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Thread: Air source heating

  1. #1
    Senior Member Quattromike's Avatar
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    Air source heating

    Just bought myself a new house and it has air source heat pump, as far as I can make out it's approximately 14 years old and the previous tenant said it's inadequate to heat he house and the hot water is Luke warm. Anybody had any experience with them? Do I bother spending money getting it fixed up or do I just forget about the air source and get a proper oil boiler in?
    "At the end of the day, I think it's going to get very dark."

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    Re: Air source heating

    Quote Originally Posted by Quattromike View Post
    Just bought myself a new house and it has air source heat pump, as far as I can make out it's approximately 14 years old and the previous tenant said it's inadequate to heat he house and the hot water is Luke warm. Anybody had any experience with them? Do I bother spending money getting it fixed up or do I just forget about the air source and get a proper oil boiler in?
    Is it coupled up to an old Rad type heating system?
    I understand there is a limit to the max temp that can be achieved with air or ground source.....so you really need to be using underfloor heating etc.

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    Senior Member Quattromike's Avatar
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    Re: Air source heating

    The system has been in for approx 14 years and there is no underfloor heating system just radiators. Everything I look up seems to lead to there are almost adequate if everything is setup right but if not it just costs you money in electricity to run the compressor.
    "At the end of the day, I think it's going to get very dark."

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    Re: Air source heating

    Quote Originally Posted by Quattromike View Post
    The system has been in for approx 14 years and there is no underfloor heating system just radiators. Everything I look up seems to lead to there are almost adequate if everything is setup right but if not it just costs you money in electricity to run the compressor.
    Hmmm
    From what I gleaned a year of two ago when comparing Biomass boiler with Underground....air source etc.......Biomass just provides heat ....as much as you want and probably more.
    Ground and Airsource need a purpose built building, solid floors with loads of insulation underneath the an underfloor heating system. This allows you to build up a heat store within the floor.....effectively virtually no heat loss due to the insulation and a small amount of heat being pumped in 24 hrs a day.....over time temp rises to let's say to a comfort level. Radiators will provide virtually nil heat store.
    More and more the need for a small turbine + some solar panels etc to generate some electricity to power the pump / Compressor and glean some income for generation from RHI etc becomes apparent......but costs escalate hugely.

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    Senior Member Quattromike's Avatar
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    Re: Air source heating

    I've convinced myself I'm fitting an oil boiler but the question is do I keep what is already there which does produce luke warm water and use the boiler to boost this and potentially save a bit of oil or do I rip it out and fit the boiler only and potentially save on a complicated system that combines the two. Ill need to speak with my plumber in the new year about it but always best to get as much opinions on it
    "At the end of the day, I think it's going to get very dark."

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    Re: Air source heating

    Wondered about that......surely the return temp of the water from rads to the boiler will be higher than the temp from the air source unit.
    Would it be possible to use it to heat DHW only, possibly enlarging the hot water cylinder storage to allow for exploiting day time air temps. Or in anther way pre heating / warming the water that enters the DHW cylinder thus reducing the oil consumption? Probably not a huge saving......would it perhaps provide hot water during the summer? Thus saving some summer time oil.....I suspect that if oil was 75p / 1 per litre the topic would be viewed in a rather different way.

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    Senior Member Quattromike's Avatar
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    Re: Air source heating

    I've decided the air source is comin out and oil fired is going in, I'll have to change the hot water tank also as it's a combined unit
    just out of interest is there any plumbers on here that could give me an idea of boiler size?
    I think it'll be a grant vortex system boiler , the house is 152 m2 . I'm thinking 26-28 kw but that is a huge guess
    "At the end of the day, I think it's going to get very dark."

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    Re: Air source heating

    Work your way around the house with this
    http://www.diy.com/help-advice/btu-r...art_100006.art
    Pretty accurate, total up the required Btu's and there is your answer....with a bit added on for a safety margin.
    Worked for me......Google central heating ....Radiator sizing etc loads of stuff online.j

    Oh yes and you need a bit for DHW.....again a bit of googling will provide the answer.
    Last edited by Gee; 10-01-17 at 05:42 PM.

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    Re: Air source heating

    Quattromike
    on this side of the pond, my father had 3 hot water heating systems in his house
    1. an electric hot water heater for domestic hot water
    2. an oil boiler for hot water and heating the house
    3. a wood boiler for hot water and heating the house

    and he NEVER used all of them at the same time

    In the middle of the summer, he would have the wood and oil shut down (didn't need to heat the house) and just used the electric heater for domestic water.
    In the fall when he needed a little bit of heat during the night and first thing in the morning, he would start the oil boiler and shut off the electric heater.
    In late fall / early winter when he needed heat most of the day, he would shut off the oil boiler and start the wood boiler.
    He would keep the wood boiler going until he didn't need heat all day, then revert back to the oil boiler and by summer he would be using only the electric water heater.

    Long story short, since you already have the system, will it provide the heat you need for some parts of the year at a more cost-effective price point than burning oil?

  10. #10
    Senior Member Quattromike's Avatar
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    Re: Air source heating

    I hear what your saying, use wot I got and I've been thinking about the cost of running. Air source heat pumps are said to turn 1kw of electricity into 3kw of heat. So approx 18p per unit means 6p per kw of heat and not enuff heat when required at that. Oil boilers are approx 95% efficient these days turning oil into heat so 1 litre cost 42p and produces 1kw for 4p of adequate heat. Also I'm thinking oilboilers are simple and the local plumbers will fix it if broke but they won't look at a heat pump system and have to get a specialist to come from afar which is costly.
    "At the end of the day, I think it's going to get very dark."

  11. #11
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    Re: Air source heating

    I have a Water Source Heat Pump on the main house, and a ASHP on the pool for the cottages and self specified everything - and mine work great. But they do require some knowledge.

    I think there are a few separate issues:

    ASHP Size
    Is it big enough? Was it ever big enough? At 14-years old it has been in some time. It is possible that it was sized small to reduce capital outlay required with the knowledge of the owner that it may need backing up with additional heat at the coldest times (e.g. open fire/wood burner). That doesn't make it wrong, it just makes it a different strategy for delivering heat. Also has the house size changed?

    You need to do the heat calculations for your house and compare this to the output of the ASHP. If it is big enough then it is radiator size that limits it, if it isn't big enough then what do you expect it do?


    Water Temp
    Our ASHP is capable of delivering up to 55 DegC, others less, but it is less efficient the hotter you want. Our hot water runs at 45 Deg C which is just hot enough to be hot but doesn't make topping a bath up that viable. Once you get used to not burning yourself on hot water it is actually much nicer (don't start the salmonella stuff -it has never been found in residential and we occasionally heat with immersion). In fact 39 DegC is a sensible end use temperature.

    Radiators
    We have an old farmhouse with a conversion to include the old mill room. It was converted in 1990 (not by us) but we did install underfloor heating in the old mill part but the main farmhouse is on radiators connected to a water source heat pump. It is fine at an average of 0 Deg C and was specified to handle down to -5DegC based on theoretically losses for each room. After that it will struggle to match heat input with heat losses. Partly because I'm at the limit of two single phase GSHP units and a third was overkill. Increasing some radiator sizes (or changing to modern ones) would help but we haven't done it yet. But yes it can run a large 5-bed farmhouse on radiators. Underfloor heating is better as the source temperature can be dropped further, making it more efficient. Anything below -5DegC for a sustained period and we will have to put the log burner on which has a back boiler to a central radiator to dump heat or stick another heater but figure this a couple of weeks every few years only.

    The system compensates for outside temperature so if i only coolish the radiators are only luke warm but the GSHP is at its most efficient.

    So they can work with radiators but the bigger the better. You can look up the heat output for all old radiator sizes and compare with output capacity of ASHP and heat loss from building calcs.


    Is it faulty?

    We used to have an old ASHP (25-years) on the pool with two compressors. One had a fault so it wouldn't work very well if really cold when it needed to use both compressors to generate hot heat. So anything below 1 or 2 Deg C and it struggled (but would have been fine if both compressors worked). It got replaced with a new one. So it can still work but may still be faulty!


    What next
    So if your ASHP system isn't up to the job then it is one of four things:
    • The ASHP was never big enough
    • The radiators aren't big enough
    • They had a plan for using alternative heat
    • It has a fault


    Do the energy calcs for the building, work out the radiator output and you will have your answer. Note installing a oil boiler that is too small or has inadequate radiators would also cause the same problems! Although with higher temps of oil boiler it is less likely to be the radiators.

    If the house was sold it will have with an EPC then this will be a rough guide to energy required to heat the house - but not as good as doing the calls yourself properly.

    Then look at ASHP and GSHP options to see what RHI payments you may get. Modern ASHP units are more efficient than old ones.

    Our WSHP cost 23,000 and brings in 8,400pa for 7-years on RHI plus it costs half what LPG cost despite having it on from 4am until 10pm. (LPG cost based on what I paid, WSHP based on electric meter feeding it and only it).

  12. #12
    Senior Member Quattromike's Avatar
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    Re: Air source heating

    I've decided to fit the oil boiler , have it sitting ready to go just need the plumber to pull finger out and get on with it. Any payments went with whoever installed the system 12 years ago. 265 a month it cost to run the heating system in Jan/Feb and that was set low and not all that comfortable. I realise there could be an issue with the system and it may not be as efficient as it should but local plumber don't want to touch it and my mind was made to change it so never did anything about it. As ever it looks like the new system will not be in until the milder weather comes
    "At the end of the day, I think it's going to get very dark."

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    Re: Air source heating

    Quote Originally Posted by Quattromike View Post
    Any payments went with whoever installed the system 12 years ago.
    No payments available 12-years ago. RHI (Renewable Heat Incentive) has only been going for 3-5 years, similar to FiTs for PV. Payments on ASHP even less, just last two years. Just checked inflation linking and we get 8700 up from 8400 pa next year - Yippee!


    Quote Originally Posted by Quattromike View Post
    I've decided to fit the oil boiler , have it sitting ready to go
    Just hoped it isn't undersized. If it isn't specified right then further trouble will come. Of course it is always easy to over specify, have a system that costs too much and operates outside of its efficiency zone. Sizing them right is harder - and heat calculations are the only way. It is what a heating engineer does - but not all plumbers are heating engineers.


    Quote Originally Posted by Quattromike View Post
    265 a month it cost to run the heating system in Jan/Feb and that was set low and not all that comfortable.
    We spent 1500pa on LPG (not hot water or cooking) so would be in excess of 265/month but properties vary.

    Quote Originally Posted by Quattromike View Post
    local plumber don't want to touch it
    He probably won't touch your electrics either. My local plumber won't touch my GSHP either, but he is a good plumber. They are more complex, well a GSHP is, but an ASHP is no more complex than a combination really.

    There is a heat pump in the back of your fridge, running backwards - a cold pump if you like.


    But they aren't for everyone and do need specifying right from the outset. Hope the oil boiler keeps you warm.

    DG

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    Senior Member Quattromike's Avatar
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    Re: Air source heating

    Me too
    "At the end of the day, I think it's going to get very dark."

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