Octopus have carried a heat loss survey and as a result, I have upgraded 3 radiators. In my kitchen I have a plinth heater that runs off the central heating circuit. Only used on really cold days but Octopus have said I need to remove it and replace with an electric one. I appreciate that the flow temperature will be lower 45 - 50° on cold days but it should still work?
It is to do with MCS and the BUS grant.
Basically, if an area is heated by the heat pump it has to be able to reach the required room temperature.
If it can’t, and you still want the grant, then the radiator needs to be removed and the area included as unheated.
But you already have radiators so the problem will be that the plinth heaters are connected to the heating and will be ineffective and I would assume messes with the MCS calculation and the grant approval process.
Let them remove the plinth heaters, and then put them back when they are gone.
That is what I did in a similar situation.
The surveyor should have explained this but maybe didn’t 
We have two plinth heaters.
Ours don’t cut in till 42°C (if I remember correctly) however I’ve connected them to smart plugs and put them on the always on mode so when the sockets are on they’re on.
I then have an automation to switch them on at lower flow temps, one lower than the other. The automation only triggers them when heat pump is doing space heating not DHW. I also have it not operate at night as they are a bit noisy.
Thanks, brilliant idea to use a thermostat to turn the plinth heater on and off.
This is absurd. The OP has to replace ~300% efficient heat pump-driven heating with 100% efficient resistive heating to get the grant? Nuts!
No, the OP doesn’t. Octopus may have suggested replacing with an electric version, I doubt it is compulsory!
My kitchen had a radiator that wasn’t big enough/not enough output and there was no suitable replacement for the available space.
It had to be removed to get the grant, but I just put it back later.
It did no harm being there but MCS rules and, therefore, the grant, required removal.
I found these tables. At 45° my existing SS3 “non heat pump” plinth heater has an output of 400w / 700w (low /boost) whereas the recommended replacement for heat pumps gives 490w/583w. They look pretty similar to me. maybe the fan switches on at a lower temperature but I couldn’t find any data to show the “heat pump” model runs at below at 45°
The heat output at lower flow temperatures will be considerably lower.
They also quote heat outputs at a flow rate of 340l per hour which is only 5.7l per minute, much lower than most heat pumps run at.
How does the boost work, a fan?
Yes there is a 3 way switch “boost-off-low”. On the low setting the air output is like a breeze. I think that Andrew has the answer. If the unit is designed to kick in at 42° then most of the time the unit will not switch on. However, extrapolating the data in the chart; at 40° there should still be 300w on the low setting. But this is less than half what is in the heat loss calculation. Having upgraded all the other radiators, I’ve been running my gas boiler at 45° to “mimic” a heat pump. The rest of the house gets really warm but the kitchen is still chilly as the plinth heater only switches on for a few minutes when set to boost.
Which of these is alleged to be the “heat pump” model? The Smiths ones come on at 38°C.
Sorry, I posted the data sheet for the wrong model. The “heat pump” plinth heaters switch on at 30° but the data sheet only gives output down to 40° but I extrapolated about 750w at 35° so this looks like a viable option.
https://kitchenheaters.co.uk/product-category/heat-pumps/
Hello, did you fit this and find it worked? We have a plinth heater in our utility room and have found it doesn’t come on at all with the heat pump. We are considering replacing it with a ‘heat pump compatible’ plinth heater, but have been told it still might not heat the space. Thanks
I didn’t go ahead with the heat pump install. I spent too long trying to get information about Octopus’s proposed system from them. Eventually, I discovered that I would have to replace my Aqualisa shower pump (£500) for a non vented model and knock down a garden wall for the external unit.
That’s a shame, thanks for responding though
There are two different considerations here, which it might be worth separating out.
Firstly, there’s the controller for the fan in your plinth heater, which is measuring the heating flow temperature as a crude way to tell if the heating is on or not. Your heat pump will be running with a flow temperature much lower than a boiler, so the plinth heater never considers the heating to be ‘on’ - and so never runs its fan. This is essentially an electrical switching issue; others posting earlier in this thread have re-wired their plinth heaters to smart plugs or thermostats to control when the fan runs, rather than relying on the heater’s controller detecting a high flow temperature.
(Fancoil units face the same issue - they basically work the same as plinth heaters - so if you search the forums for “fancoil” you’ll find some other threads that discuss this question.)
Secondly, the heat exchanger in your plinth heater will be sized to provide the desired heat output when fed with high-temperature water from a boiler. Its heat output will be much lower when fed with less-high-temperature water from a heat pump. You may find that even with the fan running there’s not enough heat output - but that depends on how you use your utility room, whereabouts it is in the house and how much heating it gets from other rooms or appliances.
In principle, a ‘heat pump compatible’ plinth heater should address both aspects - as long as it is sized correctly for the heat loss from the room.
Was anything said about this heater when (or before) you had the heat pump installed?