Radiator union change from 3/4 to 1/2 puzzle

[GrogSym]

Well...
I have some 'traditional' style trv valves on my rads which I fitted last year. The rads had a 3/4 inch inlet, and it took me a long time to find valves that had a 3/4 inch fitting (there are 3 linked rads on a bay window, hence why they were 3/4). It's a union joint between the rad tail and the valve body.

I'm now changing the rads as part of a wider project to lower my boiler output, and as you'll know, the new rads have a 1/2 inch input.

So, and I think I know the answer to this, can you think of any way that I could use my current valves with the new rads?

 

[GrogSym]

Pic attached

 

[oldbuffer]

1. Take the tails out of the old radiators and use them in the new ones.
2. Radiators are almost invariably tapped 1/2" BSP female, so the old ones should fit the new radiators.
3. If you are unlucky and the old tails are 3/4" BSP you will need to change the valves, unless you can find some 1/2" BSP union tails.
4. Not quite sure why you need to change radiators to alter boiler output. Many boilers can be range rated and / or modulate down sufficiently to allow for lower output.

 

[GrogSym]

Thanks! I've had the tails out and they are indeed 3/4 inch - rare, but true.
I'm swapping older panel radiators with type 22s sized to allow me to run the boiler at 50 degrees, will help fight the cost of living crisis!
I'll have a look for 1/2 union tails, but fear they still wouldn't mate with the valves. I suppose I could always return them if they didn't!

 

[Deleted member 267285]

They look similar to these, which appear to be 3/4” x 1/5” tails

 

[GrogSym]

Thanks, I've bought some tails on eBay, hoping I'll have a bit luck...

 

[winston1]

I'm swapping older panel radiators with type 22s sized to allow me to run the boiler at 50 degrees, will help fight the cost of living crisis!
I

Don’t understand that. If you lower the boiler temperature you lower it’s output and you will be cold. You cannot get something for nothing.

 

[oldbuffer]

Lowering the boiler temperature while increasing radiator area will:
1. Enable the boiler to operate in condensing mode for more of the time. This will marginally improve the efficiency.
2. Make the whole system more in line with the lower temperature / larger surface area requirements for heat pumps.

 

[winston1]

1. Can’t answer that, do not know enough about condensing boilers (if he has one).
2. Heat pumps will not help the cost of living crisis. Although heat pumps are cheaper than conventional electric heating by a factor of around 3 they are still dearer than gas which is a quarter the price of electricity. Not to mention the cost or replacing a boiler with a heat pump.

 

[Madrab]

If I understand you correctly, if the radiator tails, the male section that screws into the radiator tapping is 3/4" and not normal 1/2" and you want to keep the valves that you have. For them to fit a modern rad you will need reducing bushes, that will step down the 3/4" male end on the tail to 1/2" to fit the radiator tapping.

As suggested, if you want to run the system @ 50deg and still warm the spaces correctly, then you will need to increase the size of the radiators significantly. Either that or you upgrade to UFH, which would run cooler as standard.

 

[Johntheo5]

Lowering the boiler temperature while increasing radiator area will:
1. Enable the boiler to operate in condensing mode for more of the time. This will marginally improve the efficiency.
2. Make the whole system more in line with the lower temperature / larger surface area requirements for heat pumps.

Normally rads are 50deg rated which is the mean rad temp minus the required room temp (generally accepted as 20C), so if you run the boiler at 50C with a return of 40C, then you will have a 25deg rad, (50+40)/2 minus 20, with a output of, (25/50)^1.3, 40.6% of its 50deg rating so rads should be oversized by a factor of, 100/40.6, 2.46, say X2.5 which should be OK with a heat pump in mind even though a factor of X3.0 would be even better to obtain the maximum heat pump efficiency (COP) with lower water temperatures.

 

[GrogSym]

Interesting that a thread on valves stimulates as much convo on running boilers cooler - I like it. I've done a comprehensive heat loss calc for every room, then come up with a realistic plan for insulation and re ran the calls. I've just finished insulating under my living room floor with wood fibre, and upgraded the rads in there. Going to do the rest of the rads before winter comes in the hope to reduce bills - it's a big old house. I'll then have a house that will be future ready for when I am ready to take the plunge, thankfully I have a 3 phase supply as it would take a lot of leccy!

 

[GrogSym]

Oh, I've also created a radiator size calculator if you know how many watts you need, you can change the flow temps etc and it sizes the rads. Will post on a different thread some day!