Underfloor heating: how to use properly

Spir4

Hello everyone,

I've recently moved to a flat that has underfloor heating in every room, and no wall hanging radiators. The past month we've had some pretty cold days and I feel like I haven't been utilising the system properly, so I hope other people with only UFH have got some tips and tricks for me.
The other components of my heating system are a timeswitch programmer in the utility room, and a thermostat in every room. I can program 3 different on-off schemes per day on the programmer, and the thermostats are basic models where you can only set the temperature. When it's one degree colder than the set temperature it starts to ask for heat, and when it's one degree warmer than the set temperature it stops asking for heat.

I've noticed it takes remarkably longer for the UFH to heat up the flat, easily 2 hours (compared to my previous flat with wall hanging radiators). You'll feel the floors getting warm pretty quickly, but that hasn't heated the flat yet obviously.

How do you set your programmers and thermostats?

Thanks!

Gerry1

Is it a simple wired electric system, or a 'wet' system with pipework?

If it's the former, it'll bankrupt you... 

Spir4

Gerry1 said:

Is it a simple wired electric system, or a 'wet' system with pipework?

If it's the former, it'll bankrupt you... 

Well lucky for me then, it's a wet system with pipework

Gerry1

How it is powered?

Spir4

Gerry1 said:

How it is powered?

The building has a central heating plant/network in the basement which transports the hot water to every flat depending on the demands of the flat. There's a prepayment meter in every flat that you have to topup for this.

matelodave

Depending on how your underfloor system has been installed will affect the time it takes to heat or reheat your flat. Overlay or infloor.

Most u'f systems are installed in the floor slab and then fully screeded over, so they act like storage heating. They also usually run at significantly lower flow temperatures than a radiator system both of which mean that they work best when run for a lot longer. They dont really lend themselves to short sharp heating cycles like a high temperature radiator installation.

Ideally you turn the stats down several degrees overnight or during the day rather than off, and up again when you want the room up to temperature to avoid the place getting stone cold. This is a lot easier to do with programmable stats but it does avoid the long heating times.

The best thing about underfloor systems is that you can usually set the room stats down a few degrees lower than a radiator system because you have heat all over coming up from floor level and any draughts are warm. Even my wife who's the archetypal "chilly mortal" is happy at around 19 degrees

Think like you are driving a car - cruising along at 50mph will take a bit longer to get to your destination but will give you much better fuel consumption than thrashing along at 75 and slowing/speeding up with the traffic.

You need to experiment a bit with nudging the temps downwards and seeing what you can get away with without being cold and working out how long it takes to reheat. Hopefully your energy meter can display consumption in kwh so you can monitor what happens when you tweak settings. Always give it a couple of days to settle between tweaks as u/f systems are pretty slow to respond.

lohr500

Do you know what you are paying for with the pre-payment meter? Is it based on the consumption of hot water for your flat?
I wonder how it is measured? Such a concept is new to me and I am interested in how it works.
Are you sure you are not contributing to a flat wide scheme, where potentially you are disadvantaged by minimising your own heat usage?

Spir4

lohr500 said:

Do you know what you are paying for with the pre-payment meter? Is it based on the consumption of hot water for your flat?
I wonder how it is measured? Such a concept is new to me and I am interested in how it works.
Are you sure you are not contributing to a flat wide scheme, where potentially you are disadvantaged by minimising your own heat usage?

Yes it's based on the consumption of hot water. In the summer it's about £1 a day (the standing charge is about £0.80), but when the heating is on a let's say 6h a day, it's about £5 a day.
This is how it works:

Spir4

matelodave said:

Depending on how your underfloor system has been installed will affect the time it takes to heat or reheat your flat. Overlay or infloor.

Most u'f systems are installed in the floor slab and then fully screeded over, so they act like storage heating. They also usually run at significantly lower flow temperatures than a radiator system both of which mean that they work best when run for a lot longer. They dont really lend themselves to short sharp heating cycles like a high temperature radiator installation.

Ideally you turn the stats down several degrees overnight or during the day rather than off, and up again when you want the room up to temperature to avoid the place getting stone cold. This is a lot easier to do with programmable stats but it does avoid the long heating times.

The best thing about underfloor systems is that you can usually set the room stats down a few degrees lower than a radiator system because you have heat all over coming up from floor level and any draughts are warm. Even my wife who's the archetypal "chilly mortal" is happy at around 19 degrees

Think like you are driving a car - cruising along at 50mph will take a bit longer to get to your destination but will give you much better fuel consumption than thrashing along at 75 and slowing/speeding up with the traffic.

You need to experiment a bit with nudging the temps downwards and seeing what you can get away with without being cold and working out how long it takes to reheat. Hopefully your energy meter can display consumption in kwh so you can monitor what happens when you tweak settings. Always give it a couple of days to settle between tweaks as u/f systems are pretty slow to respond.

One of the problems is that the flat has floor to ceiling windows, and is south facing. So in the winter, when the sun is shining, the temperature in the flat goes up to 27 degrees. So what happens is that up until let's say 9am, the heating is on because of a cold night. Then the sun starts the heating process and all of sudden it's 27 degrees in the flat, the stats stop asking for heat, but since it's UFH the whole floor keeps heating for another hour or so after the heating has switched off. So it gets even warmer, up until the point we have to open the windows to make it bearable. Which is an absolute waste.

So what I thought we'd need are smart stats. Then I can probably set schedules that depend on the forecasted weather. Or I'd have more than 3 schedules per day so I could let the UFH come on for an hour, every two hours or something.

70sbudgie

I only have underfloor heating in two rooms, the kitchen and main bedroom. Both rooms have their own programmable thermostats. The way I use my UFH is that I have it on for a few hours before I want it warm and then turn it down significantly and just enjoy the residual heat.

In the kitchen, this means early morning so it is nearly at temperature when we all come down for breakfast. If we have a late morning and don't come down till after the stat has reduced, the kitchen is still warm from the residual heat. The kitchen has a concrete floor, so the residual heat from the morning keeps the kitchen warm all day and by not heating past about 9am, the kitchen isn't too warm from cooking. If we have an early morning, the floor can feel warm before the air is. On the rare occaision we are up really early, we just lump it! (We're usually miserable anyway as we're not morning people!)

In the bedroom, the UFH comes on early evening and switches off at my aspirational bedtime, so it is warm to go to bed. I've realised that I quite like sleeping in a cooler room with heavier blankets, so I don't have the stat high in the morning. 

My cool temperatures are 15.5°C, the kitchen warm temp is 17.5°C and the bedroom is 19°C. 

It probably took me a couple years of tweaking to work out how best to get the UFH to match our routine.

pensionpawn

Gerry1 said:

Is it a simple wired electric system, or a 'wet' system with pipework?

If it's the former, it'll bankrupt you... 

I have around 7.5 kWs of UFH across three ground floor rooms of my 4 bed detached. The highest cost during this cold snap was around £3.30 / day. However I only have UFH because I have stone floors, E7 and I have 7.12 kWs of solar panels to offset the cost Sep - Nov & Feb - Apr. It's off May - Aug inc. The best way to run it is to set it up to boost in the last hour of E7 and then set it to the lowest temp (19.5c for me) to keep the floors neutral in temp.