Ineffective underfloor heating

[NoelM]

The 2-zone underfloor heating installed by our AWOL contractor isn't really doing the job now that the colder weather is arriving - particularly in one zone where the floor gets tepid (~25 degrees) but never warmer and this doesn't seem to be enough to keep the (glassy) room warm on winter mornings, even with the UFH turned on 24/7.

 

I imagine there could be a bunch of reasons for this that will be bloody expensive to fix (e.g. bad substrate or pipe spacing), and I'm very open to suggestions for things I should be doing.

 

But as a first step I thought I'd rule out something easy to fix by venting the circuits and adjusting the water temperature. And I have some questions on that front.

 

We have isolator valves for flow and return on the _manifold side_ of the pump/mixer, rather than on the boiler side. This differs from examples I've seen online where the plumber makes a point of closing off boiler-side isolator valves AND opening up the mixer before venting the system. In these online examples, water is then still able to circulate around the manifold through the pump and mixer valve, but cannot flow back to the boiler. I can't see how to accomplish that same result with my setup.

 

1. Does having the isolator valves on the manifold side seem like a legitimate design decision or is it a mistake?

 

2. If the design seems ok, should these isolator valves be open or closed when I pump water in to vent the circuits? I guess closing could be safest re keeping reverse flow away from the boiler, but if I close them the water will not be able to circulate like it can in the online examples. Maybe this isn't an issue?

 

3. I've been adjusting the temperature on the mixer valve, but have realized that the collar (circled in green) actually moves. When the valve is open, this collar can actually rotate so that the triangle indicating the limit is in different places, and the min/max limits on the valve end up at different amounts of open/closed! With that in mind, I don't really know where the correct position is for this collar, nor what the correct setting is for MAX. How do I make sure I'm not overheating (or under heating) the circuits when setting to MAX?

 

Thanks in advance for any help you can offer!

 

[ProDave]

You really need a themometer on the flow manifold to check what temperature it is at.  A simple solution is to buy a cheap infra red handheld thermometer and use that.  Only then can you tell if the flow temperature is correct and being regulated properly.

 

What do you mean by "venting the circuits"?    Do you mean flushing water through them to ensure there are no air leaks?  If so shut the red and blue isolating valves, connect a water supply hose to the fitting on the right of the top manifold and a drain hose to the fitting on the right of the bottom manifold and run cold water through each loop in turn until water flows through each with no air bubbles.  You really want to do that one loop at a time, so put the actuators back on (not energised) and remove one at a time to allow water through each loop one at a time.

[JohnMo]

1. No issue with the way setup, you are able to change pump without having to bleed full UFH system.

2. Are you hearing gurgling when UFH is on? Are the flow rates being seen what you expect?

3. What temp is the heat source flowing at i.e. boiler?

[JohnMo]

50 minutes ago, NoelM said:

floor gets tepid (~25 degrees) but never warmer and this doesn't seem to be enough to keep the (glassy) room warm on winter mornings, even with the UFH turned on 24/7

Floors should never get hot. Your mixer always mixes return water with new hot water. So if you have the supply water to the mixer at 45 the mixer is unlikely to give much above 35 to the floor.

 

For a given flow temperature increasing a loop flow rate will increase the heat output to the room, reducing flow rate heats the floor less.

[NoelM]

Thanks very much for the replies, @ProDave & @JohnMo! Some answers and follow-on questions below...

 

On 17/12/2023 at 11:41, ProDave said:

What do you mean by "venting the circuits"?    Do you mean flushing water through them to ensure there are no air leaks?

Yes, that's what I mean. Sorry if terminology not right.  Thanks for confirming the process!
 

On 17/12/2023 at 11:41, ProDave said:

A simple solution is to buy a cheap infra red handheld thermometer and use that.  Only then can you tell if the flow temperature is correct and being regulated properly.

Good idea. I've now used our handheld thermometer in "surface mode" and with the heating on for 10+ hours I get:
 - flow pipes at manifold: ~65°C
 - return pipes at manifold: ~45°C
 - floor temperature: ~26-27°C

Perhaps the 65°C suggests the flow temperature is actually too high (at what point could it become a problem for floor materials) and I need to turn it down a bit?

 

On 17/12/2023 at 11:49, JohnMo said:

1. No issue with the way setup, you are able to change pump without having to bleed full UFH system.

2. Are you hearing gurgling when UFH is on? Are the flow rates being seen what you expect?

3. What temp is the heat source flowing at i.e. boiler?

Flow rates seem to be adjustable as expected, though I don't actually know the lengths of the circuits (and builder/plumber is ghosting me) so I'm not sure what they should be set to. Heat source at the boiler (combi boiler) is at least 65°C - see flow and return temps noted above.
 

On 17/12/2023 at 12:02, JohnMo said:

So if you have the supply water to the mixer at 45 the mixer is unlikely to give much above 35 to the floor.

Understood, but it sounds like you'd expect the floor to get above 27°C? (Especially given it's actually fairly mild outside and warm inside at the moment).
 

On 17/12/2023 at 12:02, JohnMo said:

For a given flow temperature increasing a loop flow rate will increase the heat output to the room, reducing flow rate heats the floor less.

Thanks. I have read repeatedly things like "Too fast a flow rate will not transfer the heat properly in the room", but I confess that from a physics pov I don't understand why that would be the case. "More flow => more heat" is much more intuitive to me! 




 

[JohnMo]

28 minutes ago, NoelM said:

give much above 35 to the floor.

Should have written 'give a flow temperature much above 35.'

 

Your main issue is the delta T (difference between flow and return) should be closer to 7, not 20 degs that you have. 65 deg flow temp is just wrong it should be well below this.

 

How are you actually heating the floor? Timings etc.

What are your rooms temps with the floor at 27 degs?

What is your floor buildup?

 

 

36 minutes ago, NoelM said:

Flow rates seem to be adjustable as expected,

You don't need to flush through to get air out then

 

41 minutes ago, NoelM said:

have read repeatedly things like "Too fast a flow rate will not transfer the heat properly in the room", but I confess that from a physics pov I don't understand why that would be the case. "More flow => more heat" is much more intuitive to me! 

Makes no sense to me either.