Underfloor heating system not very efficient - what can i do

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Hi All.

WE have got underfloor heating on the entire groundfloor of the house, it was done to building regulations spec that is the insulation which if i remember is 100mm celotex, and a screed of 70mm + tiling.

The problem now is that it cost a fortune in gas to heat the space, there are 4 different thermostats covering the space and one upstairs for the radiators.

It takes just over an hour for the heating to be relevant, lets say 80 mins after coming on, I set the boiler to Eco mode as it was on maximum before, I also set the mixing valve to Max, so adds little or no cold water from what I read.

Today for example, It hasn't been cold, very mild 10- 12 deg outside, I set it to come on for 2hrs, it uses 53Kw of gas costing around £2.40. I know the cost of energy has gone through the roof, but this is when I need my heating to be efficient.

Setup

S plan system with underfloor heating downstairs, radiators upstairs and one backup radiator downstairs.
Unvented hot water cylinder 300L
Underfloor heating system with 4 zones/4 stats and one stat dedicated for radiators.


Observations.

  • When the heating is on, almost all the pipes are hot. It makes me think, i hope its not heating the cylinder also.
  • I do not trust the installation, over 8 months ago, when gas bills was averaging about £400 a month, upon investigating it turns out that the flow & return pipes were mixed up :cry::eek:, the plumber I called then wasnt an UFH specialist but I was grateful for his discovery and fix to swap it around. He also fitted a temp gauge on the flow valves, so that one can monitor the temperature.
  • From the gas usage, is this as expected ?. I don't know.
  • I want to engage an underfloor heating specialist to service & look at the system again but before doing so, I would like to get the views from the pros on the forum.
  • I have now set the UFH to come on once a day, temp set to 19.5 deg whilst the kids are on holidays and are at home more often, when they are in school I set it to come on at 2pm just before the get back from school and that runs till about 6pm @ 19.5 deg.
  • The unvented hot water system is scheduled to come on at around 6am daily.
  • I tried to balance the system by opening the valves for zone A and Zone B up so they get hot quicker, I don't think I did a good job here. I managed to drain the system out and quickly put it back as i panicked.
  • My zone valves have dirty water inside it and i am not sure they work as they should do or work like the ones I have watched on youtube.

Zone layout

upload_2021-12-27_23-34-56.png



Zone valves, turn it down or up. the level remains thesame.
valve.JPG
 
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What ever type of heating is used, it is the losses that matter. Three ways to loose heat, convection, conduction and radiation. Well also a forth simply pumping the heat outside. Unless using inferred heaters loss by radiation is unlikely, so first consideration is air changes, we need air changes, but we want to reduce heat loss, so heat recovery units are the way to go so still have air changes but reduce heat loss.

Convection is not so much as a problem today, when we had single glazed windows we wanted to reduce air movement near to windows, I had in the late 70's a house with warm air central heating, cost a fortune to heat as the fans circulated the air past the cold single glazed windows, where when using radiators you get a convected flow. circulation.jpg

So position the radiator 90° from window and the area by the window can remain cold, but the rest of room can be quite warm, we are told to fit thermostat on opposite wall to radiator so in the air flow, but does not get direct heat. I know with mothers living room thermometers placed around the room could measure 18°C to 28°C in the same room at the same time, due to how the thermals circulated the air, and also the way the sun shone through the bay window.

For that room speed was the essence, we needed a fast acting heating system, I used an electronic TRV head to speed up reaction time when the sun came out. For that room UFH was a non starter, however the other rooms did not heat up so fast.

Kitchen in the main has some other form of heating, so again we use some thing fast acting, fan assisted kick space heaters for example.

So the aim is not to over heat any room, but there are more ways than one to skin a cat, and careful timing can reduce losses, so if cooking at 5 pm set heating to stop at 4 pm in kitchen. Some town houses are in shadow all day, they get light but no direct sun light, my last house the semi-detached neighbour was to South, so house got very little heat from sun.

House before that, when the semi-detached neighbour left the house and it went on the market for 3 months before being sold, our heating bill soared. We had never realised how much heat transferred thought the party wall, which unlike outside walls did not have a cavity or of course cavity wall insulation.

It also pointed out how 1°C can make a huge difference, neighbour set their heating to 22°C and we set ours to 18°C so they were helping to heat our house, when they were evicted heat transfer reversed we were heating their old house. If you can hear your neighbour likely also heat transfer, fitting sound deadening and heat retaining wall covering can make a huge difference.

Main point is a heating system is designed, not thrown together, the guys who design it are called heating and ventilation engineers, and engineer to my mind means University trained, level 5 or above, yes I am level 5 but in electrical not heating and ventilating. Note how heating and ventilating goes hand in hand.

Yes poor installation can reduce efficiency, but two things, easy to test, one no room too hot, and two return water to boiler needs to be cool, if return water cool then boiler will be extracting the latent heat from flue gases, and if no room over temperature then control is correct.

This house the heating turned down 11 pm and my bedroom still warm at 4 am with no heating running for 5 hours, OK warm outside 8°C, but house is both slow to heat and cool, with 100mm celotex heat should not be going down, so where is it going?

My DHW in summer is heated 4 times a week 20 minutes at a time, tank not well insulated, but heat does last 2 days, so turning it on/off in winter seems pointless, heat from tank which is in a central room will heat the bedroom, bathroom, and landing which surrounds it. So heat not lost.

I set over night at 17°C in hall and during the day it raises to 19°C, other rooms may be warmer or cooler, all have programmable TRV heads, but the hall rarely cools to 17°C the heating has most days started the 0.5°C at a time climb to 19°C before heating cuts in.

I don't personally like UFH to my mind it is too slow to react, however your not complaining about over shooting so if not over heating rooms, your looking at where the heat is escaping rather than what is wrong with heating.
 
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Your last picture hasn't posted. I think the first thing to say is stop fiddling with it. The blending valve should not be at maximum, it should be set correctly for the system, hopefully where the commissioning engineer left it. Same goes for the flowsetters on the manifold - they should have been set correctly according to the system design and should not be altered.

UFH isn't designed to be turned on and off, it's inefficient to run it that way. Have a daytime comfort temperature and a night time setback temperature a few degrees lower. Once it's gently warmed the slab and found its equilibrium, running costs will reduce.
 
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Your ufh is a lot more complex than mine, I have it in one part of the house and radiators in the rest.

Gas usage is not an issue in my installation. I was under the assumption it should be economical to run.

I think you need to think
Of the ufh differently though, it won’t heat like a radiator, and should not be controlled like one.
If I set mine to say, 19° I allow the thermostat to decide when it needs to come one/off. In milder weather this maybe once a day, on colder Days possibly it comes on again in the evening.
The goal is to keep the room to 19°

I have a fallback temperature to 15° Overnight, so not to start the next day with a really cold floor.

I have blending valve on a medium, but my combi is heating to around 50° Before the blender needs to lower slightly.
 
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Your last picture hasn't posted. I think the first thing to say is stop fiddling with it. The blending valve should not be at maximum, it should be set correctly for the system, hopefully where the commissioning engineer left it. Same goes for the flowsetters on the manifold - they should have been set correctly according to the system design and should not be altered.

UFH isn't designed to be turned on and off, it's inefficient to run it that way. Have a daytime comfort temperature and a night time setback temperature a few degrees lower. Once it's gently warmed the slab and found its equilibrium, running costs will reduce.

Thanks for the response, I have now fixed the issue with the last picture now displaying properly. When you say that the UFH isnt supposed to be turned on/off. I get what you are saying, but what am i supposed to do in a case like this, spending £300 a month heating a house is not practical. Our routine is as follows, when the kids are in school and I am working from home which is everyday in the current climate, there is nobody at home fro 8.30 till 3pm. The kids get back around 3.30pm and are up till about 8.30pm after which time they go to bed, I work from my outbuilding which has its own heat pump, this is the reason why I think heating 100sqm when nobody is in the house from 8.30pm - 3pm doesn't really cut it for me. We are mainly downstairs from 3.30 till about 11pm. The radiators upstairs come on from 8 - 9pm just as the kids go to bed.

What do you suggest as a schedule ?
 
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Your ufh is a lot more complex than mine, I have it in one part of the house and radiators in the rest.

Gas usage is not an issue in my installation. I was under the assumption it should be economical to run.

I think you need to think
Of the ufh differently though, it won’t heat like a radiator, and should not be controlled like one.
If I set mine to say, 19° I allow the thermostat to decide when it needs to come one/off. In milder weather this maybe once a day, on colder Days possibly it comes on again in the evening.
The goal is to keep the room to 19°

I have a fallback temperature to 15° Overnight, so not to start the next day with a really cold floor.

I have blending valve on a medium, but my combi is heating to around 50° Before the blender needs to lower slightly.

Does that mean that you set it to 19 deg, all day ? So the stats will tell the boiler when to come on/off ?
Do you have any off period, I set mine to 19 deg when I know I will be in the room but 15deg during off periods. Its just that currently its not set to 19 deg all day.
 
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Concerning heat loss, I like to think I have done practically all I can. Please see below for summary.

  • In zone A, by the by windows the external facing wall is insulated internally 60mm celotex + 25mm insulated plasterboard to overboard it.
  • In zone B, external facing walls insulated similar spec to the above.
  • Suspended flooring insulated for sound mainly.
  • All the zones A,B,C,D,E all have concrete floor with 100mm celotex insulation.
  • Zone D and E have new cavity wall construction
  • Zone E has a flat roof construction.warm roof with 120mm celotex.
  • The only section of solid wall we have left is in zone D, by the flank wall by the garage, there is a big O in the garage, this is where the boiler is and the manifold/mixing valve. That section has the original solid wall construction.
  • Perhaps one mistake in hindsight is the location of the mixing valve, originally the designers wanted to site it under the stairs which I assume is a little central. However that's where the electric meter is, and the electric feed coming into the house. I was not comfortable with siting a wet underfloor heating manifold there. Another place in hindsight now would have been at the bottom of zone B near where the thermostat is, that is currently our utility room.
  • Looking at the design, the boiler/manifold is in the garage where i have placed a round O, heating zone A would be a struggle due to the distance.
  • Please see the picture of the mixing flow valves.

On a separate note, I have called 2 heating engineers this morning and hope they return my call to come and look at the system holistically. However from what I gather here, the mixing valve should not be set to max, so I have reduced it to 48 deg as a google search suggested, that's what it should be.
 
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What insulation was installed under the floor before the UFH pipes were laid?
What floor coverings do you have?

Nozzle
 
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100sqm on the ground floor only?
You sure about that?

Looks only half of that on your drg.

Do you have a performance spec and manual for your new system (i doubt it but you can ask the installer for the calcs he used).

You can then see what you have vs what you are expecting.

You can check the heat loss calcs done, see if that matches the system installed and then you have a base point to look further at the issue.

Do your own, detailed heat loss calcs (easy enough). This will also have the added benefit of educating you about heat loss.

After that, you will have an idea of how well your system is designed.

What is catching my eye is your comment about money. To make that comment, you must be aware of a significant increase in actual gas usage. (Not just guessing).

If that is real data , then simply you are heating your house more than you used to. Perhaps you just didn't heat the whole house before? Perhaps you are now heating the house longer than you did before?
Its hard to not see that you are somply heating more/longer and you don't realise it. You have improved the insulation in the area. Your heat loss is less, not more.

As i have learned recently, heating improvements don't necessarily mean using less, it can mean than the heating is more consistent and reliable.

So, you've two issues.

1) Cost expectations.
Rethink your logic on this one. Should you actually be using less gas?

2) Control and operations difficulty.
Refer to point 1. Get that fixed in your head 1st. Get the system set up correctly, meaning how you WANT it to work, then leave it for a period. Do a analysis of the heating and cost profile. If it's right, then job done.


You have a problem with trusting the installation. Find a person you can trust to help set it up and maintain it and you remove one of the variables.
If it were me, i would be studying the system myself, getting the calcs from the installer, checking them, reviewing the OEM files, etc and looking to check it myself.

Best of luck.
 
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100sqm on the ground floor only?
You sure about that?

Looks only half of that on your drg.

Do you have a performance spec and manual for your new system (i doubt it but you can ask the installer for the calcs he used).

You can then see what you have vs what you are expecting.

You can check the heat loss calcs done, see if that matches the system installed and then you have a base point to look further at the issue.

Do your own, detailed heat loss calcs (easy enough). This will also have the added benefit of educating you about heat loss.

After that, you will have an idea of how well your system is designed.

What is catching my eye is your comment about money. To make that comment, you must be aware of a significant increase in actual gas usage. (Not just guessing).

If that is real data , then simply you are heating your house more than you used to. Perhaps you just didn't heat the whole house before? Perhaps you are now heating the house longer than you did before?
Its hard to not see that you are somply heating more/longer and you don't realise it. You have improved the insulation in the area. Your heat loss is less, not more.

As i have learned recently, heating improvements don't necessarily mean using less, it can mean than the heating is more consistent and reliable.

So, you've two issues.

1) Cost expectations.
Rethink your logic on this one. Should you actually be using less gas?

2) Control and operations difficulty.
Refer to point 1. Get that fixed in your head 1st. Get the system set up correctly, meaning how you WANT it to work, then leave it for a period. Do a analysis of the heating and cost profile. If it's right, then job done.


You have a problem with trusting the installation. Find a person you can trust to help set it up and maintain it and you remove one of the variables.
If it were me, i would be studying the system myself, getting the calcs from the installer, checking them, reviewing the OEM files, etc and looking to check it myself.

Best of luck.
For now all I can do is study the system myself. I cannot get hold of the contractor who did the installation to get the calcs etc.

I will feel better if I can get a pro to evaluate the system and set it up correctly.
 
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I'm not kidding...a lot of installers are so stressed out this time of year they'll block your no.
The public text/email/phone for quotes all over the holiday period and many of us use that as a guide to the customer....ie. forget it.

With the insulation you have your bills should be minimal but unless done properly it could be worthless.
Are you checking the gas usage by calculation from your own meter readings (directly off the meter) or relying on a hopeless energy companies smart readings?
I'd also look at the hot water expense...plenty of kids will stand under a shower and use ALL the hot water in the cylinder...I've had complaints from customers
having inadequate hot water provision until we discover what's actually going on. 8 litre/min flow limiters is perfectly adequate.
 
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I'm not kidding...a lot of installers are so stressed out this time of year they'll block your no.
The public text/email/phone for quotes all over the holiday period and many of us use that as a guide to the customer....ie. forget it.

With the insulation you have your bills should be minimal but unless done properly it could be worthless.
Are you checking the gas usage by calculation from your own meter readings (directly off the meter) or relying on a hopeless energy companies smart readings?
I'd also look at the hot water expense...plenty of kids will stand under a shower and use ALL the hot water in the cylinder...I've had complaints from customers
having inadequate hot water provision until we discover what's actually going on. 8 litre/min flow limiters is perfectly adequate.

I am checking the gas usage by looking at the smart meter display unit. Should i be reading off the actual meter ? I found the smart meter stuff easier, with the meter, one will need to convert the readings to Kw/hr to work it out etc. The smart meter does all that for me.

The hot water cylinder, normally it runs for an hour every day, we don't run baths, all showers a household of 5. On average, once the cylinder runs for an hour, the usage comes to about 26kw for just the cylinder. If there is not a lot of plate/hand washing, the cylinder can last for more than a day. Today for example, Its switched off and the hot water still lasted for the kids to shower, the reason i have not really experimented with not running it everyday to check how long 300l can last for is because I dont want the kids waking up and no hot water or wife waking up to shower and no hot water on way to work.

In terms of a schedule/temp setting, what do you suggest please ?
 
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