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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorGarethC
    • CommentTimeSep 28th 2021
    We started discussing this on another thread, and I undertook some further research, but am drawing a blank.

    My question is, does there exist high output (say 5kW minimum) fan convector radiators? Ones that work at low flow temps (40 to 50 degrees) for use with heat pumps, and that have roughly similar dimensions to large conventional double panel, double convector radiators (so say 1.4-1.6m length, 0.5-0.75m height)?

    If not, why not? I only seem to be able to find quite small units with outputs of up to 3.5kW. I don't understand why ones with greater surface area, and therefore higher output, don't seem to exist. If they did exist, they would surely represent a cheaper and less disruptive emitter option than under floor heating.

    Would greatly appreciate thoughts on this. I'm probably missing something obvious and someone will be along with a link to a 10kW fan convector directly...
    That size range is more common in commercial/public buildings eg


    I felt that convectors that big, were a bit expensive and noisy for domestic use, although well able to get the kWs out at low temperatures.
    • CommentAuthorGarethC
    • CommentTimeSep 29th 2021
    Finally! Thanks Willl. This provides so much of the info I was looking for.

    I've two 1.4m x 0.6m double panel convector radiators in my large Georgian living room. Each is rated at 2.5kW at (I think) 70 degrees C flow temperature.

    I could in principle (ignore my narrow bore pipes for the moment) replace them with two Caspian units of roughly the SAME dimensions (UV EC 150s, 1.5m length). These are each rated as 2.95kW at 40 degrees C flow temperature at -low- fan speed (the quietest, draught-minimising setting).

    Two problems:

    1. These are as ugly as sin, but let's put that aside for the moment.

    2. More importantly, the Noise Rating of 34.7 dB is -probably- still a bit too high. It would be noticeable in a living room. Possibly ok in a hall. Wall air conditioning units achieve 26, which is pretty near silent.

    Three potential solutions:

    These units might not be fully focused on minimising noise, as they're not designed for residential settings. Minor design changes might be all that's needed.

    Or I could raise the flow temp to 45 degrees, at which each unit is rated at 5.2kw. That's twice what I need, so if the radiators allowed it (these don't), a lower fan speed, and therefore noise, would be achievable.

    Or I could use the 1.8m units, rated 3.65kW at 40 degrees, and again have a lower fan speed and noise (again not an available setting with these).

    In summary, these are nearly, but not quite, an appropriate emitter option for a residential heat pump in an old building. Anyone aware of other makes I could check out? Aesthetics and lower fan noise/speed feel like problems that should be solvable.

    Also, am I missing anything? Will, you said these were a bit expensive, but surely it would be less expensive than retrofitting under floor heating, and an order of magnitude less disruptive?
    • CommentAuthorSimonD
    • CommentTimeSep 29th 2021
    Have a look at Jaga - jaga.co.uk - which I'm sure sell a fan assisted convection radiator for heatpump installations. Dynamic boost or something I think it's called.
    • CommentAuthorGarethC
    • CommentTimeSep 29th 2021
    Many thanks Simon, another piece of the jigsaw!

    Their Maxi 2020 range is visually more appealing, and, for example, their 1.4m x 0.74 unit provides 2.3kW at about 40 degrees flow rate with fan assist and the noise rating is 30dB, which is a shake better than the Caspians, although probably not quite good enough for a living room.


    Main problem with these are:

    1. Just one of those units, not including the cost of fan assist, is a cool £1450!
    2. The fan assist is pretty much just bolt on. I'd be amazed if sound insulation, and the boost provided by the fan, were optimal.
    3. They have a bewildering number of options. This must explain the pricing. Each one is probably made to order.
    I figured I could disguise the ugliness with Georgian-style panelling, its only the air vents that need to be unobstructed.

    But 40dB and £1k each is too much, as I would need several. Don't forget the wiring to provide a power spur to each one.

    The A-A heatpump indoor units are both quieter and cheaper, so it must be possible, as you said.
    • CommentAuthorGarethC
    • CommentTimeSep 29th 2021
    This all prompted me to have another look at the Myson offerings, and in some ways they remain the best.


    An iVector MkII iV60x140 has output of 2.2kW at the lowest fan speed, which is nearly enough. The 160cm model manages a healthier 2.6kW. Importantly, the claimed sound pressure is just 21dB, which is much better.

    However, I've a couple of queries:

    1. The sound pressure is rated as a distance of 2.5m. At 1m, which is a more useful distance, sound will be much higher.

    2. The heat outputs are given at a "delta T" of 30 degrees C. I assume this is the difference between flow temp and ambient temperature. If the latter is 20 degrees, the flow temp is 50 degrees, which is a little on the high side, but not terrible.

    The only price I can find online for the 160cm model is £760 (presumably ex VAT), so a little better than the alternatives we've found, but it still feels expensive for a coil of pipe in a box with a fan inside. Probably not entirely fair of me, but it does still seem pricey, even allowing for the control system etc.
    • CommentAuthorGarethC
    • CommentTimeSep 30th 2021
    In case of interest, found a reasonably recent report on the cost of installing different heating systems:


    A few summary statistics:

    Air to water heat pump: 16kW ASHP fully installed including buffer tank and cylinder and heat distribution system (retrofit system with upgraded existing radiators): £ 14,900

    New gas boiler: 24kW combi for combi direct swap by local installer/plumber (including labour and fittings but excluding controls and heat distribution system): £ 2,250

    And therein lies the problem...

    For interesting reference:

    Air to air heat pump: 4 bedroom house (4 x 2 kW for bedroom + 1 x 5 kW for lounge) - large distance between indoor and outdoor units: £ 8,800

    Sigh. Still not cheap, and I know they don't do hot water, but I really think air conditioners should be promoted.
    • CommentTimeSep 30th 2021
    Posted By: GarethCIn case of interest, found a reasonably recent report on the cost of installing different heating systems:


    Thanks for that. It looks very interesting. Now to start digesting it ...
    I just had a quote for an ASHP and radiator replacement that was roughly in line with that figure. 16kW is a big HP, we are looking about 12kW.

    Roughly, the cost broke down as

    Supply and fit radiators was about 20%
    supply of the ASHP and ancillaries was about 30%,
    labour about 30% incl a big electrical subcontract
    Supply and fit new DHW cylinder about 20%*

    We currently have oil (no gas) so need to allow extra cost of removing oil tank + bund and landscaping.

    This isn't an exact comparison with the quoted cost for a gas or oil boiler, as that didn't include radiators and controls, which are due for replacement sooner or later.

    People can get up to £9100 of RHI over 7 years (better be quick), and (probably) the ASHP energy bills will be less if using off-peak electricity than oil.

    So overall the costs are roughly equal, but the ASHP costs are much more up-front. The ASHP work will be more disruptive.

    ISTR that solar PV once used to cost £15k and fell to £4k over a decade, but others will have experience of that.

    *Not yet resolved whether our existing cylinder is adequate
    • CommentAuthorgravelld
    • CommentTimeOct 1st 2021 edited
    Yes, the current price referred to in that document is heavily influenced by the RHI. As such, the cost can only be considered when you also take the RHI into account.

    AFAIK you can get more than £9100, I was quoted around £12.5k (for the RHI). I think it depends on the current heat demand? Although it was capped at one point to about 30MWh/annum (IIRC).
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