UFH versus Radiators

[Robert Clark]

In a timber frame Passivhaus which would you choose, UFH or radiators?

 

[Russell griffiths]

I don’t even think radiators are worth a second thought. 

Just from the point of view that they take up wall space, I wouldn’t ever consider them. 

[ragg987]

From a comfort perspective, UFH every time as it removes localised hot-spots and cold-spots. Are you using a ASHP? These are more efficient at low temperatures, and rads will need warmer water.

[Jeremy Harris]

14 minutes ago, Robert Clark said:

In a timber frame Passivhaus which would you choose, UFH or radiators?

 

 

Probably UFH, but bear in mind that UFH will always be less efficient than radiators, although for a house with a low heating requirement these losses won't cost a lot.  As an example, we have 300mm of EPS under our passive slab, and the UFH heat loss to the ground beneath is ~8% at the maximum heating level.

[ragg987]

Another option is warmed air through the MVHR - only possible if your energy requirements are very low, else you have to heat the air a lot and this is unpleasant for the occupants.

 

I use UFH at ground and basement, and heated air through MVHR in bedrooms.

[jonM]

I was given a very strong recommendation by an experienced Passivhaus M&E designer and architect to use radiators on the basis it is cost effective, quicker to respond than burying pipes in a slab and easier to maintain. You can still circulate water at lower temperatures  for efficiency purposes but will need to oversize your radiators. 

 

The thought of underfloor heating is tempting and more aesthetically pleasing but I don't think it is an open and shut decision particularly in a passivhaus. 

 

You can also put the radiators anywhere in the room in a passivhaus. They don't need to go under a window as in a conventional house. 

Edited April 27, 2019 by jonM

[Robert Clark]

38 minutes ago, ragg987 said:

From a comfort perspective, UFH every time as it removes localised hot-spots and cold-spots. Are you using a ASHP? These are more efficient at low temperatures, and rads will need warmer water.

 

Not sure about the heat source yet. It’s certainly going to be electric as we’ve no gas so either ASHP or maybe a Willis Immersion.

Was initially looking at a Sunamp, but am not convinced that they have sorted out their controls issues yet

[Robert Clark]

39 minutes ago, JSHarris said:

 

Probably UFH, but bear in mind that UFH will always be less efficient than radiators, although for a house with a low heating requirement these losses won't cost a lot.  As an example, we have 300mm of EPS under our passive slab, and the UFH heat loss to the ground beneath is ~8% at the maximum heating level.

 

What would you suggest for the first floor?

[Robert Clark]

6 minutes ago, jonM said:

I was given a very strong recommendation by an experienced Passivhaus M&E designer and architect to use radiators on the basis it is cost effective, quicker to respond than burying pipes in a slab and easier to maintain. You can still circulate water at lower temperatures  for efficiency purposes but will need to oversize your radiators. 

 

The thought of underfloor heating is tempting and more aesthetically pleasing but I don't think it is an open and shut decision particularly in a passivhaus. 

 

You can also put the radiators anywhere in the room in a passivhaus. They don't need to go under a window as in a conventional house. 

 

Our architect is also recommending radiators, however it looks like UFH is popular with owners of low energy houses 

[Jeremy Harris]

11 minutes ago, Robert Clark said:

 

What would you suggest for the first floor?

 

I wouldn't bother with first floor heating at all, as I doubt you'll need it; enough heat will rise from below.  We don't have any heating on the first floor, bar low power heated towel rails in the bathrooms, that only come on for an hour or so morning and evening.  The bedrooms are plenty warm enough, although I did fit fused connection units in both so we could add small electric panel heaters if needed (they won't ever be needed, as it happens).  The only thing I'd do differently would be to fit low power electric mats under the tiles in the bathrooms, to just take the chill off when standing on them in bare feet.  The bathroom floors aren't cold (typically ~21°C) but a few degrees warmer would feel nicer when in bare feet.  If doing this, then the only thing to watch would be to keep the power right down, as our bathrooms get quite warm as it is, so any floor heating would have to be limited to only times that the bathrooms are in use.

[Robert Clark]

1 minute ago, JSHarris said:

 

I wouldn't bother with first floor heating at all, as I doubt you'll need it; enough heat will rise from below.  We don't have any heating on the first floor, bar low power heated towel rails in the bathrooms, that only come on for an hour or so morning and evening.  The bedrooms are plenty warm enough, although I did fit fused connection units in both so we could add small electric panel heaters if needed (they won't ever be needed, as it happens).  The only thing I'd do differently would be to fit low power electric mats under the tiles in the bathrooms, to just take the chill off when standing on them in bare feet.  The bathroom floors aren't cold (typically ~21°C) but a few degrees warmer would feel nicer when in bare feet.  If doing this, then the only thing to watch would be to keep the power right down, as out bathrooms get quite warm as it is, so any floor heating would have to be limited to only times that the bathrooms are in use.

 

Assuming I was using an ASHP for the ground floor UFH, would you suggest using this for the towel rails too?

Like the idea for the electric underfloor mat in the bathrooms

[jonM]

5 minutes ago, JSHarris said:

I wouldn't bother with first floor heating at all,

 

Worth taking into account what temperature you like your bedrooms at, whether you have any living areas upstairs, whether you have cathedral ceilings etc. 

[ragg987]

3 minutes ago, JSHarris said:

I wouldn't bother with first floor heating at all, as I doubt you'll need it; enough heat will rise from below

My experience is different. On our PH-standard build, and despite no insulation between ground floor and first floor we do not get sufficient heat from below to keep bedrooms warm enough. I was getting conflicting feedback from other people in this situation so decided to fit direct electrical heater in upstairs MVHR ducts as a precaution. Plus low-energy towel rails in bathrooms.

 

I'm glad I did this as we do need it. In winter I keep towel rails on 24x7 (perhaps about 50W on average - guesstimate). I also have a thermostat and timer for upstairs MVHR heating, it is usually enough to switch on for 1 to 2 hrs each morning and early evening to take the chill off in the rooms, without over-heating for sleep.

[Jeremy Harris]

5 minutes ago, Robert Clark said:

 

Assuming I was using an ASHP for the ground floor UFH, would you suggest using this for the towel rails too?

Like the idea for the electric underfloor mat in the bathrooms

 

Given the cost of running pipework and controls for the towel rails, compared to the cost of just sticking a low power element in a towel rail, I'd say it's probably not worth the hassle.  Our towel rails are both fitted with 70 W heating elements, and are on a time switched circuit, so they come on for a total of two hours per day.  With both on they cost less than 5p a day to run.  We usually only have one of them on, so the cost is less than half that.

[ProDave]

The "no upstairs heating" thing does seem a bit variable.

 

Like others I have no specific heating in the bedrooms. I have UFH in the bathrooms mainly so the tiles are comfortable to walk on.

 

Most of the time the bedrooms are warm enough, but in a really cold spell they occasionally get a bit cool, so then I light the stove and heat the downstairs to "indulgance" level (about 25 degrees) and let the heat from that work it's way upstairs.

 

I do have electric points for panel heaters but I don't expect to ever be using them.

 

[Jeremy Harris]

5 minutes ago, jonM said:

 

Worth taking into account what temperature you like your bedrooms at, whether you have any living areas upstairs, whether you have cathedral ceilings etc. 

 

2 minutes ago, ragg987 said:

My experience is different. On our PH-standard build, and despite no insulation between ground floor and first floor we do not get sufficient heat from below to keep bedrooms warm enough. I was getting conflicting feedback from other people in this situation so decided to fit direct electrical heater in upstairs MVHR ducts as a precaution. Plus low-energy towel rails in bathrooms.

 

I'm glad I did this as we do need it. In winter I keep towel rails on 24x7 (perhaps about 50W on average - guesstimate). I also have a thermostat and timer for upstairs MVHR heating, it is usually enough to switch on for 1 to 2 hrs each morning and early evening to take the chill off in the rooms, without over-heating for sleep.

 

Good points, as I think one reason we get good heat transfer from the ground to first floor may well be because we have a central hall that extends right up to the internal ridge of the house, so a fair bit of heat rises up that.

 

I have noticed that the temperature on the landing will often be a bit too warm (not uncommon for it to be around 24°C at times), so we keep the bedroom doors closed so they don't get too warm.  We don't like the bedrooms to be over about 22°C, and prefer them to be cooler than this if possible.

[nod]

UFH every tine. Very little difference in running costs 

When you have a lot of glass and low windows Combined with open-plan Its difficult to find somewhere to site all the radiators 

Also should you sell on at a later date It’s a massive selling point

[ragg987]

A couple of other factors (for me) in my decisions for UFH:

• with an ASHP I can put the HP into reverse and add cooling into the house. Cool-floor. I doubt you can do this with radiators, if the water is below about 15C you risk condensation. Have used this in the very hot summer (2018) and it does help, though not as good as direct air-cooling would be.
• Passive heat distribution - by running water through the UFH I thought I could re-distribute heat e.g. sun shining through the windows heat the floor and the energy is shifted to the north side of the house or to my basement. Not sure if this actually works in practice.

In theory @jonM 's architect is right. With a PH your heat requirement is between 1 and 3kW for a small to medium size house, so the complexity and expense of UFH is not needed. In theory you can get away with a single fan heater. But you are comparing point to distributed heat sources and this is where comfort (human perception) comes into play.

 

I once came across some research about how humans perceive warmth and hence comfort. Unfortunately I did not clip it and have been unable to find it again. The research was in the context of flooring materials. It concluded that, when people walk on a floor that feels cold (e.g. hard tile) they feel cold even if the air temperature is fine. But if the floor feels warm (e.g. carpet) then they feel warm even if the room is a bit cooler. I believe UFH goes some way to providing the "all-round" warmth / comfort perception.

 

One thing to note in UFH vs rads is that rads are great when you come in after a walking the dog in the cold and need to warm your body up - you can lean against the warm surface and this is a lovely feeling. You don't get this with UFH.

[Ferdinand]

Personally I would lie down on the ufh. ?

[Ed Davies]

3 hours ago, ragg987 said:

Are you using a ASHP? These are more efficient at low temperatures, and rads will need warmer water.

 

Indeed you can run UFH at lower temperatures than radiators but I'm not entirely convinced that it makes that much difference in a well-insulated house if you run the radiators for long periods of time.

 

E.g., in the leaky Edwardian house I'm renting at the moment the average temperature of the flow to the radiator in the study over December 2018 and January and February 2019 was 30.46 °C to kept the room around 22 °C most of the time it was occupied. (Maximum was 54.75 °C).

 

Here's a particularly cold period from January 17th to 24th when I left the heating on overnight for the first few days (Thur, Fri, Sat, Sun). There are only a few short periods, when the house is heating from cold, where the radiator runs continuously; the rest of the time the heating is cycling on and off. For the days when the heating was on continuously (Fri 18th to Sun 20th inclusive) the average radiator temperature was only 29.17 °C.

 

Radiator output is not quite linear with temperature so the output if it's just held at the average value will be a bit lower than if it's cycling up and down but I don't think this makes a huge difference, certainly not a much at the T⁴ effect that some people obsess on.

[Ed Davies]

3 hours ago, JSHarris said:

The only thing I'd do differently would be to fit low power electric mats under the tiles in the bathrooms, to just take the chill off when standing on them in bare feet.  The bathroom floors aren't cold (typically ~21°C) but a few degrees warmer would feel nicer when in bare feet. 

 

Or use a less conductive material? I'm quite partial to cork tiles for bathrooms and even bedrooms.

[Gone West]

I have a TF PH and I use electric towel rails in the bathrooms, supplemented with warm air heating from an EASHP through the ventilation system, to heat the house. If my house was at the higher end of PH heating requirement I would rather use skirting radiators than UFH.

[Jeremy Harris]

3 hours ago, Ed Davies said:

 

Or use a less conductive material? I'm quite partial to cork tiles for bathrooms and even bedrooms.

 

If it had been down to me, then I'd have laid cork flooring.  I laid it in the bathrooms of two houses I lived in before I met my current wife and it was very nice underfoot.  Unfortunately, SWMBO was set on having travertine on the bathroom floors...

 

2 hours ago, PeterStarck said:

I have a TF PH and I use electric towel rails in the bathrooms, supplemented with warm air heating from an EASHP through the ventilation system, to heat the house. If my house was at the higher end of PH heating requirement I would rather use skirting radiators than UFH.

 

I tend to agree with you about using skirting radiators.  They do seem to work well (a friend has them) and they offer the best of both worlds, being as unobtrusive as UFH and as efficient and responsive as radiators. 

 

I suspect that they might work with a cooling system, too.  We've certainly found that using the UFH in cooling mode works pretty well, as does just running the circulating pump to even heat out around the house, but this might well work just as well with conventional radiators or skirting radiators, as long as the temperature isn't dropped too low.  I run our floor cooling with a flow temperature of 12°C, which never seems to drop the floor surface below about 18°C, and that isn't low enough to cause any condensation problems.

[Stones]

7 hours ago, ragg987 said:

From a comfort perspective, UFH every time as it removes localised hot-spots and cold-spots. 

 

+1 - nice even temperature and you would have the ability to cool the house if fitting as ASHP

 

7 hours ago, ragg987 said:

 Are you using a ASHP? These are more efficient at low temperatures, and rads will need warmer water.

 

We had a low temp radiator based system in our last house (fed off a heat pump) - worked perfectly well, but pipework and radiators need to be sized for low flow temps (3 to 4 times bigger than an oil/gas radiator system)

[Onoff]

Mike Harding did a good sketch on buying a house and every room was done in cork...