T50 on new install?

[siricosm]

I am about to replace my radiators (and piping) and doing the heat loss calculations. I am wondering if the T50 rating on radiators is still reasonable. Wouldn't T40 be more efficient with today's boilers, or would the difference be hardly noticeably?

I guess T40 would also be at the upper limit of what you could use with a heat pump, which could be an issue if(when?) the government starts to apply pressure to get rid of gas boilers.

What would you use in your own house, if installing a new system from scratch? I am not interested in underfloor heating.

 

[SimonG]

I would always want slightly oversized rads. Controlled on the trv. Easier to turn down if too warm but nowhere to go if too cold.

 

[ShaunCorbs]

If you have the space for the size increase why not

 

[Knappers]

Keep an eye on total volume and expansion requirement

 

[siricosm]

Keep an eye on total volume and expansion requirement

I am planning on using cast iron rads and a thermal store, so the expansion is going to be way more than the vessel in a combi. This is yet another part I don't need.

Surprisingly, regular boilers are even more expensive than system boilers.

Boilers are like bikinis, the less you get, the more you pay.

 

[ShaunCorbs]

Things have moved where 15 years ago heat only boiler was standard ish now not many are getting installed compared to combis

 

[siricosm]

I am planning on using cast iron rads, which are not cheap. So at T40 I would need 1.6x the wattage. For a proper heat pump setup say at T30, one would need 2.4x. So it is hard to know where the sweet spot is.

 

[Knappers]

I am planning on using cast iron rads, which are not cheap. So at T40 I would need 1.6x the wattage. For a proper heat pump setup say at T30, one would need 2.4x. So it is hard to know where the sweet spot is.

Would have 1.6x, would need 2.4x?

 

[siricosm]

As I understand it, if I calculate rad sized based on T50 rads (70C flow), I would need to multiply the wattage I need by 1.6 to have a 60C flow (T40), or by 2.4 to have a 50C flow (T30).

 

[Knappers]

And by wattage needed you mean equivalent output of rad at T50?

 

[siricosm]

Yes. At T40 the rads would need to be 1.6 times bigger, or 2.4 times bigger at T30. (I think).

 

[Knappers]

More than 1.6 seems excessive practically especially with cast rads.
You'd probably have the only cast iron heat pump system in the country!

 

[siricosm]

You'd probably have the only cast iron heat pump system in the country!

Haha, that could be true, but I really like them, I think they look so much better than the modern ones.

 

[Knappers]

Regarding efficiency.
If you can keep the return temp below dewpoint (52°C i believe) then in theory you'll always be condensing so more efficient.
How likely is it that you'd move to a heatpump in future?
If very likely, I'd look at building in redundancy elsewhere (perimeter heating, ventilation etc)
Have you got another more detailed thread on the project?

 

[siricosm]

Regarding efficiency.
If you can keep the return temp below dewpoint (52°C i believe) then in theory you'll always be condensing so more efficient.
How likely is it that you'd move to a heatpump in future?
If very likely, I'd look at building in redundancy elsewhere (perimeter heating, ventilation etc)
Have you got another more detailed thread on the project?

So for max efficiency, T40 (60C flow) is probably good enough most of the time.

I am redoing the heating in my house in copper pipe with cast iron rads, and then I am going to lay hardwood floors, so I am hoping the system will last until I croak. However before that happens (the croaking part), I am worried that the government is going to ban gas boilers, as they are already talking about it for new builds. And you know how this goes, first it is new builds, and then a few years later people have to do it when their boiler dies. So probably not so likely for the heatpump.

I did have a couple threads about aspects of the system I plan to install, but it was mostly about thermal stores (sealed), and the pros/cons compared to unvented systems.

 

[Knappers]

Yea 60 is a good design temp.
Gas boilers won't get banned for decades and by the time they do heatpumps may not even be a thing.
I've done some work for these guys, down the road from me, a bit special and probably silly money.

Home - Beaumont Cast Iron Radiators

At Beaumont, we have been manufacturing cast iron radiators in our own foundry for many years, gaining a solid award-winning reputation for excellent quality

www.beaumontcastiron.com

 

[siricosm]

My favorite are these (our house is 1930s):
Deco Cast Iron Radiator - https://www.tradscastironradiators.co.uk/radiators/cast-iron-radiators/deco/

but I can't afford them, nor the ones in my profile pic. I was originally going to scrounge around for used ones, but then I found these ones which are pretty reasonable:
Traditional Victorian 4 Column 760mm Cast Iron Radiator - https://www.castironradiatorcentre.co.uk/products.asp?code=CDC-760&name=traditional-victorian-4-column-760mm-cast-iron-radiator

 

[siricosm]

Have you got another more detailed thread on the project?

Here you go, I found it:

Please criticize my plan - UK Plumbers Forums | Plumbing Advice; Plumbers Talk Forum

I am new to the UK and just bought a house in Norwich. It has a vented cylinder and vented CH that is suffering from pretty severe corrosion, some of the rads are rusted through, so I would like to replace it with a sealed system. The rads are all plumbed in 10mm, so I would like to replace that...

www.plumbersforums.net

I guess a lot of folks don't like thermal stores, so it a bit devolved into a discussion of pro/cons with unvented. The plan is to ditch the house thermostat, and have the rads controlled entirely by TRVs. This design should also lower the return temperature a bit on all but the coldests days.

If you have any comments on that thread, or any tips or advice, please feel free to post them there. I am about 1/2 way through the install.

 

[Harvest Fields]

Things have moved where 15 years ago heat only boiler was standard ish now not many are getting installed compared to combis

Tell me about it. I’m tired of seeing combi’s in large 4 bed double bathroom houses.

 

[Knappers]

I've had a look, wouldn't a gledhill boilermate do the job?
I don't love it in principle as I dont think the boiler would be as efficient as id like, that would be overcome by having multiple heat sources (back boiler, solar etc) which is where a thermal store would excel domestically.
Just off the top of my head I'd look at separating heat and hw, something like thermal store temp controlled by weather compensator and HW straight off combi.
Wire solar panel to immersion and I'm there!