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New Build swap from Gas -> A2W

  • 13-12-2019 4:02pm
    #1
    Registered Users Posts: 714 ✭✭✭ BuzzFish


    Hi Folks,

    I'm hoping someone can help a little here. Any feedback would be really appreciated.

    I've agreed to buy a new A3 rated home which has been constructed to the point it's just about to start 1st fix. No pipework or wiring has been installed as yet. but the internal studding is completing out.

    The house is spec'd with a gas boiler and I want to upgrade to a A2W system. The builder has suggested this could add 10k to the cost but is looking at numbers and making calls.

    My question is... what could I reasonably expect would be the cost difference between a gas boiler system and a A2W set up when installed at this point of the build?

    The house is 2100Sqft over 3 stories. 4 bedroom.


Comments

  • Registered Users Posts: 11,197 ✭✭✭✭ KCross


    Not sure on your cost question, but if the gas heating system is based on radiators, switching to A2W isnt ideal.

    It should really be underfloor heating for heat pumps to get the most out of them.


  • Registered Users Posts: 188 ✭✭ Latro


    200sqm @ A3 is perfect for medium size A2W.

    7KW unit would be ideal for you. Do not go higher than single phase 9kW unit. It will be overkill and 3 phase installations add substantially to the costs. 7kW unit pumps up to 168kWh of heat energy per day. With A3 rating you are unlikely to even approach this level in the coldest periods of any Irish winter.

    If still possible go with underfloor downstairs but if it's too late you will be fine with all double (or triple but more expensive) panel rads as long as they are a bit oversized.

    I pessimistically predict heating cost of 400-450 euro per year. 350ish or less likely.

    The whole installation should not cost you much more than gas.
    Monoblock units are extremely simple to install. In fact it is far easier than gas but for some reason it is still treated like rocket science.
    I assume it is easier to rip people off this way. I assure you that half decent plumber could do it only by following installation manual.

    All you need is a solid, raised base, not obstructed air flow, sufficient diameter of water pipes for flow and return, sufficient size of mains cable and good drainage for condensed water from the evaporator.

    From pluming point of view it is no different than oil/gas installation minus the whole liquid fuel supply side, plus beefy electrical connection similar to average 10kW electric shower. Some units even have circulation pump and filters all contained within the block.

    7-9kW unit of the industry leading brands will set you back by 4-5k. Mitsubishi, Daikin, Panasonic, LG, Samsung etc they are all very good. Do not buy cheap unknown brands.

    Pipes, extra magnetic filter etc are hardly different from earlier mentioned types of heating so the cost is the same here.

    If possible install away from your or your neighbor bedrooms. Good HPs are not loud at all but could annoy an odd oversensitive person on colder nights.


  • Registered Users Posts: 714 ✭✭✭ BuzzFish


    Latro wrote: »
    200sqm @ A3 is perfect for medium size A2W.

    7KW unit would be ideal for you. Do not go higher than single phase 9kW unit. It will be overkill and 3 phase installations add substantially to the costs. 7kW unit pumps up to 168kWh of heat energy per day. With A3 rating you are unlikely to even approach this level in the coldest periods of any Irish winter.

    If still possible go with underfloor downstairs but if it's too late you will be fine with all double (or triple but more expensive) panel rads as long as they are a bit oversized.

    I pessimistically predict heating cost of 400-450 euro per year. 350ish or less likely.

    The whole installation should not cost you much more than gas.
    Monoblock units are extremely simple to install. In fact it is far easier than gas but for some reason it is still treated like rocket science.
    I assume it is easier to rip people off this way. I assure you that half decent plumber could do it only by following installation manual.

    All you need is a solid, raised base, not obstructed air flow, sufficient diameter of water pipes for flow and return, sufficient size of mains cable and good drainage for condensed water from the evaporator.

    From pluming point of view it is no different than oil/gas installation minus the whole liquid fuel supply side, plus beefy electrical connection similar to average 10kW electric shower. Some units even have circulation pump and filters all contained within the block.

    7-9kW unit of the industry leading brands will set you back by 4-5k. Mitsubishi, Daikin, Panasonic, LG, Samsung etc they are all very good. Do not buy cheap unknown brands.

    Pipes, extra magnetic filter etc are hardly different from earlier mentioned types of heating so the cost is the same here.

    If possible install away from your or your neighbor bedrooms. Good HPs are not loud at all but could annoy an odd oversensitive person on colder nights.

    Thank you so much for this. Very informative and helps me have a good conversation with the builder.


  • Registered Users Posts: 10,925 ✭✭✭✭ Calahonda52


    BuzzFish wrote: »
    Thank you so much for this. Very informative and helps me have a good conversation with the builder.

    Informative perhaps but accurate no.

    Rads for a HP will be substantially larger due to the difference the the Delta T between gas and the Heat pump.
    .
    The idea that a plumber can properly [ install, commission and service] a heat pump with no training is .....x
    I think you will find
    that on the better kit, it will impact your warranty.
    This is especially true for UFH, how will they design the pipework, flow rates, set points etc.
    .....x
    .
    The heat pump to buy is more expensive that the boiler, the rads are more expensive.
    Ideally you should have a buffer tank to maximise the use of night rate


  • Registered Users Posts: 188 ✭✭ Latro


    All that I wrote above is 100% based on my own experience.

    "Rads for a HP will be substantially larger due to the difference the the Delta T between gas and the Heat pump."
    The statement is true but you would not run gas 24/7 like you would HP.
    You simply trade off radiator power for time.
    Lets say the heat demand is 20kWh per day. With oil or gas you would run 5000W radiators for total of 4 hours spread across the day to compensate for the heat loss.
    With heat pump lets say the same radiators will operate at 1/5th of the above because of lower water temperature but you will run it 5 times longer. The result is the same, 20kWh was compensated. In the second case you will achieve better comfort. The room temperature will be constant all the time.


    "Ideally you should have a buffer tank to maximize the use of night rate"
    Are you sure? I disagree but I'm open to be proven wrong.

    Do you realize how big the buffer would have to be? Probably 5000L would be considered too small. Don't forget that heat pump produces low temperature water, 30-40 degrees. Just research and calculate yourself how much heat energy is stored in 5000L at delta T = 10. You will be surprised how little it is.

    Adding those buffers will unnecessary add substantially to cost, it would add another layer of complexity and would make the system less efficient.
    Extra pump, pipes, heat loss from massive buffers, large room needed for all the above. I would not recommend it, it is not worth it.
    The simpler the better. Just hook it up straight into the manifolds like you would with gas and balance everything the same way, there is no difference.

    I went through the same dilemma and even plumbed for optional future buffer just in case but now I don't see the point. With already very low heating cost there is no need to push for more savings. It would generate negative ROI. Also during nights the temperature tends to drop, there is less heat energy available and the pump has to work harder. I really doubt that the whole night rate exercise would give any noticable savings considering a lot of your electricity for other devices would be consumed on more expensive day rate.


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