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Hi all, first post on here - really hope you can help.

We have recently moved to a newly converted barn (single story) which has a Polypipe under floor heating system heated by an ideal system +24 boiler. It is quite a large property (the barn is 22x5x6.5) as well as a similarly sized extension. There are 3 manifolds in total - 1 x 5 port one that feeds the main barn, 1 x 9 port one that feeds the extension and 1x 2 port one that feeds the mezzanine floor area.

We have been experiencing astronomical gas consumption (£300+ per month 110000kwh usage per year projection!) and upon investigating we have established that when the system is calling for heat at the two furthest points (I.e through both the 5 port and 9 port manifolds) it is dropping the temp of the boiler like a stone (low 50 degrees ish) so consequently the boiler is working overtime to compensate for this and the rooms are the struggling to reach temperature (hence the high gas consumption!?). When the boiler drops temp the barn can take a good 4-6 hours to increase room temperature by 1.5 degrees yet when the 9 port manifold is isolated/not calling for heat the barn temperature will do this in around 1.5 hours.

The plumber who installed the system has been advised by the Polypipe dealer to fit a low loss header to the system to rectify the issue. The thing is, I have had a contradictory diagnosis from another plumber who has suggested that a low loss header is not necessary/will not fix the problem and in fact the route cause of the issue is due to the diameter of the feed pipes from the boiler to the manifolds (which is particularly relevant I guess given the 9 port manifold is approximately 12meters from the boiler) The pipe work is 22mm copper out of the boiler but then disappears into the loft in plastic speedfit connections (which apparently are also further reducing the flow).

This is our dream house that we have waited 2 years to be finished and poured all our money into, as well as our first experience of ufh; I really hope someone can help as we can’t continue to pay those sorts of bills and we don’t know who to believe / what to do for the best :( :(
 
Floor preparation and insulation is the most important thing here is it a project you had commissioned? I have experience of these type of systems and UFH is the only real way of heating such a space but the property needs to be able to hold that heat the usual way is to insulate the walls , ceiling and floors with Celotex type insulation was this done ? if not then the rooms will never reach there optimal temperature and the boiler will never turn off, can you post some pictures please . Regards kop
 
Hi Kop

Thanks for your reply. The system was designed by Polypipe and the insulation is to latest building regs (the ufh pipes are laid on 100mm insulation boards with 70mm screed if I recall correctly). I really don’t believe the issue is insulation as the barn holds the temperature for most of the day once it’s warm so - the issue is it struggles to reach temperature when there is this extra demand on the system from the extension and the boiler temperature plummets. If the boiler temperature doesn’t drop then the barn temperature can be lifted easily in around 11/2 hours?
 
How are you using your system? Are you setting your desired room temps and leaving it on constant or are you timing your heating to come on twice a day?
 
How are you using your system? Are you setting your desired room temps and leaving it on constant or are you timing your heating to come on twice a day?
That was my question too. If the op turns it off it will take ages until he really reaches the desired room temperature.
 
As KOP has mentioned above, it does make a huge difference on insulation. Furthermore it’s important to know what type of windows do you have single, double or triple glazing? Is there any insulation at the walls or ceilings? If so how thick is the insulation and what type did you use. The plumber who has suggested a low loss header is quite right. I personally would have used a low loss header too but in the same time I would have used a different boiler to reduce the gas consumption annually. With the right controller and boiler you could let the boiler run continuously. For example I installed a boiler which had over 9200 working hours but run on very low kilo watts. The boiler I installed was able to modulate itself and therefore reduced the amount of gas usage. But again, there are many factors which are very important to achieve that. You should not let the boiler switch off if you have only ufh. Once it’s cooled down it will take ages to get back to temperature.
 
Where in the Country is this, is it remote, exposed or part of a group of Barns?
What temperature are you trying to get to and what is the actual measured temperature?
Does it eventually get all areas up to temperature?
 
The plumber who has suggested a low loss header is quite right. I personally would have used a low loss header too but in the same time I would have used a different boiler to reduce the gas consumption annually. With the right controller and boiler you could let the boiler run continuously. For example I installed a boiler which had over 9200 working hours but run on very low kilo watts. The boiler I installed was able to modulate itself and therefore reduced the amount of gas usage. But again, there are many factors which are very important to achieve that. You should not let the boiler switch off if you have only ufh. Once it’s cooled down it will take ages to get back to temperature.
Beat me to it, UFH is likely to give a temp diff of 7deg C whereas the boiler is looking for 20deg C.
 
Oh and if it’s Polypipe, have the built in filters on the manifold been checked for blockages?

Ta
 
You must have a LLH installed, it will never work correctly without one.
Do you heat your hot water via a cylinder ?

That's not the issue it's the temp drop that there asking about when they open up the furthest manifold/ zone set and how long it takes to heat up

Now not saying that wouldn't help when the zones started to shut off but depending on flow rate it might not be required

Op What's the heatloss of the barn and size of the boiler
 
Sorry, you said heat loss not size, ignore everything about my previous comment except the boiler size :confused:
 
I would have fitted a heating buffer vessel the boiler would charge this to say 70°c, the underfloor heating primary supplies to the heating manifolds are then pumped from the buffer to the UFH manifolds and pump sets to be blended down and circulated through the underfloor loops, this way it reduces your energy usage and run time of the boiler . Kop
 
Remove the brass hexagonal nut at the top,that the black plug is screwed into. The filter is in there

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Barns 20x5x6.5, said it's single story so I'm taking that at 20m long, 5m wide and 6.5m high ceilings. And boilers a 24kw ideal system boiler.
You see how high your ceiling is ? By the time to reach the room temperature of e.g. 21c you definitely need a good insulated ceiling as well walls because heat will always rise. It will take ages until you reach the desired temperature by 6.5m. What’s the heat loss like?
 
Thanks all for your replies, it’s really appreciated.
I’m not sure I will be technical enough to answer questions on heat loss etc (unless someone can point me in the direction of how to work this out??)
Regarding the insulation, it has had to pass all the tests than any new build has to. The barn has been rebuilt from virtually derelict and has 500mm thick limestone walls which have all been boarded and insulated to the latest standards as well as having a complete new roof, again all insulated to latest specs. I appreciate how important insulation is but I genuinely don’t think that’s the issue as it holds hear unbelievably well.
Regarding the barn location, it is a semi-detached barn and we’re based in sheffield.

My point/question is regarding the temperature drop of the boiler and if the LLH header is required or not to rectify (as original plumber had said who has had little experience of ufh), or if it is a more fundamental issue such as the diameter of the feed pipes to the manifolds being too small which is restricting the flow?

Just to give a little more information further to my OP too, I have been experimenting with different scenarios/loads on the heating system. When all zones are open that are fed from the 9 port manifold (only, and not the barn) the boiler temperature drops down to a ridiculous 23 degrees! (This has never been tested before as we have 3 unused zones/rooms fed from this manifold). Furthermore, having isolated this 9 port manifold so the boiler just needs to heat the barn, the boiler temperature doesn’t drop at all and easily lifted the barn temp.
 
Can you further break it down to check each loop on the 9 port?
Do you have an additional red expansion vessel on the system or is it just the one in the boiler ?
Have you checked the pressure relief pipe from the boiler isn't discharging?
What is the boiler temperature set to ?
It doesn't sound right but without being on site to check a few things it is difficult from your posted info.

The one thing we can assure you of is that there needs some separation of the boiler & its pump from the feeds to each manifold.
As a few have suggested if we were designing it afresh they would be better boiler options involving boilers which can provide the heating water to the U/F without the need to mix it at the manifold. However at least for the moment I would think you want to stick with the installed boiler. This has a built-in pump which may or may not be suitable to deliver the required heating to the manifolds at peak demands, as by the sounds of it you are turning the U/F on & off.
The boiler is designed to run & work efficiently with a 20 deg drop across the flow & return, it will switch its self on & off to try to achieve this, however your U/F can't provide this as I understand it the difference is normally around 7 deg.
 
A couple of bits of info -
The design room temp for U/F systems is normally 20deg C this takes accounts of the fact the heat is mainly radiant from the floor surface not convected as with rad's etc. As upright animals with a warm brain (well some of us :p) we are more comfortable with slightly warmer feet than heads.
U/F is particular suited to rooms with tall ceilings as the air temperature at higher levels will be a lot cooler than that at lower levels un-like convected systems.
It will take approx 1 hour to raise the air temperature by 2deg C .
 
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Hi Chris

Thanks for your reply. I can check this but essentially the more load taken from each of the 9 port manifolds the lower the temperature drop of the boiler.

I can’t see anything discharging from anywhere (and the boiler isn’t losing pressure so I guess that would drop if it was?).

Boiler temp set to 75 degrees.

I have attached a pic of the tanks/vessels already fitted but no red ones?

I understand from the plumber that Polypipe / the Polypipe dealer are aware of the boiler size/spec and have confirmed that it should be sufficient but that suggestion does put something else into the mix as a possible cause .

Also, the ufh is only turned on and off by the thermostats (and have them set to 18.5 off 20 on, the ‘on/20 degree time being between 3.pm and 8.pm. With the 9 port manifold in operation and the master bedroom suite calling for heat (and subsequently dropping boiler temp) it usually takes those entire 5 hours to lift the barn temperature 1.5 degrees to 20!
 
Grey vessel is the additional heating so good (most are red, sorry)
The set up sounds right at least with the controls etc.
It would seem that a site visit from an U/F expert may be required to get to the bottom of it.
Photos of each manifold might help.
 
View attachment 36197 View attachment 36198 Hi Chris

Thanks for your reply. I can check this but essentially the more load taken from each of the 9 port manifolds the lower the temperature drop of the boiler.

I can’t see anything discharging from anywhere (and the boiler isn’t losing pressure so I guess that would drop if it was?).

Boiler temp set to 75 degrees.

I have attached a pic of the tanks/vessels already fitted but no red ones?

I understand from the plumber that Polypipe / the Polypipe dealer are aware of the boiler size/spec and have confirmed that it should be sufficient but that suggestion does put something else into the mix as a possible cause .

Also, the ufh is only turned on and off by the thermostats (and have them set to 18.5 off 20 on, the ‘on/20 degree time being between 3.pm and 8.pm. With the 9 port manifold in operation and the master bedroom suite calling for heat (and subsequently dropping boiler temp) it usually takes those entire 5 hours to lift the barn temperature 1.5 degrees to 20!
Do you know how many Liters per minute each loop gets? You should see flow regulators at the Manifold are these set properly?
 
The size of the room is relevant in relation to temperature lift of course but it lifts the temp fine in the barn when there is no demand from the bedrooms run through the 9 port manifold as the boiler doesn’t drop temperature.

I have already asked for a second opinion from aanother ufh engineer (in addition to the original installer) which is when I had received my conflicting diagnosis (one said the LLH is required, other said route cause of issue is diameter of feed piles from boiler to manifold(s) due to the long runs of pipe - hence my post on here.

Either solution ref above is a fairly major job by the looks of things and I am concerned that one or the other proposed solution (or worse still both!) will not resolve the issue of the boiler temperature plummeting like a stone due to demand
 
For us (or them) to help we would need to know the loadings (heatloss) for the zones & the pipe sizes feeding each, it is easy to work out if the supply pipework can carry the required flow of water.
Are the manifolds Flow & Returns 22 or 15mm ?
 
Gas consumption has more to do with the fabric of the building and heat loss. Not the system. But a badly set up and installed one will use a bit more.
You have a large building that will require a given amount of energy to heat it. If the building is well built, air tight and well insulated. It will be efficient. But if it’s draughty and poorly insulated, it will cost a lot more to heat to a given temp.
 
You need to get a engineer who understand how UFH works told you how I would do it my fellow members may have other ideas . Kop
 
Are there any ufh specialists on here that have had experience of larger properties/installs that are local and would be willing to commit to a diagnosis and guarantee that it would resolve the issue?
 
you can post a request at the top of the home page for a engineer bit to far for me good luck . Kop
 
do you have the plan that poly did?
 
Pictures of the manifolds as requested. The pipe work coming from the boiler to feed these is 22mm copper BUT to the 9 port manifold where it goes into the ceiling there is a section of plastic speedfit on the flow/return which I understand has quite a significant reduction in bore (which, if the fault is caused by the feed to the manifolds being compromised then this will only serve to exaggerate this issue?)

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