Ufh vs replacing my radiators?

waqasahmed

So

The radiators in this house are likely over 20 years old

Given that, I'm not sure whether it'd be worth getting new radiators, or getting ufh. I'm going to have to pay up anyway

My heating is via gas currently too

Rodders53

No obvious reason the radiators will not function adequately for another 10-20 years.

Electric UFH will be expensive to run.  Wet UFH, to do properly, requires digging up floors, or other disruptive and expensive work.

Screwdriva

Disruptive and expensive, yes. But so much more comfortable, tidy and more efficient thanks to the lower flow temperature. Also a near must have for a heat pump. 

waqasahmed

Rodders53 said:

No obvious reason the radiators will not function adequately for another 10-20 years.

Electric UFH will be expensive to run.  Wet UFH, to do properly, requires digging up floors, or other disruptive and expensive work.

Is wet UFH basically powered by water coming from the combi boiler? 

Could you use the same UFH later for heat pumps? Also I thought you should replace radiators every 15-20 years? 

ABrass

waqasahmed said:

Rodders53 said:

No obvious reason the radiators will not function adequately for another 10-20 years.

Electric UFH will be expensive to run.  Wet UFH, to do properly, requires digging up floors, or other disruptive and expensive work.

Is wet UFH basically powered by water coming from the combi boiler? 

Could you use the same UFH later for heat pumps? Also I thought you should replace radiators every 15-20 years? 

Rubbish, radiators will last ages. If you're not seeing issues with them then there's no point replacing them 

You can use a combi boiler with UFH and you can swap them over later.

UFH is lovely, but unless you're doing the entire floor and have very good insulation (roof, walls and especially floor) then it is a bad idea.

Soot2006

I replaced my old rads but only because they were single-panel or a bit smaller than I'd like. I've supersized everything. Did upstairs last year; the difference was amazing - quicker more efficient heating. Am doing downstairs now too.

Rodders53

waqasahmed said:

1) Is wet UFH basically powered by water coming from the combi boiler? 

2) Could you use the same UFH later for heat pumps?

3) Also I thought you should replace radiators every 15-20 years? 

1)  Yes.  The CH hot water that goes through radiators most often, not the Direct HW.

2)  Yes.  But need to be oversized / designed now for the expected lower flow temperature of HP.  Sometimes larger bore pipework may be needed to keep water flow rate down.

3)  Who told you that utter rubbish?  As long as they look OK and the inhibitor in the CH water is correct strength they will last ages.   Even moreso on modern unvented CH systems.

NB Wet UFH really needs designing in from the building construction... and it was (allegedly) in our current oil-fired home. Plus lots of insulation and draught-proofing.  UFH is not all it's cracked up to be, we find.  (Suspect a relatively poor design/installation).

You can get alternative 'floor overlay' systems and they can work OK, but need doors altering and you lose some room height for the insulation and pipework.

You have a lot of reading up to do if considering such a retrofit!

waqasahmed

Rodders53 said:

No obvious reason the radiators will not function adequately for another 10-20 years.

Electric UFH will be expensive to run.  Wet UFH, to do properly, requires digging up floors, or other disruptive and expensive work.

Fair enough. In that case, I'll just leave them be if it means I don't *have* to change them out. I'd hope they're good enough for a heat pump 

Screwdriva

waqasahmed said:

Rodders53 said:

No obvious reason the radiators will not function adeq

Sorry to say that a heat pump will run efficiently only on oversized T22 or T23 radiators (Double fin/ double panel or Triple fin/ triple panel).

Anything else will not output the heat required at a low enough flow temperature (45 degrees) to enable a high enough SCOP in excess of 4.

This is why heat pumps work well with wet UFH - massive surface area & much lower flow temperatures!

ABrass

Screwdriva said:

waqasahmed said:

Rodders53 said:

No obvious reason the radiators will not function adeq

Sorry to say that a heat pump will run efficiently only on oversized T22 or T23 radiators (Double fin/ double panel or Triple fin/ triple panel).

Anything else will not output the heat required at a low enough flow temperature (45 degrees) to enable a high enough SCOP in excess of 4.

This is why heat pumps work well with wet UFH - massive surface area & much lower flow temperatures!

That's a gross oversimplification. Radiators need to output the appropriate amount into the room given the heating needs of the room.

In a passivhaus then a tiny radiator will work. In a 1930s build with solid walls and draughts no realistic radiator is going to manage with sensible heat pump levels.

And since heat pumps are only ever suitable for very well insulated houses then radiators can be effective, if they're old enough.

Screwdriva

ABrass said:

That's a gross oversimplification. Radiators need to output the appropriate amount into the room given the heating needs of the room.

In a passivhaus then a tiny radiator will work. In a 1930s build with solid walls and draughts no realistic radiator is going to manage with sensible heat pump levels.

And since heat pumps are only ever suitable for very well insulated houses then radiators can be effective, if they're old enough.

Don't mean to disagree but there is a difference between "working" and maximizing SCOP. 

If you want to maximize SCOP (> 4) with a heat pump, the larger the emitter, the lower your flow temperature (think well below 45 degrees ideally).

Naturally, a heat pump won't save anyone money in a poorly insulated, drafty pre- 1970s house without serious insulation retrofitting. But a general rule of thumb really is maximizing the emitters surface area.