UFH Operation

[Ricco]

Hi

 

We completed and moved into our house in the spring, so are only having to use the heating now.

This is the first time we have ever had UFH so we are still getting used to it.

 

We have UFH throughout with a liquid screed, we have a good amount of insulation and a good level of air tightness.

 

My question is in relation to its operation - should i keep a constant room temperature 24/7 e.g. 21 degrees or use the set points in the room thermostats to set it back to say 16 degrees when out at work or not using the room. I have read that UFH should be run all the time but i was unsure if this meant to maintain a constant temperature or vary the temperature.

 

Any advice would be appreciated.

 

Thanks

[newhome]

Personally I set mine back when I’m not around as I don’t want my boiler to keep firing up. I then set it to come on again a couple of hours before I arrive home so that it’s up to temperature when I get in. The slab is slow to heat up but slow to cool down too so I don’t find that it drops too much during the day anyway. That works for me. YMMV. 

 

[BotusBuild]

Ricco,

I am assuming that the flow temperatures in the UFH are somewhere in the 35-45C range, and that the heat source is able to provide input to the system 24/7.

If you have individual room thermostats then set each one according to the temp you want, but keep in mind that if set to different temps at different times of the day, that UFH can take longer to increase the apparent temp of the room than a traditional radiator system, if the difference is more than two/three degrees.

For example, if you were to go away on a 2 week holiday leaving the temp at say 12-16C, then you would want to increase the temp to your preference 18/21/24C a day before you return to give it time to recover.

My personal preference is to only have your normal day-to-day setup with small temperature differences at different times of the day. 

 

HTH

Edited October 4, 2019 by BotusBuild

[Declan52]

I set my heating to come in at 6am when it is the time for it to come on most days, October to April depending on how cold it gets. So my boiler is fired up and heating my 350l tank. 

At 6:30 my programs for all my stats kick in. I have the living room, kitchen, sun room set to 21, the other rooms 20. If at 6:30 any stat is lower than the set temp then it will call for heat and start to warm up my slab. They will continue to call for heat until they get to whatever temp they need to be, usually takes around 60 mins before you would feel heat under your feet then maybe another 60 mins and it will have got to 20-21 and turned the demand for heat of.

The rest of the day the temp on the stats are set back so they don't call for heat unless it's really really cold as in -10 type weather. Then the next morning the cycle starts again. Some mornings depending on how cold it got during the night there might only be 1 zone or could be 5. 

So you are basically heating the slab up once in the morning, suits my family this time as the house feels warmer for kids going to school and me and the wife going to work, and then it will continue to heat the house after the stat has turned itself of for the rest of the day. 

This assumes that you have built your house to a high enough standard that it won't leak  like a tea bag. 

[ProDave]

I think it depends on just how well insulated your house is.

 

I have my UFH on only in the daytime.  There are 2 reasons, one is if there is any useful solar PV generation the heating can use that (which it can't if running at night) but secondly I like a silent house at night, and even the very low level hum of a quiet circulating pump is an annoyance to me, so it's off completely at night.

 

In our house during the overnight off period the house temperature won't drop by more than about 1 degree, so any set back operation is pointless.  That is really for old leaky houses to stop them getting too cold and then taking too long to heat up in the morning.

[PeterW]

Last one commissioned was a full slab install with reasonable levels of insulation (not Passive) and good airtightness and it’s purely on E7 and ASHP. 

 

DHW from 01:30 to 03:30 at 47c

UFH from 04:00 to 07:00 at 35c and room stat at 20.5c

 

Both get a boost from 18:00 to 19:00 and 19:00-20:00 respectively if needed. 

 

300 litre DHW tank gets boosted from 47c to 63c by E7 from 05:30 to 07:00 to give a lot of hot water. 

[newhome]

38 minutes ago, ProDave said:

so any set back operation is pointless.  That is really for old leaky houses to stop them getting too cold and then taking too long to heat up in the morning.

 

Surely set back in this context means that it simply stays switched off unless the heating was to drop so low it reached the set back temperature? It’s nigh on impossible for it to come on at the level I set it at - it might come on if I’m away in the winter and the system is set to away. I can’t easily switch my room stats off for specific periods so the set back process allows me to determine when they are off and on. 

[Redoctober]

6 hours ago, PeterW said:

Last one commissioned was a full slab install with reasonable levels of insulation (not Passive) and good airtightness and it’s purely on E7 and ASHP. 

DHW from 01:30 to 03:30 at 47c

UFH from 04:00 to 07:00 at 35c and room stat at 20.5c

 

This thread is an interesting one as we too are just coming to terms with our UFH and DHW systems, driven by an ASHP. Our individual room thermostats allow us to set the UFH to be called into action when the temperature drops below the level I have set them for, during particular periods of the day.

The Master panel, which I confess I never touch, shows me when the DWH is being called upon and also when the UFH is being called for. The main temp is set for 21c.

@PeterW - sorry for my ignorance but how can the UFH be set for 35c and the room stats at 20.5c. Would the UFH not will cut off in those rooms once the temp reaches 20.5c?

 

 

[Declan52]

1 minute ago, Redoctober said:

 

This thread is an interesting one as we too are just coming to terms with our UFH and DHW systems, driven by an ASHP. Our individual room thermostats allow us to set the UFH to be called into action when the temperature drops below the level I have set them for, during particular periods of the day.

The Master panel, which I confess I never touch, shows me when the DWH is being called upon and also when the UFH is being called for. The main temp is set for 21c.

@PeterW - sorry for my ignorance but how can the UFH be set for 35c and the room stats at 20.5c. Would the UFH not will cut off in those rooms once the temp reaches 20.5c?

 

 

He means the water being pumped round the ufh is set to 35c and the actual room stat is set to 20.5c.

[Redoctober]

3 minutes ago, Declan52 said:

He means the water being pumped round the ufh is set to 35c and the actual room stat is set to 20.5c.

Cheers - I appreciate that. ?

[PeterW]

As @Declan52 says, the blender is set to 35c so the ASHP CoP is better. 

[SteamyTea]

Best, and probably the quickest way to find out, us to do some tests, now is a good time as it is not too cold.

Should be able, over the next week, to find out how long it takes to increase the house temp by 1, 2, 3, and 4 K. And how much is lost during the night.

This does take a bit of effort, but it will give you both the heating and cooling curves. From them you can calculate just about everything.

Easier if you have a simple data logger, but a kitchen timer and a thermometer are good enough.

[vfrdave]

On 04/10/2019 at 14:54, Declan52 said:

I set my heating to come in at 6am when it is the time for it to come on most days, October to April depending on how cold it gets. So my boiler is fired up and heating my 350l tank. 

At 6:30 my programs for all my stats kick in. I have the living room, kitchen, sun room set to 21, the other rooms 20. If at 6:30 any stat is lower than the set temp then it will call for heat and start to warm up my slab. They will continue to call for heat until they get to whatever temp they need to be, usually takes around 60 mins before you would feel heat under your feet then maybe another 60 mins and it will have got to 20-21 and turned the demand for heat of.

The rest of the day the temp on the stats are set back so they don't call for heat unless it's really really cold as in -10 type weather. Then the next morning the cycle starts again. Some mornings depending on how cold it got during the night there might only be 1 zone or could be 5. 

So you are basically heating the slab up once in the morning, suits my family this time as the house feels warmer for kids going to school and me and the wife going to work, and then it will continue to heat the house after the stat has turned itself of for the rest of the day. 

This assumes that you have built your house to a high enough standard that it won't leak  like a tea bag. 

Big difference here your screed @Declan52 is traditional sand & cement and a big heat sink. @Ricco has cemfloor liquid screed probably 50mm deep, heats up quicker but loses it quicker also.

[Declan52]

3 minutes ago, vfrdave said:

Big difference here your screed @Declan52 is traditional sand & cement and a big heat sink. @Ricco has cemfloor liquid screed probably 50mm deep, heats up quicker but loses it quicker also.

And that is exactly the reason why I didn't go down the liquid screed route.

He can still set up roughly similar but his floor will reach temp quicker so won't need as much heat as mine but as you say will cool down quicker. So might need another blast of heat later on in the day depending on the heat loss of the house.

It's just trying to work out the best method that suits your own particular situation . It took me maybe 3 winters of adjusting different flow temps and boiler temps and room stats till I had it where I am now. It really is a case of trail and error until you get a setup you can live with.

[vfrdave]

2 minutes ago, Declan52 said:

And that is exactly the reason why I didn't go down the liquid screed route.

He can still set up roughly similar but his floor will reach temp quicker so won't need as much heat as mine but as you say will cool down quicker. So might need another blast of heat later on in the day depending on the heat loss of the house.

It's just trying to work out the best method that suits your own particular situation . It took me maybe 3 winters of adjusting different flow temps and boiler temps and room stats till I had it where I am now. It really is a case of trail and error until you get a setup you can live with.

I have all this ahead of me, hoping to move in within the next few weeks.

[Declan52]

Just now, vfrdave said:

I have all this ahead of me, hoping to move in within the next few weeks.

But your house will be damp and still drying out so you just need to get through the winter without costing a fortune.

[vfrdave]

2 minutes ago, Declan52 said:

But your house will be damp and still drying out so you just need to get through the winter without costing a fortune.

In normal circumstances yes, we have been pretty laid back and the place has dried out slowly over time. It has been 9 months since plastering finished, could have built another in that time.

[Declan52]

4 minutes ago, vfrdave said:

In normal circumstances yes, we have been pretty laid back and the place has dried out slowly over time. It has been 9 months since plastering finished, could have built another in that time.

Shouldn't be that bad then. What about the screed how long has it been down. 

[vfrdave]

14 minutes ago, Declan52 said:

Shouldn't be that bad then. What about the screed how long has it been down. 

Screed been in since late April so well dried out.

Edited October 13, 2019 by vfrdave
Typo

[Declan52]

Your laughing then.