Water based underfloor heating

neilrlsmith

Hi,

I have underfloor heating in my kitchen. The kitchen is about 36m squared so quite large. The floor is suspended concrete with tiling. Have done numerous tests with the gas meter reading I realise now that the floor represents 40% of my gas heating bill!!

So it's the age old question of timed v constant. We left the floor off for one day and it took almost 5 hours to get it back so not keen on totally off that's for sure as it would never be warm when we got up. Does anyone have any secret tips please

suki1964

neilrlsmith wrote: »

Hi,

I have underfloor heating in my kitchen. The kitchen is about 36m squared so quite large. The floor is suspended concrete with tiling. Have done numerous tests with the gas meter reading I realise now that the floor represents 40% of my gas heating bill!!

So it's the age old question of timed v constant. We left the floor off for one day and it took almost 5 hours to get it back so not keen on totally off that's for sure as it would never be warm when we got up. Does anyone have any secret tips please

Do you need the kitchen to be livable warm all day every day?

Most people only use their kitchens at meal times. and the heat of the cooking really helps warm a room

Maybe timing it so its on for the couple of hours in the morning before you get up and then a couple of hours in the evenings when dinner is being cooked and eaten

I only heat my kitchen like that

neilrlsmith

suki1964 wrote: »

Do you need the kitchen to be livable warm all day every day?

Most people only use their kitchens at meal times. and the heat of the cooking really helps warm a room

Maybe timing it so its on for the couple of hours in the morning before you get up and then a couple of hours in the evenings when dinner is being cooked and eaten

I only heat my kitchen like that

Thanks for responding. It's our main living area and we are in their most of the day as I work from home. But it's not that...if the floor goes cold during the day it takes ages to heat it up again. That seems expensive.

As a test I left it on 20 degrees over night and used up 3 units on the metre...

reeac

neilrlsmith wrote: »

Hi,

The floor is suspended concrete with tiling. Have done numerous tests with the gas meter reading I realise now that the floor represents 40% of my gas heating bill

Not that it helps you but I wonder how much heat is being lost downwards - depends upon what's below the suspended floor. Apart from that your useage is quite compatible with underfloor heating i.e. the room is used for many hours every day

suki1964

neilrlsmith wrote: »

Thanks for responding. It's our main living area and we are in their most of the day as I work from home. But it's not that...if the floor goes cold during the day it takes ages to heat it up again. That seems expensive.

As a test I left it on 20 degrees over night and used up 3 units on the metre...

Well you only called it a kitchen in your first post

I would say that would be around right for usage. I don't have uf heating but I know if I turn my rads off for a day it would take a day to reheat the house. So the rads come on for a couple of hours a day keeping the house at around 18oc.

Can you not get one of those thermostats fitted that you can set the temp for different times of day? 20 at night seems to be a waste. And surely you don't need it very warm when you are out and about

neilrlsmith

I can do that, yes. But my concern is the work the boiler needs to do to keep getting back from the lower night/out temperature...

reeac

neilrlsmith wrote: »

I can do that, yes. But my concern is the work the boiler needs to do to keep getting back from the lower night/out temperature...

This has been covered before. You will always save fuel by switching off the heating and then later on switching on again. The reason is that heat loss from a building is proportional to temp. difference between inside and outside. By switching off you are allowing the inside temp. to drop, thus reducing temp. differential and so the rate of heat loss. Actually, as underfloor heating has so much thermal mass [inertia] that it reduces the rate of cooling off once switched off and thus keeps the inside/outside temp. differential and hence the heat loss high.

I think that your best bet, if you use the room for many hours per day, is to use the inertia effect by switching off in early evening [say 2000] and then back on at maybe 0300-0400. - all depending on when you go to bed and get up.

neilrlsmith

so off only between 8pm and 3am. I can set a maximum fall back temp which I dont want to be too low as it'll struggle to get back up again. I am taking daily readings but on constantly is taking up about 6 units per day which is ok. I'll try 23 during 3am to 8pm and then set a fallback temp. of 18 from 8pm to 3am and see what the reading is then.

Thanks again.

reeac

neilrlsmith wrote: »

so off only between 8pm and 3am. I can set a maximum fall back temp which I dont want to be too low as it'll struggle to get back up again. I am taking daily readings but on constantly is taking up about 6 units per day which is ok. I'll try 23 during 3am to 8pm and then set a fallback temp. of 18 from 8pm to 3am and see what the reading is then.

Thanks again.

What I've said is based on theory so I'm glad that you're going to do some experiments. Please let us know the results.

Pincher

The UFH temperature is restricted by a separate thermostatic mixer. When you are heating up from cold, you might get 70 degrees from the boiler, because the boiler thinks the house is too cold and needs to go full blast, but only some of the boiler output is mixed with the UFH loop, with the rest "rejected" because it's TOO HOT. The consequence you get NO CONDENSATION.

My Glowworm setup is geared towards temperature maintenance, with weather compensation as well, so there is no need to go full blast. The boiler output is around 50 degrees C, so the UFH mixer won't reject most of it. The returning water is cooler, so condensation happens most of the time.

When it's 0 degrees outside, like today, I spend £10~£12 on gas a day, maintaining 20 degrees, for a 5 bed semi, which is about right. When you say 40% is spent on the kitchen UFH with everything else switched off, you are still heating the rest of the house, because heat spreads and rises. If the overall heating cost is about right for your house, I wouldn't worry about it.

My kitchen floor gets toasty in 30 minutes, and I can definitely feel it through socks. We dug up the concrete, put in 100mm of Kingspan, pegged the pipes directly on the Kingspan, then about 30mm of scree (cement), then glue and tiles. Only exposed floor area have UFH, not under kitchen units, and CERTAINLY not under the freezer. So in a 14m2 kitchen, only 7m2 of UFH.

1. Is the thermostatic mixer temperature set TOO LOW?

2. Is the UFH pump speed set to LOW (I/II/III)?

3. Pipe run too long. maximum length 100 meter per loop.

For a double bedroom, of 24m2, we needed two loops. For 32m2, I would expect you have three loops.

My kitchen floor does not actually use a separate pump.
The length of the pipe introduces quite a lot of resistance, such that the flow is relatively slow, so that the exit end of the floor is noticeably cooler than the entry end. I have a wall TRV (high mounted, not near ground level, which will pickup the heat from the floor and close the valve prematurely) which allows me to control the flow, but I leave it on maximum, because the flow is slow enough already.

4. Insufficient insulation, so you are heating the concrete first.

My floor cools down in 30 minutes, because the scree is the only thermal mass. If yours takes hours to cool down, I suspect the entire "suspended concrete floor" is the thermal mass.

highrisklowreturn

Buy a superser. Pay £17 for a bottle which last 2-3weeks Problem solved.

I don't even understand why people pay for central heating - if I had a new build I would keep it totally out, have a stove, superser, and an electric feed to the bathroom water - or spend thousands on a system that might need replaced, swapped between oil and gas, develop leaks in hard to reach places, rust, get gunked up and 'need' 'power flushed' every time a radiator won't heat.

How people heat their houses today is mental - 100 years ago people would have 10 kids and have them around one or two house fires and that would do it.