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Hydronic plinth heaters and ASHPs

 
Wood Burners, Biomass, Small Scale, Biofuels & Other Heating Alternatives
Last Post by benson 1 year ago
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 benson
(@benson)
Reputable Member Member
Joined: 3 years ago
Posts: 301
Topic starter 03/05/2025 4:44 pm   [#2292]

Hi all,

Wondering if anyone had experience of the above, combined with ASHPs? 

Redoing our kitchen at the moment. UFH is a no go. Looking at the plinth heaters some of the larger ones will just about meet the heat loss of my kitchen (pretty much dead on in fact), and will involve significantly less plumbing work than what I was looking at doing with having to move/change the radiator to accommodate the plans with the units. 

Thanks

 



   
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 Judith
(@judith)
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Joined: 3 years ago
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03/05/2025 6:18 pm  

We have one and it’s a bit undersized since it was the original on the hotter water gas system. But nevertheless we only needed to flick it on for a few hours this last winter.

The only subtlety is it has to be on the summer setting (Myson 1kW) since on the winter setting the fan switches off when the flow temperature is below a (can’t remember) value.

It works very well because being fan driven the wattage reduction with flow temperature is not as steep as a radiator.


2kW + Growatt & 4kW +Sunnyboy PV on south-facing roof Solar thermal. 9.5kWh Givenergy battery with AC3. MVHR. Vaillant 7kW ASHP (very pleased with SCOP >4) open system operating on WC


   
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 benson
(@benson)
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Topic starter 03/05/2025 7:10 pm  

@judith thanks. Good to know yours is working well. There do appear to be some that cater for lower flow temps, as in fan won't switch off on certain models, which is good. The only thing I can't quite get my head around is how they would be balanced as a normal radiator would, with lockshields, and whether this would lead to inefficiencies. I could get a radiator into the revised plans it would involve taking a fair few floorboards up, and I think extending the tees to the radiator around 3 metres as well to get it over the other side of the room.



   
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JamesPa
 JamesPa
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04/05/2025 1:31 am  

Posted by: @benson
↑

The only thing I can't quite get my head around is how they would be balanced as a normal radiator would, with lockshields, and whether this would lead to inefficiencies

I have a mitsubishi wall mounted fancoil which is I think essentially the same construction as a plinth heater.  No hydronic balancing needed, it modulates the fan speed to adjust the temperature.  Great piece of kit except that it turns off when the water temp goes below 30C and this figure is not adjustable, which could cause problems at the ends of the season.  For me it's just about ok but I can see it may be problematic in some cases.


4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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 benson
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Topic starter 04/05/2025 11:11 am  

@jamespa we should be ok as the model I'm looking at has the same cut off (30) and our min flow temp is 35.

Would the reduced volume in the system be a problem do you think? Our current kitchen radiator is a fair size albeit we do have 17 radiators in total so it is a relatively small proportion of the total.



   
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JamesPa
 JamesPa
(@jamespa)
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Posts: 5561
04/05/2025 1:01 pm  

Posted by: @benson
↑

@jamespa we should be ok as the model I'm looking at has the same cut off (30) and our min flow temp is 35.

Would the reduced volume in the system be a problem do you think? Our current kitchen radiator is a fair size albeit we do have 17 radiators in total so it is a relatively small proportion of the total.

Unless your defrost is already marginal I can't see it making a material difference but of course you could, if you were concerned, do the calculation or add a volumiser when the system is drained.

 


4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.


   
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 benson
(@benson)
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Topic starter 04/05/2025 1:50 pm  

Thanks. I suspected I was overthinking that part. 👍



   
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Mars
 Mars
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05/05/2025 10:44 pm  

@judith off the topic, but just saw in your signature that you MVHR. Was that a retrofit install?


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Mars
 Mars
(@editor)
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05/05/2025 10:50 pm  

@benson will you be proceeding with the plinth heaters and which brand(s) are you considering?


🔥 Britain’s Heat Pump Shitshow
How Installing a Heating System Became a National Nervous Breakdown
Free UK shipping.
📗 Heat Pumps Explained
A Jargon-Free Guide for Homeowners
Rewritten and updated for 2027
📘 From Zero to Heat Pump Hero
🛠️ Bodge Buster
New to heat pumps?
Take the Heat Pump Fundamentals course and use INTRO50 at checkout for 50% off.


   
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 benson
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Topic starter 06/05/2025 7:59 am  

@editor yes I think so. It will be a while until I get around to fitting it but just need to plan for pipework etc hence researching early. It was the Thermix ones I was looking at which are specifically designed for ASHPs and lower flow temps.



   
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