Underfloor Heating excess Gas

[mar0507]

I have recently moved into a well insulated new build, with UFH downstairs and Radiators upstairs.  Previously i have been not so well insulated Victorian.

 

I have a Valliant EcoTec Pro 28 combi bolier, and Solfex UFH.

 

I am using roughly double the gas i ever have per day.

 

My Rads are set from 7am to 9pm to about 18 degrees.  My UFH is set from 6am to 9pm at 19deg, and then set back to 16 deg.

 

The UFH is set to 2 zones, the living area (all one room - approx 5.7 m x 5.26m) and then the hall and downstairs toilet.

 

My boiler temperature is set to 60 deg for heating and 55 deg form water.  The UFH return temp is set to 55 deg.

 

Why am i using so much more gas?  Solfex suggested the boiler be at 70 deg (but it made no difference).

 

Your help would be appreciated.  I understood UFH was so much cheaper to run.  Have i got something set wrong?  Could it be that the boiler is programmed wrong or it is plumbed incorrectly.

 

[SteamyTea]

14 minutes ago, mar0507 said:

I understood UFH was so much cheaper to run.

Not really.  A lot of it will depend on how well the floor is insulated under the pipes.

You may be just heating the ground under the house.

Your flow temperatures for the UFH seem high, and your timings seems short, it is more usual to have the UFH on permanently and at a lower temperature.

So it may be a mismatch there.

Also how much water are you heating, or is it a combi boiler?

[mar0507]

Thank you.

 

To be clear the boiler is a combi boiler.  Although the boiler is set to 60 deg, currently running at 54 deg (heating only).

 

The UFH takes roughly 1 hour per degree to heat up.

Just so i am clear, the UFH has one turn thing that you can set the temp, and it is at 55 deg (i looks like it is the return - but i am no expert).

 

So in the morning the UFH brings the zones back to 19 deg and will keep it that way until 9pm when i allow it to drop to 16 over night (Solfex, suggested this was good - and all the research i have done suggests best to drop it down a bit over night).  So how are the timing short?

 

I have been told by the developer (an individual - not Bovis and the like) that the insulating is very good - although to be fair unsure about the UFH insulation.  I will find out.  What is best for the UFH insulation?

 

Thanks again

 

[ProDave]

Are you saying your "well insulated new build" is using twice as much gas as your previous Victorian house?  That does not sound right.

 

Who built the new house and what can you tell us about it's construction and insulation?

 

At the end of the day the amount of gas will be pretty much the same regardless of the method of delivery, in fact UFH will waste some heating the ground under the house, but if it was done properly with enough under floor insulation, that wastage will be small,

[JFDIY]

And is the comparison like for like, have we gone from a mid-terrace to a detached house. Might be similar floor area, but different heat loads.

[Gone West]

2 hours ago, mar0507 said:

I understood UFH was so much cheaper to run.

Whoever told you that was wrong. UFH is more inefficient than radiators because even with a lot of insulation under the floor slab some heat will be lost to the ground.

[joe90]

1 hour ago, mar0507 said:

I have been told by the developer (an individual - not Bovis and the like) that the insulating is very good

He would, but how good is good. Most builders here build to way higher standards (more insulation and airtightness) than is the norm.

[PeterW]

2 hours ago, mar0507 said:

The UFH takes roughly 1 hour per degree to heat up.

Just so i am clear, the UFH has one turn thing that you can set the temp, and it is at 55 deg (i looks like it is the return - but i am no expert).

That’s too hot for UFH ! Turn it down ..!!

 

2 hours ago, mar0507 said:

 

I have been told by the developer (an individual - not Bovis and the like) that the insulating is very good - although to be fair unsure about the UFH insulation.  I will find out.  What is best for the UFH insulation?

If it is a new build then it will have to have met the 0.11 uValue target. Ask for the build up of the floor - also have you got your EPC/SAP certificate for the house ..?

 

I would also wonder at those temperatures if the boiler is getting into condensing mode so will be more inefficient and use more gas. 
 

I would be looking at reducing the flow temperature (both boiler and UFH) and adding a couple of hours to the run times. Also with gas you have no variable cost so also look at running it for 3 periods in the day - I can’t work out if you’re saying that it’s on permanent from 7am-9pm..?

 

The other issue will be the combi - how much hot water are you using ..? And did your old house use a tank or a combi boiler ..?

[mar0507]

Thank you for all your input.

 

firstly, UFH is not as cheap as radiators?  Even though every website you go to p, whether ufh or general sites, all say different.

 

with regards to the temperature, the ufh suppliers suggested the boiler at 70 degs would be better, and 55 degs for return, would be good.  So what is the better temperature for the boiler and return ( on ufh?). I have rads upstairs so they will need good heat I guess.  Therefore will they not take much longer to heat the room?  What is a good setting for my boiler for efficiency of cost, as well as for the system?

 

with regard to how much hot water are you using, there are 2 of us in the house, and have 1 shower each a day, and then general washing hands after toilet use etc.  The dishwasher and washing machine heat the water as it comes into the machine, so boiler not used.

 

to be very clear, the ufh thermostats are set to 19 degs between 6am and 9pm.  Then between 9 pm and 6 am they allow the room to drop to 16 degrees.  Again I was told this was better, by the ufh supplier (tech team).

 

in previous houses, with not as good insulation, we had radiators with one thermostat set to 19 degrees during the day, until about 9pm, then off, and back on about 7ish. The most we use was about 1.5 gas meter units per day (even in winter), but now we are up to about 3.  These older figures are both for combi boilers and those with water tanks.

 

the house previous to this the meter measured in cubic meters, and was not a combi boiler.  Very poor insulation, and still we used less gas than now.

Edited January 9, 2021 by mar0507
Give more info

[ProDave]

The chief advantages of UFH are no radiators to clog the rooms so you get "invisible heating" and very even heating with no pool of cold air at foot level so for a given temperature the room may feel warmer.  but UFH does lose some heat to the ground.  On the other hand stinking hot radiators on an outside wall (where they are usually placed) will lead to more heat loss through the wall locally so the 2 systems may ballance out a bit.

 

My suspicion is the insulation in the house may not be as good as claimed.  I see a number of houses in construction and they vary from the exceptionally good with everything detailed perfectly, these tend to be owner builders.  To the downright atrocious with lots of insulation thrown in, but literally thrown in with such poor detailing that there are air paths left to bypass the insulation and render it pretty ineffective. 

 

You really should have separate time controls for the radiator section and UFH section, with the UFH coming on earlier in the day to the radiators to account for the longer warm up time of the UFH.

 

A good measure of how well the building fabric is performing would be to heat up the house to a known measured temperature at the end of the day, then turn the heating off completely over night and see what the temperature has dropped to by the morning.

 

Set back temperatures on UFH are often used to counter the long warm up times and turn the UFH on again in the night if the temperature is dropping too far.  That really should not be needed in a well insulated house as it should not drop that much.

[JFDIY]

3m³ of gas is around 33kwh. Costing around £1. Doesn't seem bad to me during this cold snap. We're your other house readings at a similar outside temp?

 

Could the meter at your old place have been reading low?

 

Are they both meters in the same units?

 

 

[mar0507]

Hi again,

 

I am not sure about the previous houses.  but maybe the meters were reading wrong, and it might be the previous houses (except the one i have just left, which i know was cubic meters) was reading gas as cubic feet instead.

 

I have done some reading, around temperatures of condensing combi boilers, and they suggest the dew point is about 54 deg, and therefore the flow temp should be around 65 degrees, allowing for 20deg loss.  If this is the case, why should the flow temp be lower than 60deg - as as previously been suggested?  what is the best temp of the boiler to control both ufh and rads, and to be able to condese?

 

So during the cold snap should i keep the ufh at 19 (even during the night)?

 

I am sorry i am new to ufh and other people i know who have it say it takes a while to get used to, as it works different to normal rads.  

 

During this cold snap, the house drops 3 deg at night (from about 19 to 16 - even before i set the thermostats to the set back temp.)

 

Learning as i go.

 

 

[PeterW]

You cannot put water at 65°C into a UFH manifold - it will damage the floors.
 

You have an issue that as they rooms warm up, the delta between flow and return becomes less. As the blending valve reduces the amount of hot water entering the manifold, the boiler will start to short cycle and become significantly less efficient, which will increase your gas usage. The way to counter this is use a buffer tank but I expect there isn’t one as they regularly get missed out of designs. 
 

Is this a new build property ..? 
 

2 hours ago, mar0507 said:

firstly, UFH is not as cheap as radiators?  Even though every website you go to p, whether ufh or general sites, all say different.

Heat costs money, and based on the efficiency of the boiler it costs the same to heat a building with UFH as it does with radiators assuming the heat source is the same. So you house loses xkW/h through walls, floors, roof etc and your boiler puts in ykW/h to offset the losses. Whether that is putting in heat at 65°C into a radiator, or 40°C into UFH, the amount of heat required to raise the room temperatures is near as matters equal. UFH can’t make heat appear from nowhere, and the manufacturers know this. It’s the same argument they try with smart meters - you “save” because you use slightly less energy as you are more concious of it, and warm floors give the illusion that a room is warmer, so you switch the heating off sooner. In reality, the room isn’t as warm as if heated with radiators so you’ve “saved” by not heating the room to as high a temperature. 
 

 

[mar0507]

Quote

42 minutes ago, PeterW said:

The way to counter this is use a buffer tank but I expect there isn’t one as they regularly get missed out of designs. 

The solfex system we have has a mixer pack, in which the temperature twist was set to 55deg.  (I assumed this was a return, but seems more logical to be the temp to put into the ufh).  This twist thing has a range form 35 to 65 deg.

So if that is true, does this need to be set much lower.  What would you suggest?  The maker tech team said 55deg was right?

[PeterW]

Have you got any photos of this set up and a bit more detail ..?

 

Solid floor..?

Insulation levels..?

New build..? SAP/EPC score ..?

Size of floor heated ..?

Pipe Size ..?

Really need that sort of data to give a good idea as to where to go with this. 

 

 

 

 

[AliG]

4 hours ago, mar0507 said:

The most we use was about 1.5 gas meter units per day (even in winter), but now we are up to about 3.

 

Could part of the issue be that your old gas meter was imperial and the new one is metric.

 

1.5 units on a metric meter is 17kWh of gas. That is give or take 40p of gas. I very much doubt your old Victorian house only used 40p worth of gas for heating and hot water over a day in the winter. That would be the usage for just hot water.

 

However, 1.5 units on an imperial meter would be 47kWh, so more like £1.15 worth of gas. Could the old house have had an old imperial meter.

 

3 units of gas in a day in winter on a metric meter, i.e. 33kWh or 80p would be still a pretty small amount of gas to use on a cold day and a good result.

 

You should be able to tell from the conversion from units to kWh in your bill if the meters were different.

 

[JFDIY]

Another thought,bead the old house fitted with electric showers? And the new one with hot water off the combi boiler?  that may count for a reasonable shift in gas usage

[mar0507]

Thank you. 
 

My previous house, the units were definitely measured in cubic meters.  However, I lived there 6 months, so not during really cold weather, and although it did not have a combi boiler, I assumed the shower was from the tank, but maybe it wasn’t.  After all the hot water was instantl.  I just thought it was because the shower was immediately under the water tank.  The house prior to that, i don’t remember, and don’t now have the bills.  But again was a Victorian property.

 

the EPC rating of this new build house is B, and apparently the only reason it didn’t get an A was it does not have solar panels.

 

The measurements of the main zone are above, but to repeat are 5.7m x 5.26m.

 

The flooring is tiles .  I don’t know about the pipes etc.  Pic of ufh system attached.

 

Today the room heated to 19 after about 3 hours (from 16), a bit of sun caused it to get to 29, and only in the last 3 hours has it dropped to 19.

 

 

 

 

[AliG]

When you say you were using 1.5 units a day in the old house did you ever check that on a daily basis when it was cold?

 

You’d be surprised how much gas usage for heating goes up as it gets colder.

 

I use about 40000kWh a year for heating and 14000 for hot water.

 

So I average 150kWh a day.

 

However this is actually around 40kWh a day for 6 months when the heating never comes on. This rises to around 200kWh a day when the temperature falls to 6 or 7 degrees and over 300 kWh a day recently when the temperature has fallen below 0(it’s a big house) So if you have been using readings in the last few days when it has been about as cold as it gets nowadays then you will be using much more gas than normal.

 

If you are only using 3units in the coldest days of winter that seems like a pretty good result. That’s less than a pound on the coldest days of the year. Your gas bill would be under £500 a year.

 

It sounds like you were maybe using electricity for some hot water in the old place as really you’d expect to use that amount of gas just for hot water never mind heating.

 

 

Edited January 9, 2021 by AliG