Operating Underfloor Heating

[nirish]

I have water underfloor heating in my lofted ceiling garage conversion with two heating loops. Manifold pictured. It has Kingspan insulation underneath, a solid scree with 18mm chipboard, ply and karndean on top. It also had 9months to dry out before use.

I have been very disappointed with the heat up times, in the region of 5-6hrs before warmth is felt and hrs longer to heat the room itself above starting temperatures. I now have it on most of the day with a 21° room stat and 18° overnight.

I want to check what performance should be expected and what if anything I could change.

The blue dial can't be set higher than 4.5/6 which has the water temp at 45°

It can't be seen in this picture but the flow rate was left wide open at max flow by the installer. I wondered if this was an issue and tried 2L/min as recommended online but this seemed to make it worse!

Any thoughts/help massively appreciated.

 

[Mr Chibs]

Me personally I’d say it’s the plywood and karndean flooring. As wood is a poor conductor of heat.

On mine after the screed is decoupling mat and limestone tiles.

The heat up time is quick, which surprised me, you can feel it warming after an hour ish.

And at the moment it comes on for an hour or so min the morning and hasn’t come on again until the next day.

floor area around 28 sq m.

For all that said once yours is warm, I presume it stays that way? At least the warmth is in.

 

[Mr Chibs]

Forgot to ask, is you insulation under the screed or under the slab?

Under screed ones will heat up quicker.

 

[Exedon]

First you are operating it correctly we are registered polypipe underfloor contractors they recommend a 4 degree difference between occupied and back set temperatures so your just about there.
Slow heat up as has been said timber thickness wont be helping.
What temperature is boiler flow into manifold unit?
Typically needs to be 15 degrees above your intended outgoing underfloor temperature.

 

[nirish]

@Mr Chibs you've succeeded in making me feel even worse about this, yours heats up in 1hr? The insulation is under the screed.

My experience today with running it constantly all day is a feeling of slight warmth in the floor after 4hrs, then subsequently heating the room from 17 to 19.5 The worst part is the thermostat is set to 21 and it seems incapable of heating the room to that degree!

@Exedon thanks for the reply, how do I see boiler flow temperature into the manifold unit?? The two thermostats on the manifold itself are now 48 and 47 but I assume this is the outflow and return from the underfloor pipes? The slow heat up is a big issue and another seems to be that it is struggling to heat the room itself to the requested 21 despite having been on for 10hrs straight!!!

 

[Mr Chibs]

Not intentional, I’m sure yours will get tweaked.

I find with mine I don’t need it at 21° like a room with a radiator, as the heat is floor to 6ft high.

I have it set at 19° currently, and come 10pm its set to be able to go down to 15° Overnight and back to 19° in the morning.

As I type this, it’s 19.5° And it’s been off since this morning about 7am.

Think there are 3 stages on my pump, I’ve got it on 2.

Is the slow heat up you have a problem?
It’s perhaps a case of setting it to come on earlier etc.

 

[Exedon]

To measure flow temperature you would typically use a clamp type thermometer (should have been checked by your installer)
Don't by any chance have pictures of underfloor before screed was put down? How far apart were underfloor loops?
Was the system properly designed by wavin or is it a single room pack that's been put in?

 

[nirish]

@Mr Chibs I guess every room is different but ours feels fresh at 19.5 which is the max temp the room has reached depsite running it for 12hrs solid. It's been 19.5 for the last few hours. The heat up is so slow that it's an issue and the max temp perhaps more so.

@Exedon I'm afraid I have no pictures or much info relating to layout and design, it was installed by a specialist who was contracted by my garage conversion builder and carried out when I was working. I am unaware of an clamp thermometer too.

 

[Exedon]

I would suggest you contact the underfloor installer they should be able to tell you the lengths of each circuit it's then very easy to calculate the heat output available to you.
If your struggling to get up to temperature now needs sorting before it gets cold!

 

[Mr Chibs]

So when you say running for 12 hours solid, the boiler is not heating the water for most of that time is it?

Could it be that the pump is running but boiler not firing?

 

[winston1]

The big snag, con even, with underfloor heating, hysteresis. Takes ages to heat up and cool down. Great for a nursing home where it is on 24/7, crap for a domestic house as it has to be on much longer than conventional radiators.
My advice would be to cut your losses and put a rad in.

 

[Mr Chibs]

Sorry Winston, but not sure that’s true.

cool down yes it’s slow, but you don’t want it quick when it’s cold.

 

[Swwils]

What flow temp was the floor designed for

What flow temp is the floor actually getting

 

[nirish]

@Mr Chibs the room thermostat is set to 21 which the room never reaches, so the underfloor pump is continously running and the flow temp is always 48degrees so I assume the boiler must be firing to achieve this.

@winston1 I'm afraid that isn't helpful in any way, after much research it was clear that underfloor heating is the most effective way to heat a high vaulted ceiling room as the radiative effect warms the lower space more than convective heat from radiators which all instantly rises to the ceiling. Clearly mine isn't working efficiently enough to meet the demand which is incredibly infuriating but I don't think ripping it out should be the first port of call.

@Swwils I'm afraid I wasn't given any of this information or any information really regarding the install. It looks like I'll have to get in touch with the builder who contracted the underfloor heating to get any answers

 

[Exedon]

Just to run through how we do underfloor installs.
After commissioning we call over a number of day to build temperature up slowly. When complete we give the customer a folder (normally email) that includes design criteria heat loss calculations all manufacturers instructions and photos of install at all stages and guaranteed certification.
As your system is clearly not working how you want it to time to get installer back.