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    Has anyone used a portable (reversible) air-con unit as a heater for a garden room for example? If so, how well did it work for you?


    • CommentAuthorowlman
    • CommentTimeJan 15th 2022 edited
    Hi Nick,
    Your question got me thinking and I did a bit of searching and most of the review/feedback seems reasonably positive, albeit mainly from the cooling perspective. Noise seems to be the worst aspect.
    For heating I guess you'd need some form of external air exhaust.
    This one seems interesting.

    Thanks Owlman. Hadn't seen the one in your link but found https://www.cityplumbing.co.uk/12000BTU-3-5kW-Heating+Cooling-Portable-Air-Conditioning-Unit/p/488717 and https://www.aircondirect.co.uk/p/1243754/12000-btu-portable-air-conditioner-for-rooms-up-to-30-sqm-with-heat-pump-and-alexa-wifi-control

    Both seem to have a flexi plastic duct which apparently gets rid of condensate too, but must be the air input to the HP in heating mode, surely. Is that your understanding too?
    • CommentTimeJan 15th 2022
    Surely a heat pump needs both a flow and return? (one of each for both the source and the delivery side) In the case of a monobloc situated entirely indoors then it needs an air intake and an air exhaust duct? Regardless of whether it is in heating or cooling mode. And the might be condensation in both cases that needs to be disposed of.
    djh, that's what I'd have thought, but neither of the models I linked to 'explain themselves' well as far as I can see. The only connection with outside which is mentioned is the flexi-pipe 'hang-it-out-of-the-door type thing.

    I need to find out more as it *may* be a good short-term solution (short of a permanently-fixed split A/A HP) for a client's garden room. Logic tells me that if it's reversible (which these say hey are then a portable unit ought to be able to do a similar job to a 'proper' A/A unit, but I have yet to find out the 'mechanics' of it.
    Isn't it basically an exhaust air heatpump - it blows some room air out through the hose, and pumps heat out of that departing air, which it uses to warm the room? (Or reverse for cooling).

    The exhausted air is presumably replaced by infiltrating air, hopefully not too cold, otherwise there's no net heat gain! This infiltration is not required for a split air-air heatpump.

    You won't want to leave the door open for the hose in heating season, so it will need a hole through the wall?

    Edit to add: as with previous discussions of exhaust air heatpumps, it's only a good idea if the amount of 'through ventilation' it creates is desirable. If you didn't need that much air movement then it erodes the efficiency below the value on the datasheet, because you have to heat up the infiltrating air.
    • CommentAuthorowlman
    • CommentTimeJan 16th 2022 edited
    It seems then that they may be fairly sophisticated bits of kit, at least the good ones, and reflected in price I guess.
    In a domestic environment, waste exhausted heat in the Summer cooling mode is easily disposed of through an open window and a loose hose, and condensate goes into a bucket in the cabinet. In winter warming mode it becomes more complicated, that's maybe why the cheap ones are cooling only.
    I think you're right Will, in heating mode it would need to be plumbed in through a hole in the wall. The diameter of that hole may need to be up to 6" to cope with volume and ultimately heating capacity, I'm guessing.
    That's not to say it couldn't all be done and if the device were sited well and close to the wall that duct run could be very short and with shut off baffles it's easily done.
    I'm sure Nick all that's been thought out, but I'd eyeball the noise aspect as well as the usual efficiencies and warming capacity.
    • CommentAuthorRobL
    • CommentTimeJan 16th 2022
    If holes are ok through the wall, you can get installed fully internal units which have in and out airflows. The whole thing is like a large indoor radiator - these guys have a few of them (others are available). They seem to have cooling only, and also reversible units. Haven’t got or seen one in action, I think marketed at hotels as there’s no box outside.

    Thanks Owlman, W-in-A and RobL. Had typed a 'thankyou' post and lost it. Yes, assumed hole-in-the-wall, and concerned re noise too. Not thought out at all yet as v. early stages in fabric improvement and heating sugg'ns re a cold garden room, currently heated with resistance elec.

    I had typed that the links I had posted seemed silent on CoP, but then:

    Stop Press, the aircondirect one says:

    3.52 kW Cooling, 3.46 kW

    Heating Power consumption (W) 1.3 kW(cooling), 1.15 kW(heating)

    Running Current: 5.65 Amps(cooling), 5.0 Amps(heating)

    ...suggesting a CoP of 3...(?)

    Will look at your sugg'n re 'indoor' units, RobL. Thanks.


    It blows some air outside, so fresh cold outside air will infiltrate in to replace it. The CoP probably doesn't include the energy that will be needed to heat up that infiltrating air. If you add that in, the CoP will be about 1.0-2.0 depending how cold the outside air is.

    Direct electric heating is no longer the no-no it once was, the grid has decarbonised and will continue to do so. The question is whether the money and resources invested in the device, will save enough electricity consumption to be worthwhile?
    Thanks Will,

    Probably back to a mini split then...

    Will chase some prices for the 'all indoor' units RobL linked to, but I'm always nervous when there's no prices listed!
    • CommentAuthorCX23882
    • CommentTimeJan 17th 2022
    I've been using one (Zanussi ZPAC11001) for the past few days, due to failure of my gas central heating.

    It worked surprisingly well - it has no trouble warming a 3m x 3m room within a few minutes, and didn't do bad at keeping adjacent rooms at a comfortable temperature. Obviously makes an absolute racket, due to the compressor being in the room with you, but it gets the room warmer faster than an oil-filled electric heater (similar power consumption from the wall - between 1.2kW and 1.5kW). Like all UK portables, it's a single hose unit, with the cold air exiting through a window and make-up air coming from other rooms.

    The biggest issue I ran into is how often the tank needs to be emptied. When in cooling mode in the summer, it will run for days without needing emptying. In heating mode, I was emptying 1L of water out of it hourly! This was in spite of indoor humidity being around 45% at 18 degC.
    Thanks CX23882

    It's been a good learning experience but I think the diversion via portables takes me back to the 'proper' split unit idea for this particular client and their cold garden room. As I understand it there'll be significantly lower noise (because, as you say, you haven't get the unit in the room with you) and far better CoP. All we need is an installer who will install a cheap unit not too expensively!

    Thanks again to everyone.


    • CommentAuthorowlman
    • CommentTimeJan 18th 2022 edited
    • CommentAuthorLF
    • CommentTimeFeb 5th 2022
    Hi all note decision made for this case.
    I actually ran a portable for say 4 years as a bathroom heater and extraction unit from back in 2010. Worked ok.
    My experience seems to echo comments here.
    Located unit in old airing cupboard to contain noise and had hor air piped under bath into bathroom to blow on laundry. Cold air direct to outside via a big home made plastic connector to 6 inch vent in wall short.
    1) fan broke twice on unit on hot side, only about 40 C heat. Plastic cracks. Metal fan but restricted by casing on air con unit and cupboard space. Hacked controls into a sandwich boxs under the sink unit for controlling off and on via its remote.
    2)bathroom lovely and warm when running good for bathing little ones. I never got round to piping excess heat to downstairs.
    3) a lot of air flow is a lot of dedusting on filter mats
    4) plumbed in condensate
    5)I think cop 2.5 ish
    6);6 inch ducting for 2KW out séems to be what I remember. Bulky stuff
    7). Good for air changes on house overall too whilst recovering heat

    Could not see a root cause on fan failure and gave up. I did size ducts correctly. Metal fan needed? We still had mould issue on tiles.

    Used a dessicant air con unit now for laundry. Much smaller and lighter and waste heat also warms bathroom room. No refridgeration cop benefit though. Likely to use a small refridgerant dehumidifier when this fails.

    Mould issue sorted with bathroom rebuild, warmer walls and shower bath in enclosure where wet air is directly vented via extractor to outside.
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