I saw you mentioned the Stelrad radiators previously and did some research into them and is definitely the ones I’m going to use to replace the old radiators in my house. I looked at k2 ill need to check out the k3 (what is the difference) I have also looked at using a small fan at the bottom of the radiators which allows the room to heat up quicker and potentially reduce heating costs 

From what I've been able to establish, the K3s chuck out a lot more heat than the K2, and they are (apparently) designed for low flow temperatures, so should be idea for ASHP systems.

As for the fans, @crashoverride, told me about Speed Comfort a while ago: https://speedcomfort.co.uk  

They certainly look great, but they are very expensive (possibly prohibitively so), given that they're just a series of CPU fans. So what @crashoverrride did was make his own. I'll ask him whether he's interested in writing an article on how he did it.  

K2 and K3 are essentially the same, but with 2 and 3 panels/sets of fins.  A Stelrad K2 1000x600 gives 1732W, a K3 2389W.  These at 'standard' temps but OK for comparison. So 35-40% more output for a given size.  

My quote assumed K2s but I'm going to ask for a combination.  The K3s are near twice the price so I will have to be selective. 

@kev-m, fully agree. Most of our K2s have been more than adequate, but we're going to upgrade to K3s in rooms that we know haven't been able to come to temperature and they need more heat output. The K3s weigh an absolute tonne. The 700x1000mm weighs over 60kgs.

Hi Mars,

I was surprised to read that you are replacing your radiators. If my memory serves me well, when we discussed your problems some time ago, you were measuring a temp of 23C on the radiator, which would indicate to me that the warm water is not getting to the radiator in the first place.

If the radiator is heating up but cannot get the room up to temp, then that would indicate that the radiator is too small.

Even if you are getting the radiators supplied and installed for free, it would still not solve your problem if the water is not flowing through the radiators. Have you checked for stuck valves or blockages?

Posted by: @editor

They certainly look great, but they are very expensive (possibly prohibitively so), given that they're just a series of CPU fans. So what @crashoverrride did was make his own. I'll ask him whether he's interested in writing an article on how he did it.  

hmm interesting and as I used to have my own IT company I have about a zillion (maybe a gazillion) CPU fans so maybe I can rig something up myself, its the temp controller and its ability to switch them on off that is that little extra bit of zing that you need to balance the heat 

@derek-m, you are spot on. The radiators is just one of the changes as they are undersized for the rooms they’re in.

As part of a lengthy investigation with a lot of testing and analysis by the manufacturers, it was determined the flow to the north end of the house is not good enough, so a bigger pump will be fitted to deliver more pressure to engineer out a potential reduction in pipe bore. 

Water delivery to rads in the south end of the house was 45C, but just 39/40C at the north end.

@boblochinver, that’s exactly right. It’s the temperature control to turn the fans on and off that’s essential so that they don’t burn out. I suppose some soundproof casing would also help to reduce the high pitched noise CPU fans used to make. Don’t know if they still do.

We've been in touch with Stelrad and they have provided us with this promo code that you can use on the Stelrad website to get a 10% discount on their Vita & Softline Compact K3 radiators: MyHomeFarm10% – offer ends on August 10, 2021.

Ohhh thanks

@mikefitz, welcome to the forums. You looking to get some new rads?