19, 1:20 PM
    • 9,619 Posts
    • 14,513 Thanks
    Martyn1981
    • #9
    • 10th Oct 19, 1:20 PM
    • #9
    • 10th Oct 19, 1:20 PM
    I have been thinking about this although our boiler hopefully has a few years left. The issue with heat pumps seems to be the requirement for lower temps to acheive sensible efficiency resulting in a requirement to replace all rads and pipework and even then it is unclear whether an average cop of 4 needed to make the cost competitive with gas can actually be achieved.

    Gshp has a higher fit and more stable cop but the numbers only seem to work for trench install which we don't have space for even before the cost of a replumb.

    Battery/large hot water tank storage of cheap overnight leccy plus individual room ashp might give different numbers again....
    Originally posted by michaels
    Apologies for pedantry, but in the UK, ASHP's (air to water) average a COP of 2.9, but, I'd suggest that that is close to 4x when you take gas boiler efficiencies into account.

    But, cheap rate leccy, and at least some PV leccy will improve the figures further, so a straight day rate v's gas isn't wholly the best comparison.


    The idea here looks interesting, but I assume the heat battery part is effectively running at a COP of about 1, which raises the question, why not run the ASHP longer/harder with lower rad temps and benefit from the COP advantage? I assume the answer is simply that this is a compromise solution for those (myself included) where more work would be needed for a normal ASHP.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • michaels
    • By michaels 13th Oct 19, 4:12 PM
    • 22,909 Posts
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    michaels
    So I am trying to do the maths.

    Let us exclude purchase and install cost for now (assume it will be covered by RHI) for the sake of simplicity.

    WE currently use 32000 kwh of gas a year.
    Looking at monthly usage I am guessing about 1000kwh per month for hot water and up to 4000kwh for heating in the coldest months. I straight divide gives daily usage of 133kwh or 5.5kwh per hour but of course individual days might be even colder so we might need constant heat output of 8kwh per hour on the coldest days.

    I don't know how efficient our boiler is - in theory it is condensing and modulating so will mostly run at its most efficient. It can output between 5kw and 19kw, the heating curve has a return water temp for heating of 30C when the outside temp is 10 degrees up to 70C when it is minus 10.

    First issue is therefore obvious - heat pumps are not efficient with water temps of 45 degrees (?) suggesting that our heat emitters (radiators) are not sufficient for the water temp. We could obviously upsize to improve heat output at lower water temps (change doubles to triples etc) but it is still unclear if this would be sufficient and then there is still the question of circulation - I know a fair bit of the upstairs is only 15mm pipe not 22mm.

    Our hot water tank is 190l which we heat to 60 degrees. In an hour in the morning we typically run off one bath and 5 showers - say 4-500l? If the incoming water temperature is 15 degrees that means we drain the whole tank and also use a fair bit of the boiler output to achieve this. (approx 12kwh stored in the tank plus 5kwh from the boiler to provide 17kwh worth of hot water from 15 degrees to 40 degrees).

    If the boiler is cooler (to max heat pump efficiency) then obviously we would need to provide more of the heat 'on the go'. There is also the question of legionella if the water tank is not at least 60C once a day.

    So it looks like we might need either a bigger hot water cylinder or heat pump output of at least 19kw as we have now with the gas. At a COP of 1 (coldest days or direct electric back up) this is 80A which might be a problem with a 100A supply and other use.

    Putting all this heat demand together means we might need a heat pump system able to output at least 12-15 kwh per hour however cold it is outside.

    WE pay about 3p per kwh for electricity and 12p per kwh for gas. The big question is then what are the relative efficiencies. For heat pumps this info seems pretty thin on the ground for either ashp or both types of gshp. it is also unclear what the losses are for gas hot water and heating.

    Is COP 3 for ashp, 3.5 for ground trench and 4 for ground vertical loop reasonable? How about for the efficient gas boiler - 90%?
    32000 x 90% = 28,800 output demand
    32,000 x 3p = 960
    28,800/3 (COP) = 9,600 x 12p = 1152
    28,800/3.5 (COP) = 8,230 x 12p = 990
    28,800/4 (COP) = 7,200 x 12p = 864

    Given the amount of energy involved there seems to be very little scope for time shifting demand to off peak electricity rates using battery storage. Even storing the hot water heat in a large hot water cylinder seems to have limited scope due to the lower temperatures for high efficiency.

    So the only thing that seems to make sense might be a vertical loop gshp, problem with this is the install cost, high 20k plus whatever is needed to make the radiators work and address the legionella issue with an RHI that seems to be at most 20k over 7 years.
    Cool heads and compromise
    • Solarchaser
    • By Solarchaser 13th Oct 19, 5:02 PM
    • 199 Posts
    • 264 Thanks
    Solarchaser
    To get rid of the legionella issue, go for a 500l heat store instead, so the water is never stagnant, it just flows through the coil, the "dirty water" is heated instead, and transfers heat to the potable water through the coil.

    That's what I'll be going for.
    • Martyn1981
    • By Martyn1981 13th Oct 19, 5:09 PM
    • 9,619 Posts
    • 14,513 Thanks
    Martyn1981
    Holy methane burping cows Batman!

    32,000kWh's of gas per year, how? And 1,000kWh's for DHW per month - I appreciate I don't smell like a rose, and there are only two of us, but our gas consumption for the last 6 months has been ~500kWh (46 units), and that includes the oven.

    Anyways, back to the costs, remember that with a heat pump you'd be running it at night in your situation, so some of that leccy consumption would be cheap rate, and ideally, you might try to run it harder at night and lower during the day, when possible. Plus some PV, though for you that might be negligible.

    Personally, I'm at the opposite end, as our heating was able to cope, but we have since improved insulation, and at every opportunity replaced rads with double plus ones, and longer if possible, so a heat pump would hopefully be viable, though we have to replace all the microbore with 15/22mm, but I ensured that access to all pipework and wiring would be easy(ish) when it was overhauled 20+yrs ago. For us, the hope would be to make greater use of cheap rate leccy, and some steep south faced PV panels would make a noticeable contribution during the day.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
    • silverwhistle
    • By silverwhistle 13th Oct 19, 5:44 PM
    • 2,734 Posts
    • 4,108 Thanks
    silverwhistle
    That does seem a lot of gas. I wish I could calculate the kWh value of the wood I burn as my annual gas consumption is only 1000. Nothing in the last six months (all cooking by electric). Value of the scrounged wood is virtually nil: petrol for half a mile and my labour costs, which are cheap!



    The economics on any capital investment for me, with a terrace house, are even more difficult to justify.
    • michaels
    • By michaels 13th Oct 19, 8:50 PM
    • 22,909 Posts
    • 104,748 Thanks
    michaels
    To get rid of the legionella issue, go for a 500l heat store instead, so the water is never stagnant, it just flows through the coil, the "dirty water" is heated instead, and transfers heat to the potable water through the coil.

    That's what I'll be going for.
    Originally posted by Solarchaser
    Interesting - I did a system like that before in our previous house although not nearly 500l.

    Would this allow you to more efficiently use an inline direct electric heater to boost the temp above the store temperature which is optimised for heat pump?
    Cool heads and compromise
    • michaels
    • By michaels 13th Oct 19, 9:09 PM
    • 22,909 Posts
    • 104,748 Thanks
    michaels
    Holy methane burping cows Batman!

    32,000kWh's of gas per year, how? And 1,000kWh's for DHW per month - I appreciate I don't smell like a rose, and there are only two of us, but our gas consumption for the last 6 months has been ~500kWh (46 units), and that includes the oven.

    Anyways, back to the costs, remember that with a heat pump you'd be running it at night in your situation, so some of that leccy consumption would be cheap rate, and ideally, you might try to run it harder at night and lower during the day, when possible. Plus some PV, though for you that might be negligible.

    Personally, I'm at the opposite end, as our heating was able to cope, but we have since improved insulation, and at every opportunity replaced rads with double plus ones, and longer if possible, so a heat pump would hopefully be viable, though we have to replace all the microbore with 15/22mm, but I ensured that access to all pipework and wiring would be easy(ish) when it was overhauled 20+yrs ago. For us, the hope would be to make greater use of cheap rate leccy, and some steep south faced PV panels would make a noticeable contribution during the day.
    Originally posted by Martyn1981
    The maths says 1000 litres per day (10 showers and 2 baths) heated from 15 degrees to 45 degrees is 41kwh times 30 days is 1230 kwh per month.
    Cool heads and compromise
    • Cardew
    • By Cardew 13th Oct 19, 9:25 PM
    • 27,994 Posts
    • 13,844 Thanks
    Cardew
    I don't know how many million families live in flats in UK, but for many of them Heat Pumps(all types) are impractical. Apart from the noise issue how do you mount and access the units on, say, a 20 storey block?
    • 1961Nick
    • By 1961Nick 13th Oct 19, 9:35 PM
    • 1,107 Posts
    • 3,666 Thanks
    1961Nick
    Holy methane burping cows Batman!

    32,000kWh's of gas per year, how? And 1,000kWh's for DHW per month - I appreciate I don't smell like a rose, and there are only two of us, but our gas consumption for the last 6 months has been ~500kWh (46 units), and that includes the oven.
    Originally posted by Martyn1981
    5 showers & 1 bath per day suggests a household of 6 persons & therefore a reasonably large house?

    If the above is true, then 32000 kWh doesn't seem unreasonable.

    For comparison, 3 of us managed to consume 27910 kWh of gas last year & we're already up to 17000 this year - now with just 2 of us.
    4kWp (black/black) - Sofar Inverter - SSE(141) - 30 pitch - North Lincs
    Installed June 2013 - PVGIS = 3400

    Sofar ME3000SP Inverter & 5 x Pylontech US2000B Plus Batteries - 12kWh
    • michaels
    • By michaels 13th Oct 19, 9:48 PM
    • 22,909 Posts
    • 104,748 Thanks
    michaels
    5 showers & 1 bath per day suggests a household of 6 persons & therefore a reasonably large house?

    If the above is true, then 32000 kWh doesn't seem unreasonable.

    For comparison, 3 of us managed to consume 27910 kWh of gas last year & we're already up to 17000 this year - now with just 2 of us.
    Originally posted by 1961Nick
    That is correct, although the showers and bath are all twice a day but obviously there is min 7 or 8 hours of cylinder warm up time between each set of 6.

    House is about 170sqm 5 bed semi half built in 1938, the other half in 2010, allegedly EPC B - heating is 24/7 set at 17 degrees at night and 21 in the day but probably generally a bit warmer as this is by weather cop not interior thermostat and monitoring suggests that the coolest room meets the 17/21 threshold.
    Cool heads and compromise
    • 1961Nick
    • By 1961Nick 13th Oct 19, 9:54 PM
    • 1,107 Posts
    • 3,666 Thanks
    1961Nick
    Interesting - I did a system like that before in our previous house although not nearly 500l.

    Would this allow you to more efficiently use an inline direct electric heater to boost the temp above the store temperature which is optimised for heat pump?
    Originally posted by michaels
    An electric water heater fitted after the heat store would boost the hot water temperature. Something like a 10 kWh heater would do the job.

    Here's a random one...

    https://www.screwfix.com/p/strom-seih11kts1-touchscreen-instantaneous-water-heater-11kw/4681p
    4kWp (black/black) - Sofar Inverter - SSE(141) - 30 pitch - North Lincs
    Installed June 2013 - PVGIS = 3400

    Sofar ME3000SP Inverter & 5 x Pylontech US2000B Plus Batteries - 12kWh
    • michaels
    • By michaels 13th Oct 19, 9:59 PM
    • 22,909 Posts
    • 104,748 Thanks
    michaels
    An electric water heater fitted after the heat store would boost the hot water temperature. Something like a 10 kWh heater would do the job.

    Here's a random one...

    https://www.screwfix.com/p/strom-seih11kts1-touchscreen-instantaneous-water-heater-11kw/4681p
    Originally posted by 1961Nick
    Thanks - cop on that is 1 of course and no time shifting to cheaper leccy periods possible.

    What sort of temp can a heat pump heat hot water too before it becomes disastrously inefficient? Does it differ for an ashp that has to contend with very low temps vs a horizontal or even vertical loop gshp?
    Cool heads and compromise
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