UFH Flow/Return Pipe Size

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Hi all

My idiot builder who took a year to not complete my extension has run the flow and return pipes to my UFH manifold in 15mm from the feeds to an old rad instead of the usual 22mm from the boiler.

He didn't get as far as buying the 2-zone manifold, so I've got all the gear ready to plumb in. Pump, manifold, 2-port zone valve, wiring centre and actuators. I'll be controlling the 2 loops separately via a Tado thermostat in each room.

Loop 1 is about 15 sq m, pipe length 50m.
Suspended timber floor with 16mm pex-al-pex pipe laid in biscuit screed between joists on top of insulation.

Loop 2 is about 35 sq m, pipe length 100m.
Half solid floor, the rest is same as loop 1, but with big bi-fold doors.

Does anyone know whether the system would run well off the 15mm pipes? I know it would be better to run new 22mm pipes from the boiler, but I'd probably end up calling a plumber in for that, so want to know whether it's essential or not.

I'm tempted to just plumb it all in using the 15mm pipes with reducers for now and see how it goes.

TIA
 
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It would be able to run ok assuming the pump on the primary is big enough for the length of the 15mm run and you can balance the system. You can get well over 10kw from 15mm pipe depending on temperature difference.
I'm no plumber though and best practice would be different if it's a long run of 15mm you might end up with no real flow.
 
It'll work after a fashion but I think you'll be disappointed with the results. It's not so much the size of pipe that's the issue, as the fact it's running off your radiator circuit.

UFH takes much longer to heat up and cool down than radiators, so it usually needs to be turned on earlier, hence the requirement for a separate zone. Having everything running together will inevitably mean that the UFH-heated rooms will lag behind.

Happily though, as you're going over to Tado, there is a second option for you - rather than running new pipes all the way back to the boiler, which is potentially disruptive, you can buy the Tado radiator heads and fit them to every radiator in your house. These will then be able to provide you with the control you need to get over the poor pipework situation, as well as improving the efficiency of the overall system.

You've given us a bit of info about the UFH, but not the critical bit - what was the designed output of the system? Or is there no design and your builder has just slung some pipe into the floor and hoped for the best?
 
Firstly, Homeowners would get so much more value for money AND facilties that are fit for their needs and wants, IF they appointed a heating engineer plumber independently to builder when embarking on property improvement projects, or at the very least, consult directly with the builder's preferred plumber.

I have been (and continue to be) called to hundreds of issues with heating and plumbing post build, when everything has been closed up. It's either rip out and redo or apply sticky plasters to broken arms!

@oursurveysaid you'll need to calculate flow rates through the flow and return to the manifold and also those required for the UFH to determine if supply suits demand.
You'll need run lengths and add on for bends, elbows, 135's etc. Once you have this data, you may be able to call the pump technical dept (or the manifold manu) or, if you bought it all from a UFH supplier, they may be able to help you with the calculations.
If you still have reasonable access to the primaries, it may be prudent to get them changed to 22mm anyway... Better to be looking at it, than for it!
 
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Thanks for your advice, guys. Much appreesh!

It would be able to run ok assuming the pump on the primary is big enough for the length of the 15mm run and you can balance the system. You can get well over 10kw from 15mm pipe depending on temperature difference.
I'm no plumber though and best practice would be different if it's a long run of 15mm you might end up with no real flow.

Thanks @John D v2.0. The 15mm is about 10m from near the boiler to the manifold. It's only a little 2-up 2-down victorian terrace.

It'll work after a fashion but I think you'll be disappointed with the results. It's not so much the size of pipe that's the issue, as the fact it's running off your radiator circuit.

UFH takes much longer to heat up and cool down than radiators, so it usually needs to be turned on earlier, hence the requirement for a separate zone. Having everything running together will inevitably mean that the UFH-heated rooms will lag behind.

Happily though, as you're going over to Tado, there is a second option for you - rather than running new pipes all the way back to the boiler, which is potentially disruptive, you can buy the Tado radiator heads and fit them to every radiator in your house. These will then be able to provide you with the control you need to get over the poor pipework situation, as well as improving the efficiency of the overall system.

You've given us a bit of info about the UFH, but not the critical bit - what was the designed output of the system? Or is there no design and your builder has just slung some pipe into the floor and hoped for the best?

Cheers, @muggles! I already have Tado smart TRVs on my 2 radiators upstairs. There's nothing on the towel rail in the bathroom, which acts as a bypass. That's why I'm not too bothered about zoning everything off in the usual fashion. I'm aware that the 15mm pipes would mean it'll take longer for the floor to heat up, though I don't know how much of an issue that'll be until I try it out.

My builder did mention something about BTU and kW, so I think he spoke to Wunda before buying the pipe and laid it correctly with a denser run of pipe in the extension where there's a lot of glass. The rooms downstairs were previously heated by 3 large and 2 small radiators running from the same 15mm flow and return pipes. I suppose the floor needs more flow though as it doesn't get as hot.

Firstly, Homeowners would get so much more value for money AND facilties that are fit for their needs and wants, IF they appointed a heating engineer plumber independently to builder when embarking on property improvement projects, or at the very least, consult directly with the builder's preferred plumber.

I have been (and continue to be) called to hundreds of issues with heating and plumbing post build, when everything has been closed up. It's either rip out and redo or apply sticky plasters to broken arms!

@oursurveysaid you'll need to calculate flow rates through the flow and return to the manifold and also those required for the UFH to determine if supply suits demand.
You'll need run lengths and add on for bends, elbows, 135's etc. Once you have this data, you may be able to call the pump technical dept (or the manifold manu) or, if you bought it all from a UFH supplier, they may be able to help you with the calculations.
If you still have reasonable access to the primaries, it may be prudent to get them changed to 22mm anyway... Better to be looking at it, than for it!

Thanks, @dilalio. You're right - I thought my builder was consulting with a plumber, or at least the guys at Wunda, but as he left behind a pipe thermostat and a random wireless receiver that's incompatible with my Tado system, I'm not so sure! I'll do the calculations, but will probably just plumb it in with the 15mm pipes as they're already there. I've got nothing to lose, have I? If it's not heating the room up enough, I can have 22mm pipes run from the boiler when I rip the floors up upstairs.

Thanks for your help, guys. I guess there's more to it than just a yes/no answer. Wish me luck!
 

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