Upstairs heating options for passivehaus - electric or wet systems; looking for advice

[Great_scot_selfbuild]

Looking for advice on electric UFH pads/loose wire laid to a plan. We don’t believe we’ll need it much if at all, but we’ve not met or spoken to anyone who has used it - effectiveness, cost, installation. Here’s our situation and some questions.

 

Our build will have a passivehaus level of thermal and airtightness. I’ve visited a similar size/build where they have wet UFH downstairs and only towel radiators in the bathroom upstairs; they have no issues with warmth upstairs.

 

(Numbers for ease of reference / comment)

 

Current thinking / starting point:

1. Wet UFH downstairs
2. Towel rails upstairs (electric)
3. Electric UFH pads in bathrooms (electric) 
4. The back-up: Install electric UFH pads in the bedrooms (not covering the whole floor area) as a reserve for cold snaps and the ability to apply some heat to the bedrooms that could be relatively effective (i.e. you’d be walking on it and so the impact of turning it on would have some relative immediacy of effect).

 

Alternatives we’re considering:

5. Install wet radiators (2 bathrooms) connected to the ASHP.

6. Would prefer not to install wet heating to the bedrooms (space, cost, don’t believe we’ll need it).

 

Question about electric UFH:

7. I’ve had slightly confusing explanation from a UFH supply company (clearly in sales, not technical). They described the electric pad installs (for both under tile and under carpet) as:

a) Tile backers required (are they essential).

b) Electric heating pad, or loose heating wire that can be laid to one of their designs, which allows it to fit around items (beds/baths) easier.

c) Self-levelling compound is mixed up to lay over the wire (as shallow as 10mm). We have a timber frame and timber first floor (Caberdek) and so I asked about this needing to be waterproofed - he didn’t have an answer.

 

I appreciate that’s quite a download, any comments/sanity checks appreciated.

[Bornagain]

Our self build is heading towards passiv haus, wall u value=0.15, roof=0.1, windows/doors=1.0, MVHR etc etc.

 

We heat the house with UFH downstairs into a very thick slab, we have no heating whatsoever upstairs.

 

if we built again, we would do the same, there is absolutely no need unless you want a very warm bathroom - we don’t.

 

[JohnMo]

With it being upstairs and if doors are open you are likely to have warmer bedrooms, like it not, I would keep it simple. Just install panel heaters in bedrooms or the provision for them, keep the electric UFH in bathrooms. But if you are going for a grant (I just wouldn't bother) they will require all heating by ASHP.

 

But to mess your head up more, are you likely to need cooling upstairs? If so just do fan coils for heating and cooling in bedrooms and bathrooms. Cool Energy do bathroom fan coil towel rails. Do mild cooling keep the water flow above dew point then no need for drains to be added.

[Great_scot_selfbuild]

4 minutes ago, Bornagain said:

Our self build is heading towards passiv haus, wall u value=0.15, roof=0.1, windows/doors=1.0, MVHR etc etc.

 

We heat the house with UFH downstairs into a very thick slab, we have no heating whatsoever upstairs.

 

if we built again, we would do the same, there is absolutely no need unless you want a very warm bathroom - we don’t.

 

Thank you!

[Great_scot_selfbuild]

3 minutes ago, JohnMo said:

But to mess your head up more, are you likely to need cooling upstairs? If so just do fan coils for heating and cooling in bedrooms and bathrooms. Cool Energy do bathroom fan coil towel rails. Do mild cooling keep the water flow above dew point then no need for drains to be added.

We did do a lot of thinking around this early on (pre-detailed SAP and modelled part O calcs). I think we’re good, but I’m going to look into this as what you’ve described is new to me - can you point to a couple of links of what you’re describing please?

[JohnMo]

https://coolenergyshop.com/collections/radiators-fan-coils?srsltid=AfmBOoo2Jwpa28-xTPSwQCmxyskK6onq3GBoEW004T_AV7JvfWtJQvZo

 

Here are a couple of photos of ours which heats a summer house (a Myson unit). First is the unit without the cover installed, controller is on the right, a finned radiator panel behind the sheet metal and a linear fan below it. It basically modulates the fan speed to maintain a a set room temp. Way smaller than an equivalent radiator.

 

[Thorfun]

We have wet ufh downstairs and electric towel rads and electric ufh in the bathrooms. 
 

our heating backup is our AC. Not needed it to heat yet at all. 
 

BUT…..we use the AC all the time in the summer. We have external blinds to keep the heat of the sun out but it’s nice to be able to look out of the windows so AC is essential. Plus as we use it in the summer it’s run off the solar so is effectively free to run. 
 

obviously, @JohnMo’s suggestion of fan coils would work but we decided to keep our systems separate which has advantages in my opinion. Plus a ducted AC system is extremely quiet and unobtrusive. Only thing I’d do differently if I was doing it again is install ducted AC everywhere rather than having wall units downstairs. 
 

Give serious consideration to keeping the house cool. 

[ProDave]

We have wet UFH downstairs and wet UFH upstairs only in the bathrooms.

 

We like a cool bedroom 17-18C is fine.  Most of the year to keep the bedroom that cool we need to keep the door shut.  In the cold weather we have been having for the last few weeks, we occasionally have to open the bedroom door to let a bit of heat up the stairwell in.

 

I fitted an electric point on the wall of each bedroom to fit an electric panel heater should it be required.  None have ever been needed.

[Bornagain]

43 minutes ago, Great_scot_selfbuild said:

Thank you!

As an afterthought, our stairwell is very open and this allows heat from downstairs to make its way into the upstairs rooms, we have to keep the bedroom doors closed  to keep them cool.

If your stairwell is very narrow then there is a possibility that the heat from downstairs won’t be able to make its way upstairs, it’s worth thinking about.

[FarmerN]

We are in a bungalow so not comparable.

 

I would recommend electric towel rails on a timer . Ours are on 3 hours a day, at cheap rate, hour and a half morning and night. Towels always dry.

Our towel rails have timer built in to element , but wish we had put the timer in the wiring circuit, probably back in plant room.

 

We have wet UFH which is on 9 months of the year but we have 90mm screed and tiles, with a different, warmer surface, might not need it. The floor and stone effect shower tray do dry quickly after a shower. Not had any heat on in bedrooms through the two winters we have been here.

We put a high level wire connection to take an infrared heater or similar if required but not needed it yet, but its there for when I am 90 if needed.

 

Both our neighbours in new builds, both with heat pumps and MVHR,  talk about over heating far more than heating, but both have a lot of glass. Overheating not been an issue for us but we have a lot less glass, and high level Velux windows we can leave open at night when warm.

[Nestor]

Recommend in bathrooms, electric UFH and electric towel radiators with accessible timers.

We have wet UFH elsewhere but not used in the first floor bedrooms since moving in. 

Cooling must be considered. I plumbed for independent AC (Not implemented yet).

As above keep it simple.

 

 

[SteamyTea]

Are you building in Surrey? (your username could suggest otherwise).

Regardless of what the climate change deniers say, you will have periods of 35° degree outside air temperatures, and the occasional sub -10°C winter temperatures.

Cooling, via UFH pipework will work well at the moment, but in two decades will probably struggle.

So fit the pipework now, use if necessary, and consider how you can fit AC later if it becomes necessary.

Your build will be around longer than all of us here, so, for what is probably a tiny cost, will pay dividends later.

[JohnMo]

37 minutes ago, SteamyTea said:

Cooling, via UFH pipework will work well at the moment

It does even with my 300mm pipe centres, its way more powerful when you get down to 100mm centres.

 

Uber simple to get working, set flat WC curve, say at 19 degs, let that run 24/7, to keep floor slightly cooler than rooms, have cooling thermostat to switch to second set point say 16-17 degs flow temp, when room temps hits 23 deg.

 

I will be using the smart grid terminals within the ASHP to demand a reaction of 2 Deg in flow temp. My UFH controller is switchable between cool and heat and so is the ASHP, so use a single repurposed light switch connected to both (used to provide a volt free open/closed signal), one position changes both to cool the other position to heat.

 

Pretty much a no brainer, very cheap to run, when between 10 and 25 outside the CoP is between 7 and 9 in the tick away mode, you still get a CoP over 4 running flat out in boost mode when its 35 outside.

[TerryE]

On 20/01/2026 at 07:50, Great_scot_selfbuild said:

Looking for advice on electric UFH pads/loose wire laid to a plan. We don’t believe we’ll need it much if at all, but we’ve not met or spoken to anyone who has used it - effectiveness, cost, installation

 

None?  We have 3 story passiveClass house in NN7.  Lived in it for 8 years now.  We have no heating on the top two floors. The master bedroom en-suite has a 60W towel rail on a Zigbee-enabled fused spur which automatically turns on overnight for about 6 hours in the heating months. We have an electric oil-filled rad in the hall well that outputs about 1kW and the CH system turns on as necessary in the cheapest (typically)  4-6 hrs on the Agile tariff in the winter months. This tops up the upper floors.  Our master bedroom is about the coldest in the house and its at ~ 20°C ATM.

 

It the house as constructed is truly energy efficient then you won't get a 10-15 payback on the installation costs of fancy solutions that you'll never use.  E.g. that hall rad costs us maybe £100 p.a. and does the job.  Do the math. 

[Adrian Walker]

The reason that some people put heaters in bathrooms is that after a shower, you are wet & naked and Evaporative Cooling takes place. If this is a problem, it's better to use infrared heaters/panels. You certainly don't need any UFH, either wet and electric upstairs in a Passive House.

[Great_scot_selfbuild]

19 hours ago, SteamyTea said:

Are you building in Surrey? (your username could suggest otherwise)

Yes; we have lots of Scots Pines on the plot. Coming up with a name wasn't something I spent much time thinking about 🤣.

19 hours ago, SteamyTea said:

So fit the pipework now, use if necessary, and consider how you can fit AC later if it becomes necessary.

Indeed!

[Thorfun]

9 hours ago, Adrian Walker said:

You certainly don't need any UFH, either wet and electric upstairs in a Passive House.

But I like a nicer warmed tiled floor. Feels good underfoot. So it may not be “needed” but it’s certainly wanted!

[torre]

32 minutes ago, Thorfun said:

it may not be “needed” but it’s certainly wanted!

A good point that we sometimes lose track of. Heat loss calcs etc are great for working out the 'need', but the 'want' is just as important, so for us (wet) upstairs ufh is both about avoiding cold floors and avoiding any rad/fan coil fixtures on the walls

[JohnMo]

30 minutes ago, torre said:

upstairs ufh is both about avoiding cold floors

I must be doing something wrong, I have to wait until temps drop to about -5 before I feel warm floors. Until then they aren't cold but certainly aren't warm.

[ProDave]

If doing a lot of work yourself, then things can be very cheap.  e.g. My wet UFH for the 2 bathrooms, the pipe and spreader plates were leftovers from doing the downstairs, so all I had to buy to put wet UFH in the bathrooms was a small manifold a 2 port motorised valve and a few plumbing fittings.

[Thorfun]

10 minutes ago, JohnMo said:

I must be doing something wrong, I have to wait until temps drop to about -5 before I feel warm floors. Until then they aren't cold but certainly aren't warm.

i have the electric ufh in the bathroom set to 28°C in the morning and evening (the main times we use the bathroom) and can definitely feel the warmth! it's so nice to step on to.

[saveasteading]

12 hours ago, TerryE said:

Do the math. 

Maybe this is in jest. But we should use British English on this site to maintain our good  example and credibility.

[Nestor]

Does depend a bit on the floor covering.

Tiled wet room and the UFH is in use over the winter, the other bathrooms with cork flooring have never required heating.

 

[JohnMo]

2 hours ago, saveasteading said:

But we should use British English

Yep

But not BTU's or inches for that matter.

[saveasteading]

Oops. I still order 6 x 2.

But I make sure a joist hanger is 47mm.

My excuse is that a 6 x 2 is not a measurement but the name of a component.

 

And I measure in yards if pacing in slippy conditions.