Debating removing the 1st floor UFH in a Passivhaus

[puntloos]

House build progressing nicely, now thinking about flooring. We currently have designed UFH on both floors, but on the 1st floor we have mostly carpet, tog is a problem. (currently arriving at 2.3 total incl underlay). As a reminder, we also have fan coil units in the primary bedrooms that can heat. 

 

My question: does it make sense to just save some money and remove UFH from the first floor? When things are cold I can certainly heat the room surgically with my R32 Fan Coil Unit (the target heat load in my bedroom is 300W, two bodies generate 160.. I need 140 more..) , but my architect is concerned that a 'cold' first floor, requires the ground floor to 'overheat', hoping that the MVHR will slowly move heat around. Effectively a stratification issue, and just heating the first floor when needed (even with high-ish tog) would be a more reliable approach.

 

Thoughts?

 

 

[mike2016]

There's not going to be THAT much temp difference between the floors surely? I like a cooler bedroom. Do you have an office or someone who likes it warmer to cater for? All the rooms are within the fabric and with PassivHaus the temp swing would be minimal without solar gain skewing things. Leave upstairs doors open a bit to spread the heat. Fan coils should work fine to top up. Ufh upstairs I would drop. 

My plan is for NO ufh at all, air to air with two internal cassettes, one in living/dining/kitchen open plan downstairs and a second in upstairs office and that second one is optional according to my heating consultant. He said ufh is overkill for me. Separate monobloc a2w for hot water that vents directly to outside. I have a very small house though, 102m2. This approach halves my heating system install costs too.

Edited June 29, 2023 by mike2016

[Mr Punter]

If you have a towel radiator in each bathroom it will give plenty of heat for the bedrooms.  The UFH on the first floor is money wasted.

[Iceverge]

No need for any central heating in passivhaus. We get by on a single plug in rad downstairs. 

 

The only good reason I can think of for UFH upstairs is cooling. 

[Dan F]

Just now, Iceverge said:

The only good reason I can think of for UFH upstairs is cooling. 

Fancoils are going to a better approach for cooling than UFH though, especially on the first-floor and given carpets.

[ProDave]

I am one of several here that "took the leap of faith" and did not install upstairs heating.  *

 

Like those before me that said you would not need upstairs heating, I can confirm they were right, and we do not need heating upstairs  Yes in the winter it can be a couple of egrees cooler than downstairs but that is how we like it.

 

* i did install electric points should we need to add an electric panel heater in each bedroom that have remained unused.  And there is IFH in the en-suite and bathroom running at a low temperature more to ensure the tiles don't feel cold.

[puntloos]

My team brought up a few points:

 

1/ Additional cost for one more UFH floor is only about 4000GBP extra.. ok nothing to sneeze at but to retrofit it after the fact is a huge pain.

2/ With no UFH on 1st, the downstairs UFH will have to heat more, in particular also the concrete floor (the ceiling of ground floor) 

3/ thick(ish) carpet will not really stop heat, it will just slow it

4/ For small houses, it's easier to maintain a good 'de-stratification' (horizontal and vertical) but my house is 250sqm, arguably on the larger side, so indeed it'll take longer for a MVHR to move stuff around.

5/ I have one completely unheated room which might be a bit of a problem if it's cold out

 

End of the day. I think my #1 point is the thing that's swaying me, futureproofing and just a more homogeneous air distribution.

[Jenki]

4K for 125SqM UFH 😯. 🛣️👨.

[Iceverge]

You could probably bank more of the heat in a time of use tarrif considering it's a concrete first floor. 

 

That and run the ASHP at a lower flow temp due to the larger emitter area thus boosting your COP. 

 

I don't think you need it. A few UFH mats under the tiles would suffice but if you do choose to do it, it's not all negative. 

[joth]

33 minutes ago, puntloos said:

2/ With no UFH on 1st, the downstairs UFH will have to heat more, in particular also the concrete floor (the ceiling of ground floor) 

 

This is only if you're heating the house up from freezing to target temperature. In a PH this rarely (virtually never) happens.

Once at target temperature, the ASHP is not "Heating" the concrete of the FF, or any of the fabric that is already within the thermal envelope. That's already at temperature. The ONLY job of the heating system (ASHP+UFH) is to replace heat energy that is lost out through the thermal envelope. In this respect, the concrete first floor is as much your friend as your enemy, as it is a big fat thermal store (so-called thermal mass) that slows down the rate of loss as proportion of energy in building when e.g. doors or windows are opened briefly. [analogy: if your bucket has a hole yay big in it, leaking 1L/min, you need to top up the bucket at 1L/min to maintain its level. The volume of the bucket is entirely irrelevant, unless you're silly enough to let the bucket empty and then need to heat it from nothing]

Yes, without the FF, the GF UFH will have to do all this work. Except it won't, as you already mentioned here and elsewhere you have several kW electrical appliances doing most the work (hint: relocate some of them upstairs /hint), and then there's those FCUs available to help too.

 

Anyway point #1 is unassailable, and it's in essence the reason I'd always suggest putting UFH in the GF even if PHPP says it's not needed, so if that's the decider on its own, the rest of this conversation is entirely academic 🙂

[puntloos]

16 minutes ago, joth said:

This is only if you're heating the house up from freezing to target temperature. In a PH this rarely (virtually never) happens.

Once at target temperature, the ASHP is not "Heating" the concrete of the FF, or any of the fabric that is already within the thermal envelope. That's already at temperature. The ONLY job of the heating system (ASHP+UFH) is to replace heat energy that is lost out through the thermal envelope. In this respect, the concrete first floor is as much your friend as your enemy, as it is a big fat thermal store (so-called thermal mass) that slows down the rate of loss as proportion of energy in building when e.g. doors or windows are opened briefly. [analogy: if your bucket has a hole yay big in it, leaking 1L/min, you need to top up the bucket at 1L/min to maintain its level. The volume of the bucket is entirely irrelevant, unless you're silly enough to let the bucket empty and then need to heat it from nothing]

I'm not sure I fully follow - the mental model I have in my head is that if we assume the first floor is colder than expected, that means heat will drain out of the (presumably at target) concrete floor into that room. This means that immediately, the concrete is also ever so slightly below target. 

 

I imagine that you're right there will be an average "target temp" in the house, so this is not necessarily an issue of adding heat to the house but redistributing it properly, and with no heat source on first, the concrete will be somewhat of a heat sink for the ground floor, no?

16 minutes ago, joth said:

Yes, without the FF, the GF UFH will have to do all this work. Except it won't, as you already mentioned here and elsewhere you have several kW electrical appliances doing most the work (hint: relocate some of them upstairs /hint), and then there's those FCUs available to help too.

This is true, and our plan is to pull heat from the devices into the MVHR as much as possible, and FCU as backup. But I agree no direct "device-to-1stfloor" link exists.. 

16 minutes ago, joth said:

Anyway point #1 is unassailable, and it's in essence the reason I'd always suggest putting UFH in the GF even if PHPP says it's not needed, so if that's the decider on its own, the rest of this conversation is entirely academic 🙂

 

Then again I like academies

 

But yeah, as many people here found out, whether or not specific rooms in your house are either too hot or too cold is sometimes harder to predict than it seems, and for a decent amount of change I can be (more) sure that it will not trip me up and run up huge costs later.. but.. also don't want to be truly wasting my energy if it's never going to be a problem..

[joth]

7 minutes ago, puntloos said:

I'm not sure I fully follow - the mental model I have in my head is that if we assume the first floor is colder than expected, that means heat will drain out of the (presumably at target) concrete floor into that room. This means that immediately, the c

change the mental model from "FF is colder than expected" to "FF is leaking heat energy faster than expected".

Now, if it is leaking fast, how is it leaking? Probably via windows, conducting or convecting (drafts) or perhaps through the walls. Any of these mean the air will start to cool down *long* before the concrete floor starts to appreciable cool. After all, the high tog carpets are keeping that concrete nice and cosy warm as discussed as where. So somehow we need to get more energy into the air to replace the loss. This could come through MVHR (unlikely to shift enough energy to make a difference), natural convection (very possible if doors are left open), directly heating the air (FCU, humans  or electrical appliances in the room) or if they're not enough it will come from material of the building, first walls and ceilings (unless they have high tog wallpaper on them) and last of all from the floor (as that's insulated with carpet).

Anyway tldr you could have zero concrete on the FF or a million tonnes, but if the whole house heat loss is 5kW, all going out through the roof, the GF UFH needs to supply a steady 5kW regardless of the quantity of concrete in there. It'll just be a steeper energy gradient (i.e. colder upstairs than down).

 

[Thorfun]

1 hour ago, Jenki said:

4K for 125SqM UFH 😯. 🛣️👨.

+1. is it gold plated pipes I wonder? 

[JohnMo]

Must say, my UFH and heat pump cost about the same or less than that.

[SteamyTea]

17 hours ago, puntloos said:

architect is concerned that a 'cold' first floor, requires the ground floor to 'overheat', hoping that the MVHR will slowly move heat around. Effectively a stratification issue

Yes, a stratification issue.

I get about a 3 K temperature difference between floor and ceiling during the heating season.

There are a number if areas to calculate. Assume that the top layer of air downstairs is 1 K higher than the mean downstairs temperature. Then assume your upstairs floor is 4 K cooler than the ambient downstairs. Work out the power going though the floor. 

May find that with a delta of 5 K, your numbers i.e. 140 W are not far out.

You can also increase the MVHR pipe diameter, this should help increase power delivery to the upstairs, and reduce noise. Easy to do if MVHR is in loft.

Then think about your lifestyle. How many non sleeping hours do you spend upstairs? Not many I suspect. 

As usual, it comes down to the numbers.

[SteamyTea]

On 29/06/2023 at 18:54, puntloos said:

I'm not sure I fully follow - the mental model I have in my head is that if we assume the first floor is colder than expected, that means heat will drain out of the (presumably at target) concrete floor into that room. This means that immediately, the concrete is also ever so slightly below target

Heat loss is not purely from heated slab to room air. The rest of the room is also losing heat.

Just do some power calculation, they are not dependant, in themselves, on temperature. That is the second part of the simultaneous equation (remember them from skool).

[ProDave]

The ability of a well insulated air tight building to distribute it's heat quite evenly throughout the building is quite remarkable.

 

The one that astounds me it my workshop (aka plant room) which is the room above the attached garage.  There is no heating in there, the floor is the garage ceiling, it has the end gable wall, and it's "ceiling" is the garage roof.  There is no obvious way heat can get in from the rest of the house, the door between this workshop and our bedroom is usually shut.

 

I did have a spare mvhr extract port so have an mvhr extract in the workshop so it will slowly draw in air from the bedroom, that is about the only plausible source of heat input I can imagine to that room.

 

Yet still it is never particularly cold in there, and never needs any heating.

 

Just delete the upstairs heating and carry on building. 

[SteamyTea]

There is one note of caution, if you come to sell the house, new viewers may distrust the 'no heating upstairs as it is not needed' position.

 

A slightly bonkers idea would be to run the upstairs heating loop on a small secondary heat pump and use that harvested energy to control the upstairs air temperature, and dump the excess energy into your DHW.

Edited June 30, 2023 by SteamyTea

[Kelvin]

I followed the experience of others on here and didn’t put any heating upstairs. I’ll wire for wall heaters just in case but based on the last few months building the house it’ll be fine. Definitely no need in a truly passive house. 

[puntloos]

Interesting stuff.

 

The key issue is that there's quite a few stories in this forum with 'hard to fix' issues should something unexpected happen. 
 

Trying the safe side with things, so e.g. putting in unused stuff (eg UFH loops but not connect them) is an idea, but in many cases I found that once the 'hard' part is done the easy part is too easy not to do outright anyway.  And yea @SteamyTea pipe diameter point, downstairs I have very few options to enlarge.. upstairs, well, if I want to sacrifice ceiling or wall space... hmm.

 

So yes, about a GBP 3000 saving with extra peace of mind, of buy myself a nice family holiday.. hmm

[JohnMo]

We have bedroom UFH, if I was doing it again I wouldn't bother. I would instead do something that responds quickly if needed, such as an electric panel heater. Add the wires as @ProDave has done, then move on. Space and electric allocated should you feel the need at a later date.

 

Your UFH is then just downstairs and in bathrooms. Operate as a single zone, no mixer or pump on manifold, no wiring centre and a single thermostat or heat pump controller if thermostat built in. No buffer needed either.

 

Add an electric towel rail in bathrooms to dry towels and top up heat if required.

 

Simple - as a passivhaus should be.

[Dan F]

3 hours ago, puntloos said:

So yes, about a GBP 3000 saving with extra peace of mind, of buy myself a nice family holiday.. hmm

 

Putting in a backup on the first floor in case you find you don't like FF a couple of degrees colder than GF is a good idea.  Some people allow for future radiators, but UFH is probably a better solution (albeit more expensive) given it's hidden.

 

That said, given you have fan coils in first floor rooms, you already have a solution for taking off the chill on the first floor, and therefore I'd argue that you don't need both UFH and fan coils.  So I'd personally definitely save the money and not install the UFH in this case.

Edited June 30, 2023 by Dan F

[Dave Jones]

if your air tight wont need it.

 

Surprised your passiv designer even specified it which is worrying.