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Simple setup with willis heater & 2 zones


Buzz11
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Thanks to the pioneers here that posted so much detail on their willis heater setup that I followed in their footsteps and so far so good!   Especially @TerryE and @Jeremy Harris


Like some previous posters & bloggers, I live in a low energy house (passive standard but not certified) which was built in late '14. For the first 6 years we've relied on a stove as our primary heat source backed up by 900w heater element in our MHV unit, however the arrival of 2 daughters has meant we require a slightly higher house temperature and the stove poses a risk to curious toddlers so best not to rely on that for routine heat.    Luckily due the foresight of the builder, pex pipes were laid into the foundation so I went ahead and had a simple under floor heating 'arrangement' installed -- pretty much copying whats been posted here before.


I've also attached photo of the pipe layout in the foundation and the drawing, I'm curious to see what people think. 


The system was installed last week and was set to 30° but this is actually working out at 23 to 25c  (I presume the immersion thermostat isn't very accurate) After about 6hrs the heat was noticeable in the house and after 24hrs it was becoming a bit too much -- room temperature was climbing to 23c so I turn off the immersion during the day and now it just comes on at night (12 to 8am) 

I've read in various places online that UFH water temperature is typically 30 to 40c and I seem to be operating much lower that that, I presume due to the makup of the foundation (floor area is 125m²)


At this early stage, I've a few questions that perhaps someone could give me their opinion on;

 

 1. Do I need a manifold?  The wavin gear looks pretty good in this video. I'd like to be able to monitor the flow & return temperatures so the gauges would be handy.

 

 

 

2. I now need a thermostat, just one will do the job since the ground floor is mainly open plan and the house has MHV so air movement is good. I'm considering the Google Nest, Which? gives it a good review.

 


3. When I've the thermostat operational, should it activate the pump and immersion together so they turn on/off at the same time or should the pump run a bit longer after the immersion turns off

 

4. So far, I've noticed the flow and return temperatures are very similar, I'd expected there to be differential of at least 5 or 10 degrees but I'm not seeing that.

 

Thanks for reading.

 

 

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Edited by Buzz11
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Welcome to THE forum for people like us! 

 

What a deliciously simple setup you have installed and it sounds like the house overall works well. The amount of pipe in slab is quite low, some may say too low but the proof may be in some of the other things you tell us, but again that seems to be working if you can get the temperature up as you describe so all you need now is to get control of it.

 

1. It does not sound like you need a manifold but, see 4 below, you probably need to check the floor temperatures across the two zones to check they are even.

2. One stat will be fine, NEST is a good system but naturally it comes with the Big TECH downsides of privacy etc. You may need to control the water temperature at the Willis so you don't end up with the water temperature running away. This will control the air temperature - however you may also want / need to control the water temperature / slab temperature.

3. Cannot see a massive need for run on, what would that do or not do once the heat is off nothing will get any warmer.

4. Several things. A. The slab is at the water temperature (I think JS Harris had his at about 23) if that is even then all is well, sort of, you have the Willis water temp stat controlling the slab. B. The water is all flowing round the shortest loop and as it is so short it does not have the contact time to give up its heat to the slab - hence check the slab temps but you may improve things by playing with the pump speed. C. This may then lead to the need for a manifold to balance the two loops. All need you to find out how close the actual slab temperature is to the water temperature you are putting in and how the two zones are balanced (Some balancing might be achieved using the ball valves you have although this would be relatively crude.

 

 

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I would have thought the basics are

1. Simple manifold so you can flow balance, actuator of each loop, all wired to act as one, from single thermostat. A simple UFH wiring centre, that would manage the thermostat, actuators and pump, possibly a relay to manage the heater, using the wiring center CH signal.

2. Single simple thermostat, I'm using a Salus wq610rf, set to 0.25 hysteresis. £60. You can move it around the house to find the best location, before committing to holes in wall.

3. A mixing valve upstream of pump, to give you protection if the thermostat in the Willis heater fails.

4. Pre installed (spare) second heater, valved to be put online should the first unit fail.

 

 

 

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Hi @Buzz11

You are doing so well, and the info @MikeSharp01 and @JohnMohas just supplied is so good, that I have little to add except about the builder adding Pex pipes during the slab construction, and that is you were really lucky!

 

I would be very interested, once you control the temp a little better, to know how the slab temperarure feels from place to place as the pipes are alot further apart than a lot of designs.

 

I wonder if the closeness of the pipes relates more to the speed of temperature rise rather than overall slab temperature. 

I wonder what floor coverings you have as well.

 

Perhaps you will update further down the line.

 

Marvin 

Edited by Marvin
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34 minutes ago, MikeSharp01 said:

NEST is a good system

 

NEST is a good system but it's an 'intelligent' one. So can 'learn' what it thinks you need in terms of control.  The way it learns is pre-programmed, so if the learning algorithm doesn't suit your heating setup then it will work against what you are trying to achieve.  I don't think they work well with ASHPs for example.  Having said that, your system is much like a system based on a gas boiler - you can turn the heating element on and off as much as you like/need, so it should be OK.    We're going to use a couple of simple thermostats on our system to control 2 zones. 

 

Simon

Edited by Bramco
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£127 for a 2-port manifold. Deffo needed for balancing / reading the flow rates. Trying to regulate the flow with ball valves will be horribly coarse, and offer little help for the effort whatsoever. I use Komfort manifolds Link as the air vent is at the same height as the head of the rail, so these vent far better than others where the ends reduce and step down ( trapping air in the top of the rail ).

It is un wise to connect the Willis to the slab with total reliance on the in-built stat, so I would recommend either adding a TMV and pump to compliment the manifold, or, at the very least, I would fit a pipe stat to the return pipe and set it to break at 30oC. That would at least protect the floor covering and occupants if the Willis stat snuffs it in the closed position. 

 

Very little pipe volume in the floor, but it is what it is. Deffo needs balancing with the manifold though.

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Agree on the manifold and use of a pipe stat here, but do not go with self balancing actuators or anything clever with a Willis as they will potentially trip the stat if the flow reduces and you get stagnation. 

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Thanks folks for all the replies so far ?

 

Manifold or not: I'm convinced now that I should go for manifold mainly because the two zones are crudely divided as 'front' and 'back' of the house, the front being East facing so a bit cooler, the back is west facing and has more windows so greater solar gain. Its likely that I'll need more control at some stage so best to have it installed now while I have the plumbers attention and open invoice book!

 

Slab temperature;  unfortunately the entire ground floor is covered with engineered timber floor except the utility room which is tiled so I'll get a true reading there. I'm going to open the kickers in the kitchen to see if I can access the concrete floor and take readings there.  I have noticed hot spots when barefoot and I could probably trace a pipe by following the heat. According to the 'as built' drawing the 2 zones are equal at 65m each, the pipe is 1/2" so that works out at .12L x 65m = 7.8L of water per zone, say 16L of water in total for the willis to heat so it'll have an easy life!

 

Water thermostat;  yes totally agree with advice that the immersion thermostat shouldn't be relied upon and the manifold with blender/mixer/diverter (not sure what its called) should provide much more accurate temperature control than the immersion.

 

Room thermostat;  @Bramcothanks for the tip on the Nest intelligent feature -- I don't want to be fighting the thermostat and paying a high price for the privilege!  @JohnMo thats a lovely looking unit and I'll certainly look into that further.

 

 

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If you add the TMV and pump set with the manifold, remember it needs to be a low temp setup. The Ivar Link has the thermo probe + TRV instead of a thermo-mechanical mixing valve. Select the option for 20-60oC temp range on the TRV and that will give you very accurate flow temp control all the way down to its lowed street setting.

Also, I set these up to have the primary pump recirculating water directly back to the Willis heaters to keep a constant flow of water and to reduce kettling. From the recirculating loop, you then tee off twice, once for UFH manifold / pump set flow ( immediately after the Willis heater(s)) , and the UFH return gets teed back into that loop immediately before the return goes back into the primary pump. I wouldn’t set the Willis up with the flow arrested by a TMV.

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On 28/02/2022 at 16:43, Nickfromwales said:

If you add the TMV and pump set with the manifold, remember it needs to be a low temp setup. The Ivar Link has the thermo probe + TRV instead of a thermo-mechanical mixing valve. Select the option for 20-60oC temp range on the TRV and that will give you very accurate flow temp control all the way down to its lowed street setting.

Also, I set these up to have the primary pump recirculating water directly back to the Willis heaters to keep a constant flow of water and to reduce kettling. From the recirculating loop, you then tee off twice, once for UFH manifold / pump set flow ( immediately after the Willis heater(s)) , and the UFH return gets teed back into that loop immediately before the return goes back into the primary pump. I wouldn’t set the Willis up with the flow arrested by a TMV.

 

Excellent thanks for that and the link.   Can I check my understanding in laymans terms;

1. The thermo probe & TRV will give more accurate temperature control.

2. Water needs to be circulating through the willis regardless of whether the TRV is open or closed in order to prevent the willis turning into a hand grenade!

 

Once this is installed, what temperature would you set the willis thermostat to?  I'm guessing maybe little bit above the desired floor temp?  I assume there's no benefit to having it too high because the TRV/manifold is controlling the temperature and the willis is just supplying hot water a bit above that.

 

I'd like to give the plumber a diagram showing the 2 x tee off's -- in fairness to him, he was very curious whether our basic/temporary setup would work or not and he phoned me after a few days to ask 'could I feel any heat yet?'   my reply was eh yeah, it was too hot! I had to turn it off!  😉     He said he'd never seen or fitted such a simple UFH setup, the usual installation has lots of zones and masses of heat from heat pumps etc

 

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37 minutes ago, Buzz11 said:

1. The thermo probe & TRV will give more accurate temperature control.

Yes, and near silent in operation. Regular TMV's often start to choke the flow and make a lot of noise when asked to sit at their lowest setting.

38 minutes ago, Buzz11 said:

2. Water needs to be circulating through the willis regardless of whether the TRV is open or closed in order to prevent the willis turning into a hand grenade!

Steady on Buzz......nothing is going "to infinity and beyond" ;) The Willis will be a little less 'erratic' with a constantly recirculating body of water going through them at a regular pace.

 

Some more of my waffling can be found here;

 

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58 minutes ago, Buzz11 said:

Once this is installed, what temperature would you set the willis thermostat to?  I'm guessing maybe little bit above the desired floor temp?  I assume there's no benefit to having it too high because the TRV/manifold is controlling the temperature and the willis is just supplying hot water a bit above that.

As close to the desired flow temp as possible. That will stop the thermostat clicking in / out as much.

59 minutes ago, Buzz11 said:

I'd like to give the plumber a diagram showing the 2 x tee off's -- in fairness to him, he was very curious whether our basic/temporary setup would work or not and he phoned me after a few days to ask 'could I feel any heat yet?'   my reply was eh yeah, it was too hot! I had to turn it off!  😉     He said he'd never seen or fitted such a simple UFH setup, the usual installation has lots of zones and masses of heat from heat pumps etc

Sounds like a decent guy tbh.

image.thumb.jpg.8c3330e1374a2d6938125bf2c56994dd.jpg

 

It's as simple as that.

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31 minutes ago, Nickfromwales said:

As close to the desired flow temp as possible. That will stop the thermostat clicking in / out as much.

Sounds like a decent guy tbh.

image.thumb.jpg.8c3330e1374a2d6938125bf2c56994dd.jpg

 

It's as simple as that.

 

 

Many thanks for that -- brilliant.

 

I'm really grateful for the help on this thread and all the others inc blogs etc which provide really useful information - thank you 👍

 

I remember when we were fitting out this house in 2014, I needed a stove with a low output (the house needed 2kW heat for the coldest 3m of the year) so I started phoning around "Have you got any low kW output stoves, say 2-4kw?" and the answer nearly ever time was "nah thats not right, surely you mean 12 to 14kW...theres no way 2-4kW could heat a house"  yet here I am with a 3kW willis and its turned right down so we don't overheat ! 

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  • 1 month later...

Few more questions for the Oracles 😉

 

Cooling: Summer overheating is a major problem in our house caused by large south facing windows and high levels of insulation so could underfloor cooling work?  I could circulate cool mains water through the slab and dump it out a waste pipe nearby,   would this work?   It would be a waste of water but we'd only need it during hot spells which only last a week or two at most.  I've read about the dangers of creating a due point which could damage timber floors so I'd need to watch out for that but in some limited googling I haven't found any information on under floor cooling with mains water.

 

Shelly controls:   I've bought a Shelly Humidity & temperature sensor which is a brilliant piece of kit plus really good value so I'm going to use that along with a relay to control the on/off temperature & timer requirements.

 

Shelly also sell a TRV which would be an interesting way of controlling the underfloor water temperature but while it has digital controls, I don't know if it digitally controls the water temperature?  it doesn't appear to have a thermo probe so how is it accurately measuring the water temperature?

 

https://shelly.cloud/shelly-thermostatic-radiator-valve/

 

https://shelly.cloud/products/shelly-humidity-temperature-smart-home-automation-sensor/

 

 

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