Andy T Posted December 4, 2023 Share Posted December 4, 2023 We’re looking for some advice on size of air source heat pump to install if anyone can help please. We have a detached chalet style bungalow, with solid (concrete) floors and with an underfloor wet heating system, currently run on Kerosene oil. The property was built in 2000 and as far as we’re aware has standard type insultation in the walls and loft (we can’t ascertain exactly what we have) and we’ve recently installed double glazing. We’ve done quite a lot of homework and had two companies round to look at our house and quote and had a heat loss survey carried out, demonstrating a total heat loss of 6,688E (43 w/m2). The house is approximately 160m2 . One company recommended a Valliant 7kw Thermo Plus heat pump. The other company (prior to seeing the hot loss report) recommended a Grants 13kW R32 heat pump. On sight of the heat loss report, the second company recommended a Grants 10kw R32 heat pump. We see buying a larger heat pump does not cost much more, but are concerned if we install larger than needed then this may cost more to run and/or not run efficiently. Any help or advice would be really appreciated. Our boiler will probably not last much longer as it’s on its last legs so are keen to get on with this project. Link to comment Share on other sites More sharing options...
SteamyTea Posted December 4, 2023 Share Posted December 4, 2023 Do you know how many litres of kerosene you use each day? Know that, and the local weather, you can get a good idea what size you need. Is your hot water stored in a cylinder? What size oil burner do you currently have? 1 Link to comment Share on other sites More sharing options...
S2D2 Posted December 4, 2023 Share Posted December 4, 2023 Go for the Arotherm plus, correctly sized and a very quiet, efficient unit. Without knowing more we can't say if the heat loss calculation is accurate, but the true value is likely to be lower rather than higher so the 10kW unit is excessive and likely to cause short cycling, lowering efficiency. Link to comment Share on other sites More sharing options...
Andy T Posted December 7, 2023 Author Share Posted December 7, 2023 Thank you so much for both replies. I think we've decided to get another heat loss report just to make sure. Link to comment Share on other sites More sharing options...
Tom Posted December 7, 2023 Share Posted December 7, 2023 Is it going to do your hot water too? 1 Link to comment Share on other sites More sharing options...
Andy T Posted December 10, 2023 Author Share Posted December 10, 2023 Yes Tom, it will be doing the hot water too. Link to comment Share on other sites More sharing options...
JohnMo Posted December 10, 2023 Share Posted December 10, 2023 On 04/12/2023 at 11:06, Andy T said: We’re looking for some advice on size of air source heat pump to install if anyone can help please. We have a detached chalet style bungalow, with solid (concrete) floors and with an underfloor wet heating system, currently run on Kerosene oil. The property was built in 2000 and as far as we’re aware has standard type insultation in the walls and loft (we can’t ascertain exactly what we have) and we’ve recently installed double glazing. We’ve done quite a lot of homework and had two companies round to look at our house and quote and had a heat loss survey carried out, demonstrating a total heat loss of 6,688E (43 w/m2). The house is approximately 160m2 . One company recommended a Valliant 7kw Thermo Plus heat pump. The other company (prior to seeing the hot loss report) recommended a Grants 13kW R32 heat pump. On sight of the heat loss report, the second company recommended a Grants 10kw R32 heat pump. We see buying a larger heat pump does not cost much more, but are concerned if we install larger than needed then this may cost more to run and/or not run efficiently. Any help or advice would be really appreciated. Our boiler will probably not last much longer as it’s on its last legs so are keen to get on with this project. Heat pump sizing is simple enough. you need a heat pump that can deliver your required heat in about 22 hours, this leaves 2 hours for DHW heating. Other other thing to look at is output at your flow temp temperature and lowest outside temperature. This where you need to start looking at different datasheets. Some manufacturers quote the best output figure others the minimum, so headline 7kW doesn't mean the same thing, when comparing products. So you looking for around 8kW output at say -3 to -5 A 10kW Grant heat pump at -7, has a rated output of 8.1kW. So is fine, the next size down is 6kW and is too small. A 7kW Vaillant for example is fine until flow temp required at -5 goes above 45, at 50 it will struggle and outside temperatures below -5 would struggle also. 3 Link to comment Share on other sites More sharing options...
Marvin Posted December 10, 2023 Share Posted December 10, 2023 Hi @Andy T Good info from @JohnMo above. We went for a lower cold of -8 Centigrade which is about 4 degrees below the lowest temp recorded here in the the last 20 years. M Link to comment Share on other sites More sharing options...
Andy T Posted December 27, 2023 Author Share Posted December 27, 2023 Many thanks for this JohnMo. That's really helpful and we've gone ahead and ordered the 10W Grants which will be installed mid-February. Many thanks for this re-assurance Thank you also Marvin for confirming. So grateful for all the help from this site Apologies for the late response, but I've only just seen your two posts for some strange reason. 1 Link to comment Share on other sites More sharing options...
Andehh Posted December 27, 2023 Share Posted December 27, 2023 Nice to see someone actually researching and having a think about their ASHP installation! Good choice. Good luck with it Link to comment Share on other sites More sharing options...
Andy T Posted December 28, 2023 Author Share Posted December 28, 2023 Thank you Andehh Link to comment Share on other sites More sharing options...
JohnMo Posted December 28, 2023 Share Posted December 28, 2023 On 27/12/2023 at 13:36, Andy T said: gone ahead and ordered the 10kW Grant Grant heat pumps can now use Homely if this is useful to you. Should optimise the system for you once the installer has left you to it. Link to comment Share on other sites More sharing options...
Andy T Posted January 2 Author Share Posted January 2 That looks really useful - I've just read about it on the Grants site. I'll definitely look into the Homely system and check with our supplier if we can use this with our pump. Thank you. Link to comment Share on other sites More sharing options...
Garald Posted January 2 Share Posted January 2 I've come late to this discussion, but the 10kW model sounds like the right choice: first, it's actual output is lower than the model name (this is a thing with heat pumps in general) and second, plenty of heatpumps now work as efficiently when working at half steam as at full steam, so to speak. (That's the case for the Mitsubishi I have, for instance.) So, leaving oneself a bit of a safety margin makes sense. Link to comment Share on other sites More sharing options...
Andy T Posted January 3 Author Share Posted January 3 Thanks for this Garald. So reassuring to hear we've made a good size choice as I understand it's more complicated than it may initially appear (bigger isn't necessarily better) and was very worried about getting it wrong. Also pleased that people seem to be aware of Grants as Valliant seemed the obvious choice at first. Also, we're advised that Grants are quick to respond if things go wrong so I'm hoping this is the case. Yes, as you say, I was worried about how the pump would cope working at half steam as well as full steam so the plan was hopefully to have a safety margin. Once again thank you, as feeling very reassured and thankful for this site. Link to comment Share on other sites More sharing options...
HughF Posted January 3 Share Posted January 3 (edited) Shame 99% of Grant Aerona system are installed so badly they work terribly…. Unless they’ve refreshed their design the you’ll get a drop in replacement for a boiler, designed to work with standard s plan wiring, at a fixed flow temperature, with on/off controls. Literally every conceivable way a heatpump shouldn’t be installed… Edited January 3 by HughF Link to comment Share on other sites More sharing options...
Beelbeebub Posted January 3 Share Posted January 3 5 hours ago, HughF said: Shame 99% of Grant Aerona system are installed so badly they work terribly…. Unless they’ve refreshed their design the you’ll get a drop in replacement for a boiler, designed to work with standard s plan wiring, at a fixed flow temperature, with on/off controls. Literally every conceivable way a heatpump shouldn’t be installed… Grant provide some basic "retrofit" schemes but they also seem happy for installers to deviate. The Chofu HP thry rebrand as grant actually seems like a really good unit. It has loads of flexibility for setting up how you like it. We have a (gas powered) 130m2 bungalow with wet UFH in a concrete slab (exposed). It's pretty highly insulated but our flow temps are in the low 30's which easily keeps the place at 20-21C even down to below zero. We did have individual zones but found they didn't really work well. So have switched to the entire slab as one zone and adjust the bedrooms to be a bit cooler by tweaking the flow down a bit in those loops. The Chofu/Grant units have pretty powerful inbuilt pumps (10m head for 10kw IIRC) so you might not need a separate heating system pump. This would suggest your place would be a good fit for a very simple scheme with no buffer and no external pump. IIRC grant are fairly relaxed about not needing a big volumiser, certainly no more than the 30l internal one (useful as it can have an immersion back up/booster in) and possibly not needing one at all if you have a big system volume from the UFH. Link to comment Share on other sites More sharing options...
Andy T Posted January 15 Author Share Posted January 15 Thank you very much for this information. I won't pretend, it does all get quite confusing. It's not too late for us to change to a different unit/different make. I'm wondering whether to go ahead with the Grant or perhaps change to another. Alternatively I'm thinking of asking the installer in advance how they intend to install the unit as this seems to be a large part of whether the unit will be efficient or not.... Link to comment Share on other sites More sharing options...
sharpener Posted January 15 Share Posted January 15 With a plain simple underfloor heating system they should be able to install the Grant 10kW to run efficiently. I see it is not the new one with R290 refrigerant which would be a be a shade more efficient, perhaps that is not yet available in the 10kW size. Was a bit puzzled you had to add double glazing to a house built in 2000, I wonder what other corners were cut? What was the result of yr second heat loss calc and what are the flow temps needed in yr UFH to meet the expected worst case losses? What is the outside temp you are designing for? The 7kW Arotherm Plus is a reputable R290 unit and as @JohnMo says, might well be adequate also unless you are on Dunstable Downs or in a similar exposed position. I have recently been on a Homely training seminar and I am not convinced it would be advantageous for a simple setup like yours. It sounds as though you would quickly get to grips with the fine tuning without it. Link to comment Share on other sites More sharing options...
HughF Posted January 15 Share Posted January 15 4 hours ago, sharpener said: With a plain simple underfloor heating system they should be able to install the Grant 10kW to run efficiently. I see it is not the new one with R290 refrigerant which would be a be a shade more efficient, perhaps that is not yet available in the 10kW size. Except, they probably wont... It'll end up as a system with a buffer/header, with another pump on the manifold, mixing down from 50 degrees... Link to comment Share on other sites More sharing options...
sharpener Posted January 15 Share Posted January 15 5 hours ago, Andy T said: I'm thinking of asking the installer in advance how they intend to install the unit as this seems to be a large part of whether the unit will be efficient or not.... 54 minutes ago, HughF said: Except, they probably wont... It'll end up as a system with a buffer/header, with another pump on the manifold, mixing down from 50 degrees... Get them to draw a diagram of the system they propose and explain what all the components are for. Not so you can find out for yourself, but so you can tell if they know themselves. Link to comment Share on other sites More sharing options...
JohnMo Posted January 15 Share Posted January 15 The Grant unit can be installed in two ways a buffer/low loss header configuration, buffer gives hydraulic separation between heat and UFH - you do not want this configuration. The other is a system volumiser - a buffer is installed in the supply piping only. This is ok. Ideally you want, UFH as a single zone, no buffer, no mixer and no additional pumps, just run on weather compensation. Heat pumps have a minimum system volume as long as your system configuration complies no need for a buffer. But installers want to install in buffers Link to comment Share on other sites More sharing options...
PhilT Posted January 15 Share Posted January 15 1 hour ago, JohnMo said: Ideally you want, UFH as a single zone, no buffer, no mixer and no additional pumps, just run on weather compensation. Heat pumps have a minimum system volume as long as your system configuration complies no need for a buffer. So in summary the Grant 10kW R32 model would be ideal because it has a built in (unlike similar offerings) "HE Pump" which would be powerful enough to serve a simple single circuit UFH zone in a 160sqm single floor bungalow, without the need for a secondary circuit/pump/LLH/buffer Link to comment Share on other sites More sharing options...
Beelbeebub Posted January 15 Share Posted January 15 The grant volumiser is pretty small, something like 15l. It also does double duty as a backup heater that can either take over from the HP if there is some sort of problem or supplement it in extreme weather. Link to comment Share on other sites More sharing options...
Beelbeebub Posted January 15 Share Posted January 15 7 hours ago, sharpener said: I see it is not the new one with R290 refrigerant which would be a be a shade more efficient, perhaps that is not yet available in the 10kW size. Have they launched it already? Link to comment Share on other sites More sharing options...
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