UFH in a Passive House

[hejdavies]

Hi all,

 

about to embark on self-build project. We have plot and planning. The layout optimises solar gain so I am keen to achieve passive house standard. 

 

I have noticed on this forum that many self-builders seem to include UFH in their passive house build but I have been told this is simply not necessary... So i'd be grateful for thoughts on this please!

[PeterW]

Welcome ..!

 

have a look at @JSHarris blog and the benefit of ufh in a house with a low heat requirement. It’s useful to move heat about the slab from warm areas to cool areas without having to inject heat from an external source. 

[joe90]

Even in a passive house a small amount of heat is required and UFH is a more comfortable way to heat, requires lower water temps ( so ideal for ASHP), I have UFH on the ground floor ( as one zone) and no heating upstairs apart from towel rads in the bathrooms and electric UFH in our en suite. My theory ( as we are yet to move in and try it out?) is that if upstairs gets a little cold in the middle of winter a couple of portable electric heaters are more than suffice.

 

cross posted with Peter, yes I have installed a separate pump on the UFH manifold so I can shift heat about without firing up the ASHP. we are facing south so should get solar gain.

Edited April 18, 2018 by joe90

[Gone West]

49 minutes ago, hejdavies said:

I have noticed on this forum that many self-builders seem to include UFH in their passive house build but I have been told this is simply not necessary... So i'd be grateful for thoughts on this please!

 

It isn't necessary if the PH has a very low space heating requirement. We decided against needing wet UFH with the resultant saving in UFH heat source, pipework, manifolds, valves etc. If the space heating requirement is low enough it can be supplied by warm air through the ventilation system. We use a Genvex Combi 185 for our ventilation, warm air heating and DHW. The warm air heating and DHW is supplied by a 500W EASHP.

[ragg987]

Me too! Based on @JSHarris postings I also added a passive circulator in my UFH. It is difficult to say exactly how effective this is, but I believe it lets our basement receive some heat from e.g. solar gain upstairs. Or the reverse, makes upstairs a bit cooler on very hot days.

 

Note that if you build to PH standards and have a lot of solar gain you risk over-heating in the summer. Suggest you get this analysed. Solar gain will only work as a substitute for input heat if we have any sun. If last winter is anything to go by, these ar not so many.

 

As @joe90 says, PH does not mean you need no heat, just that you need less of it. So yes UFH is not needed, you can simply add e.g. heating into your MVHR or a few well-placed radiators. We add heat into our MVHR upstairs, no UFH.

[Dudda]

Welcome. The underfloor heating requirement totally depends on your house and to an extent your preferences. You definitely don’t have to have it and we can only give general advice with regard to UFH on comfort, how it can be used for cooling, etc without knowing more about your plans and proposed specification and insulation.

 

If you want to achieve Passive House Standard you need someone to prepare a PHPP file for you. As you already have planning permission its critical this is done as soon as possible as it could alter some of the design. If not already done I’d start and get this carried out as this will inform you exactly what is required in terms of heating, cooling, etc and therefore if UFH is suitable or required.
 

[hejdavies]

The layout is optimised for solar gain and we expect to meet the PH standard (space heating demand 15kWh/m2/yr). we have outline planning and are getting together detailed plans. We are thinking polished concrete floor in kitchen area and tiles in bathroom so i was wondering whether UFH was necessary to increase comfort on colder days etc. but i dont particularly want to spend money on something which we may never need... how much would you expect a UFH to cost/m2 ... and i was thinking an ASHP would suffice for DHW??

[jack]

Welcome to Buildhub.

 

We have Passivhaus-level insulation and airtightness, with UFH in the downstairs slab.

 

Our ASHP broke down at the start of winter. We found that a simple 2kW electric column heater with a fan on it was able to keep the house comfortable (if not exactly toasty) throughout the whole of winter. We usually ran it on low, bumping it up to the full 2kW during cold snaps.

 

6 minutes ago, hejdavies said:

We are thinking polished concrete floor in kitchen area and tiles in bathroom so i was wondering whether UFH was necessary to increase comfort on colder days etc. 

 

We have polished concrete floors throughout the downstairs area. It wasn't comfortable to walk on barefoot when the UFH wasn't working this winter. A decent pair of socks was okay for me, but it was certainly a lot more comfortable when the UFH was working the previous winter! 

 

Bear in mind the UFH in a PH dwelling will run - and indeed, will have to run - at a much lower temperature than in a standard building regs house. We have our ASHP output water on the absolute lowest heat setting, which is 25C. That works fine. 

 

Also, don't let anyone tell you that you don't need heating in your bathrooms in a house with Passivhaus levels of insulation. We were convinced not to include it and it's one of the larger regrets I have about our build. We're now retrofitting IR panel heaters, but I'd have preferred UFH.

 

You should also think ahead early to how you've going to control solar gain, especially in the shoulder months where the sun is lower in the sky (so can get deeper into the building) and it may still be warm. 

 

One other consideration: you may not be thinking of it now, but one day you may need to sell. I think you'll put a lot of potential buyers off if you don't have UFH or at least beefy-looking central heating. You know you don't need the latter, but a lot of buyers won't know, and won't be convinced just by your say-so.

[joe90]

There are some who use direct electric heating for UFH and I have heard of one person ( not on this forum) that uses an electric radiator heating element for his UFH ,!!.. if you are having an ASHP for DHW then there is no additional cost using it for UFH ( apart from the relatively low cost of the pipework and manifold. It’s been said on this forum that it’s wise to put the pipe in the screed when it’s built as it’s near impossible to do it afterwards. Plan for UFH but don’t buy the manifold and all your bases are covered.

[dpmiller]

speaking of passive circulators and cooling, is there merit to burying a loop under the slab to lose some heat to?

[hejdavies]

so what kind of temperatures are you getting in your PH in winter time. I've been to see a couple of PHs locally and my understanding is that it very rarely drops below 20 and, when it does, not by much. 

 

But perhaps it is just about "topping up"..

 

how much would you expect an UFH system to cost/m2?

 

[Guest Alphonsox]

11 hours ago, dpmiller said:

speaking of passive circulators and cooling, is there merit to burying a loop under the slab to lose some heat to?

 

In Northern Ireland !?! You're a real optimist My builder just laughed at me when I asked about cooling.

[Guest Alphonsox]

10 hours ago, hejdavies said:

so what kind of temperatures are you getting in your PH in winter time. I've been to see a couple of PHs locally and my understanding is that it very rarely drops below 20 and, when it does, not by much. 

 

But perhaps it is just about "topping up"..

 

how much would you expect an UFH system to cost/m2?

 

 

If you're happy to install it yourself it is a pretty cheap exercise in the big scheme of things. We installed ours with kit bought from Wundatrade. All very straight forward.

From memory our 100m2 install required around £200 worth of pipe plus £100 for the manifold and £150 for the pump set. I'm currently heating it with a 3kw immersion heater.

I would suggest installing the pipe and manifold as a minimum. It's a low cost investment if you don't end up using it then you wont have lost much.

 

Our place is built to passive spec but is in a very exposed location. We definitely require some level of heating to make the place comfortable. Passive houses require some form of heat input. Whether you can get that input just from the occupants and their activity (cooking etc) is going to depend on a number of factors. A good starting point would be to have a look at the heat loss spreadsheet at http://www.mayfly.eu/ (Do read the blog while you are there.). This should give you some idea of your heating requirement, you can then work out how you want to supply it.

[joe90]

Well, people that have visited my build ( yet to be finished but water tight) have said how warm it feels and we are yet to put any heating on. This morning with no heating on  it’s 18 degrees and warmer than the old parkhome I am renting that has heating!!!! 

[Gone West]

15 hours ago, jack said:

Also, don't let anyone tell you that you don't need heating in your bathrooms in a house with Passivhaus levels of insulation. We were convinced not to include it and it's one of the larger regrets I have about our build. We're now retrofitting IR panel heaters, but I'd have preferred UFH.

 

+1 You certainly need some form of heating in bathrooms in PH. We have electric towel rails in our bathrooms which keep those rooms warmer than the living areas and the towels nice and warm. The MVHR extract from those rooms recovering that heat.

[Gone West]

11 hours ago, hejdavies said:

so what kind of temperatures are you getting in your PH in winter time. I've been to see a couple of PHs locally and my understanding is that it very rarely drops below 20 and, when it does, not by much.

 

We had our Genvex and towel rails running through December, January and February for testing even though we weren't living in the house. The air temperature was set to 19C and the water temperature was set to 40C and the electricity bill was £43.20 for the three months.

[Nickfromwales]

16 hours ago, PeterStarck said:

It isn't necessary if the PH has a very low space heating requirement. We decided against needing wet UFH with the resultant saving in UFH heat source, pipework, manifolds, valves etc. If the space heating requirement is low enough it can be supplied by warm air through the ventilation system. We use a Genvex Combi 185 for our ventilation, warm air heating and DHW. The warm air heating and DHW is supplied by a 500W EASHP.

Did you have to fit larger bore ductwork or run the fan at a higher rate? Assume that is decided upon by the manufacturer / by design so possibly moot. 

[Nickfromwales]

17 hours ago, hejdavies said:

Hi all,

 

about to embark on self-build project. We have plot and planning. The layout optimises solar gain so I am keen to achieve passive house standard. 

 

I have noticed on this forum that many self-builders seem to include UFH in their passive house build but I have been told this is simply not necessary... So i'd be grateful for thoughts on this please!

Hi and welcome. 

Id be interested to hear, possibly from @PeterStarck, what the floor temp ( temp of actual floor covering that you walk on with bare feet ) sits at compared to the ambient temp as detected / denoted by the room thermostat  . I cant help thinking that if members such as @jack report wishing they'd installed UFH in the upstairs bathrooms because the floors weren't exactly comfortable underfoot, then the ground floor of even a Ph build would be 'worse' than that.

Can we filter out those with the "I'll wear slippers" PoV and get some real life feedback from any members WITHOUT ground floor heating please? 

[Gone West]

3 minutes ago, Nickfromwales said:

Did you have to fit larger bore ductwork or run the fan at a higher rate? Assume that is decided upon by the manufacturer / by design so possibly moot. 

No the ducting is 125mm diameter and is not a manifold system. I designed the ducting system myself and checked with Genvex that it was suitable. The Genvex Combi increases the fan speed automatically if it needs to supply warm air.

[Gone West]

@Nickfromwales I'll have a go later on. Mind you it depends on the insulating effect of the flooring material.

[Nickfromwales]

34 minutes ago, PeterStarck said:

@Nickfromwales I'll have a go later on. Mind you it depends on the insulating effect of the flooring material.

Agreed, and purely for research / information. I would appreciate it as one I'm looking at wants to heat via MVHR and a duct pre-heater. 

I will pay you suitably for the market research of course. Out of curiosity how much is one pint up your neck of the woods ? 

[joe90]

I confess to not bothering with duct heaters ( although an electric one is possible due to redundant cable being available) because of the doubt on this forum that the air volume in MVHR would be enough ( I have 68mm radial duct). Also it occurs to me that people have said they tend to run their MVHR at lower volumes than stated in the regs, so even less heat transfer?

[hejdavies]

1 hour ago, PeterStarck said:

+1 You certainly need some form of heating in bathrooms in PH. We have electric towel rails in our bathrooms which keep those rooms warmer than the living areas and the towels nice and warm. The MVHR extract from those rooms recovering that heat.

 

Thanks Peter... and is it fair to say that the electric towel rails suffice in the bathrooms - ie the floor is perfectly comfortable to walk on bare foot in the morning in winter..??

[Nickfromwales]

12 minutes ago, hejdavies said:

 

Thanks Peter... and is it fair to say that the electric towel rails suffice in the bathrooms - ie the floor is perfectly comfortable to walk on bare foot in the morning in winter..??

If it's tiles then get some, lay them on the floor overnight and then stand gently on them barefoot the following day when they're acclimatised. 

[joe90]

I used luxury vinyl tiles in our bathrooms because they are less cold to the touch ( in this country), I have electric towel radiators in both  and electric UFH in our ensuite .