@cathoderay in fact I think most of our current radiators are oversized for 70C flow. Most of the house was actually acceptable last winter at 50C flow, it was just the living room where on cold days we could "only" get to 22C temps.

So I'm hopeful that by adding a decent amount of insulation where there was none, that may already be enough and the increase in sized would give us headroom we need.

Posted by: @toodles

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@jamespa i.e ‘We know it is flawed, but we are covering our @rses’. Regards, Toodles.

Precisely that.  The method is based on BS something or other, I forget which, so even MCS can say it's someone else's.

BS something or other is designed for new build where you know what the construction is, not retrofit where you don't, but hey-ho.

In summary MCS covers it's backside by reference to bs something or other, and the installers cover theirs by reference to MCS.  The only loser is the customer.  That of course is perfectly satisfactory from the pov of an industry funded body.

Posted by: @scalextrix

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So I'm hopeful that by adding a decent amount of insulation where there was none, that may already be enough and the increase in sized would give us headroom we need.

If you do this take pictures and get receipts, you may need to get to convince installers it's been done unless the insulation remains visible.

@scalextrix And the chances are you might not have been running your heating ‘24/7’ as you might an ASHP? Regards, Toodles.

@jamespa I have a feeling that there is a play based on groups all basing their requirements on someone else’s requirements - who in turn, based theirs on someone else’s….. Regards, Toodles

Posted by: @scalextrix

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Home most days, set system to heat 6AM - 11PM, main thermostat

But that isn't the best way to run a heat pump. Weather compensation run 24/7 and if you need a very small nighttime setback of a couple of degrees only

Posted by: @scalextrix

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I think most of our current radiators are oversized for 70C flow. Most of the house was actually acceptable last winter at 50C flow, it was just the living room where on cold days we could "only" get to 22C temps.

That sounds promising. Do you still have the heat loss/rad sizing calculations used to select your current rads? If you do, they may add some more info. If not, using your per room current heat loss calculations, you could check a few of the rads to see how they match up. The down-rating for use at lower flow temps (strictly speaking, lower delta t between the mean rad temp and room temp) is pretty straightforward, by applying a 'correction factor' such as those found on this page for Stelrad rads. For example, at a delta t of 30 (eg highish heat pump setting with LWT 52.5, RWT 47.5, mean rad temp 50, room temp 20 degrees), the output of a rad is half (51.3%) what is with a delta t of 50 (rads 70, room 20 degrees), which is the number behind my earlier statement that by and large correctly sized fossil fuel rads will nee to be roughly doubled in size/output to work with a typical heat pump (not high temp heat pumps, which are I believed intended to allow reuse of existing rads, but I strongly suspect you then end up paying more in ongoing bills).

Thus if the correct rad on a fossil fuel system is 1000W, then you will need one rated at 2000W (at delta t 50) for your typical heat pump, which will then put out 1000W (2000 x correction factor of 0.531 = 1062W) at heat pump flow temperatures. If you run you heat pump lower flow temps, you will need even larger rads...

I emphasise all this because I suspect it (not matching the rads to the heat pump) is a common reason for under-performing systems. It's all very well getting the heat pump sizing right (and of course that is not a back of the envelope job either), but if the rads (heat sprinklers) are too small, they won't be able to deliver enough heat, a bit like a garden hose with plenty of water available behind it, but the nozzle on you sprinkler is too small, and it takes forever and a day to get the watering done.

There might be another analogy based on the waterworks of men of a certain age, but I won't go into that one.             

@cathoderay Having had cancer of the prostate a few years back, I appreciate what you are inferring! Toodles.

Posted by: @jamespa

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@ianmk13 

Where are you located?  With this info maybe someone here can provide.a recommendation 

I'm in Milton Keynes.

I have performed my own quite thorough heat loss analysis. taking into account my detailed knowledge of the construction of my unconventional home. I also paid a modest sum for a remote, desk-based report as a 'sanity check'. When calculating my heat loss through windows, I contemplated replacing my old (35 year old) DG units with new argon-filled ones but this didn't give a sufficiently marked improvement to the heat loss.  By far the biggest unknown was the loss due to air change.  I don't consider my home to be draughty, but short of commissioning a pressure test, my estimation of the heat loss is no better than a finger in the air. 

During last November to January, I set my boiler to its lowest setting of 12kW (I didn't notice any modulation of the fan while the burner was on) with no overnight setback and recorded daily gas use, flow and return temperatures, IAT and OAT.  I have a lot of data if I can find a proper ASHP heating engineer who will make use of it. I also have a detailed plan of my existing plumbing which includes pipe gauges but I need to add lengths.

Posted by: @jamespa

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In summary MCS covers it's backside by reference to bs something or other, and the installers cover theirs by reference to MCS.  The only loser is the customer.  That of course is perfectly satisfactory from the pov of an industry funded body.

Exactly the same situation with solar and battery installation. MCS refer to IET regulations for warning labels, among other things.  The IET documents are expensive to procure so installers don't buy them or understand the details, but buy sets of warning labels 'in accordance with IET document something or other' and apply them to the equipment. I assume that this would explain why I now have various warnings relating to lead-acid batteries on my LiFePO4 battery pack. 

@johnmo understand, but I don't have a heat pump yet or weather compensation, all I can do is hard set flow rate to 50C.

If there is a better way to simulate with the things I have please let me know.

Posted by: @cathoderay

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Do you still have the heat loss/rad sizing calculations used to select your current rads?

It was installed 18 years ago, plumber just used his thumb-ruler, not calculations.  Though back then the house had draughts under doors, poor windows/insulation and all these have been upgraded in the last two decades.  Back then we spent £100 per month in gas in winter, for the house to still be cold.

So rads were probably over sized at 70C so the plumber didn't get a call back.

According to the new heat loss survey the hall radiator (almost all internal walls) is 80% oversized (large type 22).

I'm thinking the secret to heat pumps is to try and have all the rad sizes matched to the rooms heat loss and then not use TRVs as much.  Oh and emitter balancing is key as well, our living room is last on the circuit and I think the heat isn't always getting there without the boiler cycling.  Just need some colder weather to rebalance it all.