UFH system lots of help required

[zoe61]

I have read all the online information but struggling to get any good honest impartial reviews. We have a two story house that is built into a hillside and we are also using the attic as our living space. Its a conversion project but a fairly modern building so it has a 100mm cavity with 50mm insulation. We plan to further insulate the house so i was thinking of adding at least 50mm insulation to the inside of the house and then plaster board on top of that. This opens its own can of worms of questions (how will we do this, will this mean we need MHVR system, will it be enough/not enough insulation etc.).

 

The ground floor of the house is a concrete slab with 3 walls solid filled with concrete due to the house being built into a hillside. I will obviously be using screed for this floor with 120mm floor insulation and 100mm insulation of the sold will walls, and 50mm insulation on the exposed wall. Approximately 50% of the front wall is glass. 50% of the floor will be tiled and the rest carpet. My concern with this floor is will it be warm enough with the UFH alone if we have a cold winter like last year?

 

I'm now stuck with the rest of the house. We have metal web floor joists so can either go for spreader plates or screed. All of the floors will be carpet. I've heard some people say that the UFH doesn't work well with carpet and as soon as you turn the system off its cold, therefore making it expensive to run. So should I go for radiators or wet UFH?

 

If I go for UFH would I also need it in the attic (large area roughly 12m x 5m) or would it be a waste of money?

[MikeSharp01]

1 minute ago, zoe61 said:

This opens its own can of worms of questions (how will we do this, will this mean we need MHVR system, will it be enough/not enough insulation etc.).

You probably only need, or rather one will only be valuable, an MVHR if you can make the building air tight so all the air is extracted and replaced via the MVHR. Plastering is good at creating air tight walls but you need to take this round to the windows, doors, boiler vents, services entry / exit points - essentially any holes in the building.

 

Putting insulation on the inside has challenges as well because you need to ensure that no moisture in the form of condensation occurs where you get warm air at one temperature hitting colder surfaces at another, it is called dew point. There is loads out there on this to help and probably some robust detailing to allow you to see how this might be done. If you want to go all the way then there is a passive house standard for retrofit / refurb it is called the EnerPHit standard for energy consumption, insulation and air tightness.

 

Not sure on the UFH questions although I would not have thought having it in the attic of a well insulated house would be worth it and we are not having it upstairs either rather relying on the main slab to warm the whole house through.

[Temp]

We have UFH on two floors. My view is that it works well for families that have one person at home in the daytime. If you are both working 9-5 then it's possible rads are a better option. 

 

UFH does work with carpet but I strongly recommend you use the special low TOG underlay (circa 0.6-0.7) and keep the overall TOG value as low as possible (ideally 2.0, max 2.5). If you walk into a carpet shop and they tell you all of their carpet and underlay is suitable for UFH then they don't understand the issue. Usually they will have to go and look up the manufacturers information to find the TOG. Beware as they may come back with made up numbers. One chap tried to tell me the TOG of a carpet we were looking at was 10 - like a reasonable duvet.

 

When you have found your carpet and place an order watch out for the small print. One said something like... "Many of our carpets come in two versions, either hessian or rubber backed, we reserve the right to supply either version". The hessian version will have a much lower TOG than the rubber version but won't feel as soft under foot. Try out the carpet and underlay combo in the store to see if it feels right. Make sure you get exactly that combo on the order and delivered. If you find a good carpet salesman he will understand a lot of the above.

 

If the TOG is too high you might be able to crank up the temperature of the UFH to push heat through it but that can effect the performance of a heat pump or oil boiler (to lesser extent). Worse case you crank up the flow temperature and the temperature of the return to the boiler gets too hot for the boiler to work in condensing mode.

 

Edited September 28, 2018 by Temp

[Temp]

We also have MVHR and our house isn't perfectly air tight. Not least because we have two wood burning stoves. They have glass doors but aren't totally room sealed types, they burn room air. So we probably loose some benefit of the MVHR heat recovery but the constant ventilation provided is great. Clothes dry faster on racks, air feels fresher. Wouldn't be without it now.

[A_L]

When you mention insulation give the type, it makes a lot of difference to the thermal qualities and as Mike has mentioned other characteristics.

You do not mention insulation of the attic ceiling, insulating to U=0.15 is a must. The solid walls, have they any insulation? particularly those which presumably are only partially embedded in the hillside? 50mm of insulation is not enough for the exposed wall, 100mm of insulation of conductivity (k/lambda) less than 0.03 would be better.

What direction is the window and single/double/triple glazed?

The ground floor should be O.K. with UFH in screed as long as window at least double glazed. As for the attic, if only for occasional bedroom use consider radiators on a separate zone here if you are not using a heat pump for CH.

As regards MVHR you need to get total uncontrolled ventilation below about 3m³/m²(external area)/hr to benefit.

1 hour ago, zoe61 said:

I've heard some people say that the UFH doesn't work well with carpet and as soon as you turn the system off its cold, therefore making it expensive to run.

As explained by Temp above carpet acts as an insulator but you can increase the flow temperature as long as the surface temp does not exceed 27/28°C. It gets cold quickly because there is little storage of heat in a lightweight floor. It does not affect the fuel bill which is determined by heat losses.

[Dudda]

You've a few questions which ask more questions. 

First with the 100mm cavity that's only half filled you could look to fill the remaining 50mm with beads. This would be cheaper, easier and a lot less disruptive than drylining internally. Secondly what's the outside of the house like? Would you consider external insulation? You can then go 100 or 150mm insulation, it will reduce cold bridges, reduce internal condensation risk, give a new fresh look to the house and not reduce internal floor areas. You can continue to live in a house when external insulation is added.

 

On the ground floor you plan on using a screed and 120mm of insulation. Is this on top of the existing concrete slab? What's there currently as adding this additional height will reduce your floor to ceiling height and potentially change all the door thresholds. Are the doors and windows high enough to accommodate this?

 

On upper levels screed generally works better than spreader plates but it's heavier. The temperature is more controlled and slowly released with screed. You've to make sure the existing floor can support the weight of the screed.

 

If you've only 50mm insulation in the cavity and go the internal insulation route with 50mm you'll probably need heating in the attic as you'll have a fairly high heat loss. It's not a super insulated house where the heat rises into the attic. If you fill the cavity and externally insulation with another 100 or more and have good airtightness you can look at not heating the attic.

[Ed Davies]

21 minutes ago, Temp said:

Beware as they may come back with made up numbers. One chap tried to tell me the TOG of a carpet we were looking at was 10 - like a reasonable duvet.

 

Possibly confusion rather than made up as such: 1 tog [¹] is a thermal resistance of 0.1 m²·K/W so a thermal conductance (“U-value”) of 10 W/m²·K. Maybe that was what was on the manufacturer's brochure/catalogue/data sheet.

 

Since that's about the thermal resistance/conductance of the slab/air interface anyway it would be reasonable to think of a 1 tog carpet as doubling the required slab/air temperature difference, a 2 tog carpet as tripling it, etc.

 

[¹] lower case, it's just the name of the unit (slightly humorous, as in getting “togged up”) , not an initialism.

[zoe61]

1 hour ago, MikeSharp01 said:

Putting insulation on the inside has challenges as well because you need to ensure that no moisture in the form of condensation occurs where you get warm air at one temperature hitting colder surfaces at another, it is called dew point. There is loads out there on this to help and probably some robust detailing to allow you to see how this might be done. If you want to go all the way then there is a passive house standard for retrofit / refurb it is called the EnerPHit standard for energy consumption, insulation and air tightness.

 

 

Thank you Mike. In terms of the cavity walls will adding insulation still present a problem in terms of condensation? Researched this and struggled to find any answers for cavity walls. In my mind its no different to adding plasterboard to the walls and therefore shouldn't pose a problem?

[zoe61]

1 hour ago, Temp said:

We have UFH on two floors. My view is that it works well for families that have one person at home in the daytime. If you are both working 9-5 then it's possible rads are a better option. 

 

 

 

We currently work all day, but when we have children things will no doubt change. Do you say this because of the warm up times for UFH? 

[zoe61]

43 minutes ago, A_L said:

When you mention insulation give the type, it makes a lot of difference to the thermal qualities and as Mike has mentioned other characteristics.

You do not mention insulation of the attic ceiling, insulating to U=0.15 is a must. The solid walls, have they any insulation? particularly those which presumably are only partially embedded in the hillside? 50mm of insulation is not enough for the exposed wall, 100mm of insulation of conductivity (k/lambda) less than 0.03 would be better.

What direction is the window and single/double/triple glazed?

The ground floor should be O.K. with UFH in screed as long as window at least double glazed. As for the attic, if only for occasional bedroom use consider radiators on a separate zone here if you are not using a heat pump for CH.

As regards MVHR you need to get total uncontrolled ventilation below about 3m³/m²(external area)/hr to benefit.

As explained by Temp above carpet acts as an insulator but you can increase the flow temperature as long as the surface temp does not exceed 27/28°C. It gets cold quickly because there is little storage of heat in a lightweight floor. It does not affect the fuel bill which is determined by heat losses.

Cavity walls= 50mm foil backed kingspan

Hillside walls= 100mm internal kingspan

When I say 50mm insulation, these walls all have 50mm in the cavity and another 50mm internally.

In terms of attic I havent quite got there yet to determine whats going in, but we have taken the roof off and a new one is going on so we can do what we want here.

 

Windows are South-West facing (will get a lot of wind) and double glazed aluminium.

 

In terms of the MVHR, obviously its easier to fit this prior to testing the house for air tightness, is there a way to determine before hand if we will achieve the values you state please?

[zoe61]

1 hour ago, Dudda said:

You've a few questions which ask more questions. 

First with the 100mm cavity that's only half filled you could look to fill the remaining 50mm with beads. This would be cheaper, easier and a lot less disruptive than drylining internally. Secondly what's the outside of the house like? Would you consider external insulation? You can then go 100 or 150mm insulation, it will reduce cold bridges, reduce internal condensation risk, give a new fresh look to the house and not reduce internal floor areas. You can continue to live in a house when external insulation is added.

 

On the ground floor you plan on using a screed and 120mm of insulation. Is this on top of the existing concrete slab? What's there currently as adding this additional height will reduce your floor to ceiling height and potentially change all the door thresholds. Are the doors and windows high enough to accommodate this?

 

On upper levels screed generally works better than spreader plates but it's heavier. The temperature is more controlled and slowly released with screed. You've to make sure the existing floor can support the weight of the screed.

 

If you've only 50mm insulation in the cavity and go the internal insulation route with 50mm you'll probably need heating in the attic as you'll have a fairly high heat loss. It's not a super insulated house where the heat rises into the attic. If you fill the cavity and externally insulation with another 100 or more and have good airtightness you can look at not heating the attic.

Thanks Dudda. Externally the house is reclaimed stone so do not want to cover this. In terms of ceiling heights this isn't a issue the ground floor will have a ceiling height of 2.5m after all the insulation and screed, and the other floors are also generous. Not fussed about loosing wall space either as large rooms.  

 

Floor joists are all at 400mm centres and can take a screed load. 

 

It seems like I definitely need to heat all floors, I just need to decide upon the extent of UFH. 

[MikeSharp01]

1 hour ago, zoe61 said:

Thank you Mike. In terms of the cavity walls will adding insulation still present a problem in terms of condensation? Researched this and struggled to find any answers for cavity walls. In my mind its no different to adding plasterboard to the walls and therefore shouldn't pose a problem?

Its all about the temperature gradient across the layers and the spaces, if any, between the layers. Its a pain but there is a bit of software call wufi that will model it for you but your probably need to be an expert, I dabble but am no expert, to use it. I found that the company selling me the insulation would model it for me. I just sent them - can't recall who, the build up and they told me it would or would no work including the likely dew point opportunities given our weather.

[Declan52]

Don't think of mhrv as just a means of saving you some heat. It's main bonus is the fresh clean air you have in your house. No stuffy rooms etc. If it also saves a bit of heat from escaping then happy days.

By the sounds of it the way you are stripping the house back and filling every hole your already on your way to reducing your air leakage so might not be far away from a blower test of below 5 maybe even 3.

[PeterW]

If you already have some cavity insulation then the chances of condensation with an additional layer internally are significantly diminished. Oddly, the basement will suffer less with heat loss so is less of an issue 

[A_L]

2 hours ago, zoe61 said:

In terms of the MVHR, obviously its easier to fit this prior to testing the house for air tightness, is there a way to determine before hand if we will achieve the values you state please?

 

The short answer is no, but with much of the house buried in ground it should be possible. The joists of the first storey floor and ceiling are likely to major contributors to air leakage if they penetrate the inner leaf of the cavity wall, taping membrane to them is a laborious and finicky job, with the roof off there may be opportunities to place membrane advantageously. All Kingspan will have to have taped joins. If modifying window reveals, adding insulation to reduce thermal bridging, it should be possible to tape windows to reveals. 

[Temp]

4 hours ago, zoe61 said:

We currently work all day, but when we have children things will no doubt change. Do you say this because of the warm up times for UFH? 

 

Yes.

 

Lot depends how well insulated your house is. If your house is badly insulated then it makes more sense to turn off or up and down  when there is nobody home or at night. If it's very well insulated then it's not costing you much to leave it on 21C all the time.

 

Our house was built about 11 years ago to slightly better than building regs standards. We program our UFH to drop the temperature at night by about 3 degrees (aka "set back"). This means that most nights the heating is off unless it gets very cold outside. However it can take 90mins to get back to "normal" temperature. So when we are getting up at 6am the heating is programmed to start rewarming the house at perhaps 4.30am. With rads 5.30 would probably have been ok.

 

Most days there is someone at home but if we both leave at say 7.30am the heat we have put into the floor slab dissipates over the next few hours when there is nobody there. As I said it's not quite so bad for us because there is someone at home most days.
 

 

[newhome]

2 hours ago, Temp said:

Our house was built about 11 years ago to slightly better than building regs standards. We program our UFH to drop the temperature at night by about 3 degrees (aka "set back"). This means that most nights the heating is off unless it gets very cold outside. However it can take 90mins to get back to "normal" temperature. So when we are getting up at 6am the heating is programmed to start rewarming the house at perhaps 4.30am. With rads 5.30 would probably have been ok.

 

Thanks for this info @Temp it is helpful to me too. Now that my heating is finally working I want to try to work out a plan for the set back temperatures and time to heat back up. I had expected it to take about 90 minutes to get back up to temperature but have only dropped the temperature by 2 degrees during set back so maybe I should look at upping that to 3 degrees. Out of interest how much insulation do you have in the floor? I wish I had more. The TF company designed it with much better than building regs standard in the walls but there is only the minimum (50mm) in the floors sadly. It was built to 2006 regs. Do you put the set back temperature right down if there is no one there during the day? I have again set mine to 2 degrees lower during that time and then 90 minutes before I am due to arrive home it kicks back up to 20 degrees downstairs, 18 degrees upstairs but maybe set back should be lower. It's all theory at present because the weather has been weirdly warm here for this time of year and I haven't switched it on yet. 

[ProDave]

Even in 2003 we put 150mm of floor insulation, and that was possibly not really enough for UFH.

 

In our new house I am setting it up for the heating to run all day (it is on a conventional programmer so easy to change) but off at night.  The driving force for that is to try and do the heating only in the daytime so when we eventually get solar PV then self usage is easier.  The house does not cool down quickly so that should not be an issue.

 

I have however been instructed to start the upstairs (bathrooms only) UFH early in the morning so one gets warm feet for ones morning ablutions.

[Temp]

On ‎28‎/‎09‎/‎2018 at 18:39, newhome said:

Out of interest how much insulation do you have in the floor? I wish I had more.

 

We have about 50mm PIR+30mm EPS. Also wish we had more.

[Temp]

On ‎28‎/‎09‎/‎2018 at 18:39, newhome said:

Do you put the set back temperature right down if there is no one there during the day?

 

We typically nudge it down to say 16-17C when going out.

 

We have stats in each room and they are all set different. Even if there is someone home the default is more like 18-19C in the daytime rising to 21-22 in the early evening and weekend.  Depends how active we/you are when home.

[newhome]

11 minutes ago, Temp said:

 

We typically nudge it down to say 16-17C when going out.

 

We have stats in each room and they are all set different. Even if there is someone home the default is more like 18-19C in the daytime rising to 21-22 in the early evening and weekend.  Depends how active we/you are when home.

 

Thanks, that's useful. I have separate stats in each room too and only intend to set the rooms I actually use to a decent temperature as there are quite a few rooms that I don't use unless there are visitors here. I did have all of the non used rooms set to 16 earlier in the year (the ufh actually only worked for a month before it was switched off for the summer) but I think that's probably a waste so intend to have those rooms on frost setting this winter. 

 

I think I'll put the set back temp to 16 when I'm not around. That way I can see how low it drops and how long it takes to heat back up to 20 and play around with it from there. I work from home some days so am not exactly rushing about then so will want it warmer . Time to have a play with it. It is 19 degrees in the main living space today without the heating on as things like the tumble dryer etc tend to keep the temperature up a bit even without the heating on at this time of year. I can see me needing it on soon though as it's getting colder outside. 

 

 

 

 

 

[Temp]

Our stats have been off all summer but this weekend we decided to turn on the bathroom and living room stats they could call for heat if needed. They both came on first thing today so it must have been below 18C in the living room overnight. 

[newhome]

My living room was 17.6C at 6am this morning so would have come on overnight had the heating been switched on. 

[Jeremy Harris]

Our place was at 20.5 deg C first thing this morning, and rose to a bit over 21 deg C through the day.  Heating hasn't come on since last winter, and I doubt it'll need to come on for a few weeks yet.  Last winter the heating was on for a total of around 250 hours, spread over about 4 months or so.  There were lots of days in December, January and February where the heating didn't need to come on at all, as the couple of hours of heat dumped into the slab the day before was enough to keep the house at over 20 deg C.

[newhome]

I put the heating on tonight, just in 2 rooms for now. It was 17.1 in here when I got home and an hour and a half later it's still only 18.5 . The boiler has gone off at least but not before thumping out 24 kw.