Underfloor Heating downstairs, Aluminium Radiators upstairs

CHorn

In a new build we went for underfloor heating with 6 zones (1/room or area), then chose Aluminium radiators for upstairs (4 of them). The UFH downstairs works great.

Upstairs is a different story. The water going into them is hot, but nowhere near as hot as the water I'm used to going into a regular (steel?) rad, which would have been too hot to hold the entry pipe for long or at all. The water going into the new Aluminium rads at the entry pipe is hot but you can keep your hand there permanently no problem. Worse on recent cold days approaching or at 0c outside, with the temperature set to 21.5 the rads can barely get to 19 going flat out 24/7.

We're being told this is a 'slow heat system', and that if we turn the heat up on the UFH downstairs it will compensate, which it of course will. But then why have the upstairs rads at all? Or what's the point of paying for a heat system in one (upstairs) area of a house when the only way it works is if you compensate for its poor performance by turning up the heat in another (faraway, downstairs) part of the house?

My own thought is these are 2 separate systems designed to work independently, not in tandem so one compensates for the shortcomings of another. And that if you don't put sufficient energy in in terms of adequately hot water, the aluminium rad won't radiate enough heat as is happening here.

Or is there something special about these systems I don't get? Along the lines of the 'slow heat system'- every time the builder re-explains it to me and I say I don't get it he looks at me as though I'm some poor dumb sod. The only thing special it seems about aluminium rads other than cost is they heat faster (and cool faster) but if a system is working flat out 24/7 to reach a temp it never gets too, there's something wrong with the (hot water) energy being piped in.

The simple solution I've suggested is increase the heat of the water being piped into the rads, but for some reason that's not an option for the builder- or too costly or too complex or some other reason. Please help me in my ignorance, thanks.

John.G

What is the heat source, is it a boiler or a Heat Pump??.

Wearb

Aluminium radiators allow the radiator to be smaller than an equivalent output steel one.

Probably not worth the difference if space and appearance isn't a problem.

CHorn

https://www.boards.ie/discussion/comment/121475242#Comment_121475242

Heat Pump.

CHorn

https://www.boards.ie/discussion/comment/121475308#Comment_121475308

Thanks. Yes I know, which is why we went for alu over steel, but that's not the issue here.

John.G

What is the HP flow temperature?, generally, rads will/should be oversized by a factor of X2 to allow for the lower flow temp from the HP of 40/45C required to enable a decent COP.

CHorn

https://www.boards.ie/discussion/comment/121475603#Comment_121475603

Don't know, which is another reason for alarm. I've asked for a manual to operate the (Joule) system, and no manual or instrux in sight yet 6 months in and with winter now here. When we moved in in April I pointed out the heat going into the alu rads was only hot to the touch but not very hot as in you can't keep your hand on it, but was dismissed with the 'slow heat system' remark. Back then it was too hot outside to test any heating system, so I just said we'll have to wait for winter so and filed it away.

Now winter IS here and testing shows with the rads full on 24/7 we're only getting to 19 with thermostat set to get it to 20.5, which is of course what I suspected would happen. But is it normal for a heat pump system to distribute much lower temp water? Or is there a way- which is my suggested solution- to just give the rads the heat they want/need and we're then all sorted? Why this is such an issue/problem for the builder and he keeps ducking and diving I just don't know- seems a very simple solution to me- but it has me worried.

It seems to defy logic to tell me to heat other rooms downstairs to get the upstairs hotter- it will of course work, but what's the point in heating rooms you're not using at all to get heat (very inefficiently) into another elsewhere? Or even buying rads for upstairs when you're now relying on downstairs UFH to heat upstairs?

Just for context, it's an upside down house so living areas are upstairs, bedrooms downstairs, and a number of bedrooms not used or they don't need (much) heat during the day.

John.G

You can't just wind a HP flow temp up/down like a gas/oil boiler, you can get high(er) temperature models, maybe up to 55/60C but would cost a fortune to run, hence the oversizing of the rads to enable low temp running which shouldnt though mean "a slow heat system". Can you also compare the rad(s) inlet/outlet temperature feel, generally with low temp systems the circulation flowrate is high to increase the output so there may only be ~ 5C difference.

Can you post a screen shot of the HP make/model etc, should be able to download a manual from that, the flow/return temps should/might be displayed somewhere in a menu, will have a look.

Also the UFH manifold(s) usually have flow and return thermometers so taks another shot of these, if accessible, this will give a idea of the HP temperatures.

How is the domestic hot water heated??.

Wearb

You say the rads barely getting to 19 °C. Are you saying that this is what the room stat is telling you the room is reaching.

If eg you turned the stat to 25 °C, would the room temperature go above 19 °C ?

Sleeper12

Rads on a heat pump are only supposed to be Luke warm. If these rads were hot you would be only getting a cop of 1 or 2 and it would be a very expensive system to run.

I would suggest that the rads are undersized if they aren't heating the upstairs sufficiently. Increasing the output temperature isn't a solution as you will need a 2nd mortgage to pay the electricity bill.

The real test would have been the cold snap last week. In your opening post you complain about the heat of the rad but I don't see mention of the heat of the rooms themselves. Were they too cold during cold snap?

CHorn

https://www.boards.ie/discussion/comment/121475863#Comment_121475863

It's a Samsung AE120RXYDEG Heat Pump: https://imgur.com/IpAmIeG (I did look for manual but only got marketing material and some data specs which were meaningless to me). There's very little difference between in/out pipe temps, as you say <5C. On manifolds, pretty inaccessible but I'll take a look tomorrow when there's more light. Thanks.

CHorn

https://www.boards.ie/discussion/comment/121476063#Comment_121476063

19C is what room stat is saying it currently is, independently verified by another stat. I'm trying to get to 20.5C and that's what I've set stat for (and all stats are working fine, it's just the hot water temp in rads that's the problem).

But whatever I reach for, if it's cold outside as this week it only gets to c19. If it was even colder outside it would probably struggle even harder, so if it was -XC, it might get to 17 or 18, but wouldn't know for sure as that level hasn't been tested this winter- yet.

ongarite

20.5 for a bedroom is very warm. The 19 you can reach is the ideal & most efficient.

Your posts contradict themselves. You say downstairs is fine with UFH but then bedrooms upstairs aren't getting enough heat but later you say the layout is the opposite with bedrooms downstairs which are too cold.

Water John

Bedrooms would be 18c, so also the general working areas of the house, sitting area 21c. Probably sized to achieve that.

Sleeper12

The system will be set up in such a way that as the outside temperature drops the heat pump works harder. It is designed to keep the upstairs at 19c. The temperature of the rads isn't important. It's the actual room temperature that is important.

It can be a little confusing when you have used gas or oil boilers all your life where the rads would be hopping, the room gets too hot and you turn heating off. Room cools & you turn heat on again. Heat pump puts out low temperature water but it is designed to be left on 24/7.

CHorn

https://www.boards.ie/discussion/comment/121476159#Comment_121476159

@ongarite no, the bedrooms were never upstairs. Just to be clear house has beds, baths, (entrance) hallway and study downstairs. That's UFH, which works fine, so every room (UFH zone) has a thermostat and the UFH system downstairs is well able to reach whatever temp we ask of it, currently set to 17, because this usually overshoots some to 18-19, the temp we'd probably all agree is best for beds/baths/halls.

Upstairs- heated by aluminum rads- is Kitchen, Living Area, TV Den, all open plan with no doors between these areas. 4 rads. Thermostat set to 20.5C and works good UNTIL temp gets to c0C (or below) at which point it struggles to get to and keep c18.

https://www.boards.ie/discussion/comment/121476747#Comment_121476747

@Water John exactly and the UFH does exactly that for the downstairs beds/baths/hallway. Actually set to 17 as we find it heats to that and then goes up a bit extra so setting for 17 gets to eventually 18-19. Study downstairs is set to 20.5c (there's one UFH zone/stat per room).

Upstairs in general working area (Kitchen, Living Room, Den) we've set stat to 20.5c, which has worked fine over the summer (we moved in in May). But now we've hit winter for the 1st time and system is struggling to get and keep 19c there working 24/7.  

https://www.boards.ie/discussion/comment/121477967#Comment_121477967

@Sleeper12 this seems to be the piece I'm missing or we're on the right track. I'm used to a rad at full throttle when cold with a gas boiler. Feeling tepid water going in to the rad- hot to touch, but not hot so you have to take your hand away, I could hold the inflow pipe forever- is what's so disconcerting.

Especially in our situation, where outside temp is 0c, thermostat is set to 20.5c and usually works, but under (sub)-zero conditions just is struggling to get to and maintain even 19 (again stat looking for 20.5) running 24/7. And my obvious solution- raise the temp of the water going into the rads- is being resisted by the builder/plumber when it seems such a simple no-brainer to me.

But looking at ALL possible solutions, short of ripping out this f^&* Joule system (support non-existent, I'm still waiting on an instructional visit to show me how it works (do they even know themselves?) or even an operating manual 6 months on, caveat emptor, however the Samsung heat pump piece seems top-notch), we have:

1) Put hotter water into the aluminium rads (my solution, maybe a non-runner if it only gets/takes low temp water).

2) Get more aluminium rads (expensive, and will it even work?).

3) Heat downstairs more to get more heat upstairs (crazy- to me- and impractical given they'd then be too hot to sleep in?).

4) Start a fire on your upstairs living area floor and/or wear extra layers of clothing in sub-zero temps outside.

But from @Sleeper12's comment "Heat pump puts out low temperature water but it is designed to be left on 24/7", is this the piece I'm missing (and the builder knows) and there's just no easy way to increase the temp in what seems the simplest solution to me (#1)? And I just have to choose between the other options?

Thanks to all of you for your help here, I've been tearing my hair out on this heating system for the best part of 2023 now.

hurikane

I have the exact same problem with a Samsung system, supplied by Joule. Your electric bills mus be massive if running 24/7. I increased the flow temp and it helped somewhat. I've also installed wood pellet stoves to bring the temperature up to a nice level when needed. Have the same issue with the cold temperatures, the heat pump struggling to to get up to temperature.

newhouse87

https://www.boards.ie/discussion/comment/121475675#Comment_121475675

How come you chose ufh downstairs? UFH would suit better to your living areas i would have thought with tiled floors etc. Bedrooms dont need to get above 19 realistically, its the living areas you want 21/22.

CHorn

https://www.boards.ie/discussion/comment/121479972#Comment_121479972

Then feel better with some of my stories (or PM me). Just for starters when they tested the system and left it running for an ENTIRE month 24/7 (while we were away) they racked up an elec bill for €800. Then we found the heat pump had never been connected to the UFH system AT ALL, so the hest pump had been running 24/7 for a month doing absolutely nothing. The test had to be completely redone. Then the stat in room a heated room b... then... (pm me if you want to feel even better with more stories or trade you)....

But how did you increase the flow temp, that seems to be the key for us here?

ongarite

Agree with above, UFH is designed for open plan living areas not bedrooms.

That rising heat in traditional house format nearly keeps bedrooms at desired temperature as a byproduct.

You will really struggle with alu rads only heating upstairs open plan living area. Raising flow rate temperature will probably double your electric bills.

Heat pump water temperature should be as low as possible to keep COP/efficiency as high as possible. This water could be 30-35c which means the alu radiators will be releasing a low heat all the time. It will feel nothing like gas or oil heating systems.

Sleeper12

For the most part with heat pumps the homeowner doesn't make any adjustments at all.

I would suggest bigger rads upstairs. They still won't get "hot" but will output more heat because they are bigger. Such a shame living area doesn't have the under floor heating & rads in the bedrooms.

There are many threads here from people who grew up with gas and oil, moved into a new home and are expected to know how their heat pump functions. I'm a big fan of Heat Pumps BUT they aren't a one size fits all that the Green Party are making them out to be. Most homes would be better suited to a hybrid heat pump /gas system

CHorn

https://www.boards.ie/discussion/comment/121479983#Comment_121479983

The house is upside-down because we wanted the views from an upstairs living area, which we did get. Upstairs living area/kitchen/den is open plan so rads made sense both from a budgetary point of view, and also because with a lot of glass there's a 'glasshouse' heating effect for most of the year (we had to keep windows open from May-September a lot of the time).

Downstairs has tiled hallway, beds, baths and study so UFH made sense there, a lot more expensive to put UFH upstairs than down with the foundations.

In a traditional setup with kitchen/living downstairs, UFH there makes sense and the heat going upstairs means you'd rarely need heat in upstairs bedrooms these days in a well-insulated house. Partly because you only want c19 in a bedroom as opposed to the 20 or so you'd want in your (downstairs) living areas so the 'bleed' from down to up covers the 19 you want up.

As I'm finding doesn't work so well in reverse- I don't want to heat my downstairs beds to higher temps- too hot to sleep in- just to 'bleed' heat to help upstairs.

Water John

Wasn't aware it was an upside down house. Larger rads upstairs would help if the HP has the capacity. Alu rads come in different heights, so it may be possible to replace them with taller rads without altering the connection points.

hurikane

https://www.boards.ie/discussion/comment/121480030#Comment_121480030

Well I feel better now seeing I'm not the only person experiencing those levels of incompetence. I've 8 zones on my system, I noticed that the heat pump was using roughly the same amount of electricity to heat one zone as it was for 3/4 zones. I'm in the process now of reducing the zones to 2 from the 8. The heat pump was kicking in for 30 mins to heat one room, the 30,mins for another, and 30 for another, and so on. The stoves were the only saving grace for me, stats now set to 19 degrees, and stoves for an hour in the evening to bring up to 22/23 degrees. I also didn't get a manual, After literally years of back and forth with Joule, I got a manual online, played around with the settings until I found sweet spot, averaging about 10kw per day now with heat pump.

newhouse87

https://www.boards.ie/discussion/comment/121480073#Comment_121480073

Fair enough but still think you have been advised badly and should have went ufh in living areas even though its upstairs. Most houses don't have heat pumps running may-september, its only from november-march really so glasshouse affect wont keep house warm them months as solar gain heat dissipates quite quickly in the dark evenings.

Your installers sound like absolute cowboys btw and i would be complaining.

newhouse87

renewableheatinghub.co.uk

Great website, helped me sort a good few problems and optimise system.

CHorn

https://www.boards.ie/discussion/comment/121480040#Comment_121480040

https://www.boards.ie/discussion/comment/121480047#Comment_121480047

Thanks again to both of you. @ongarite exactly on rising heat and the alu rads given current flow rate. Seems to me now a critical design flaw. When they designed this, they factored in the rising heat from below going up, but using temps from a traditional house setup with living areas down at c20c. Not the 17 we've got currently for bedrooms or even totally OFF in bedrooms we don't use. Up is getting nowhere enough- or any significant-'bleed' from down. And the low flow rate temp was the piece I was missing as to why the builder is resisting doing this.

Now I realize the alu rads- the 4 of them- at 30-35C, which is actually BELOW body temperature heat of 37c for a reference- are NEVER going to be able to adequately heat the upstairs living area during cold (-)0c snaps without help from one or more of (a) a higher water temp in rads (b) more rads (c) another heat source like @hurikane 's wood pellet stoves (omg has it come to that? Only a step up from my tongue in cheek option 4) or (d) heat down higher to compensate. Wow, what a nasty assortment of options!

@Sleeper12 thanks, yes, the builder looks at me with a horrified expression as though I'm a few cards short of a full deck when I say I want a manual to get to grips with the machinery (and my wife doesn't help much either with 'he likes to tinker'). Bigger rads, thanks, yes, option 2. Shame, yes as above possible critical design flaw from get-go by Joule, who just wanted to sell that heat pump++ (of course they sold us the 16kw model, but when I recalc'ed we could have managed with 8, compromised on 12). Maybe should have been rads down, ufh up or ufh for both floors.

All this really helpful in understanding the problem. I just wish that builders would talk engineering solutions to simple problems (and the problem is obvious and simple even if the solutions aren't) instead of a constant kneejerk looking for excuses as to why it (a) is not their fault (b) is someone else's problem (c) can't be done or (d) will be (a lot) extra.

newhouse87

My plumber knew zero and i mean zero about operation of heat pump. Commissioner guy came out and ran the tests and left it ons settings that were not most efficient and told me nothing, just to not alter anything. Researching myself has helped me make major improvements and that forum i linked was a godsend, some real smart guys who know everything there is to know about optimising the system. Try that, Im sure they will know your type of system and how to get it to work better. Last query, is upstirs screed floor or concrete for ufh, if it is either i would think that would also make it harder for heat below to reach air above but also since temps downstairs are 19 or less, not much heat to transfer to upstairs to add to approx 19 you already have up there.

Obvious answer is upping flow temp but will cost more.

John.G

Another point that is possibly overlooked by some is that the HP nominal output is based on a 7C/35C air/water basis and the output on at least some HPs then starts falling, you can see below that a "12kw" unit gives 11.82kw at 7C/35C, but only 7.8kw at -3C/35C and even worse at a 45C water temperature.

Water John

Since your HP is large, even possibly oversized, def bigger rads are an option. If you want you could lower the temp downstairs.

CHorn

https://www.boards.ie/discussion/comment/121480105#Comment_121480105

I'm- ahem, sigh, sob- glad to hear this has warmed (sorry!) your day. I use Emporia Vue (Gen 2) to monitor electricity so a quick check shows me averaging about 10kw/day for heat pump on a 250m2 2-storey upside-down house. So that's a useful x2 sanity check and thanks. I've left the zones at 8 for now, since we only use 1 bed, a study and a hallway downstairs (each room/area has its own zone) and the insulation is top-notch. So 2 are on and the rest just frost protection (i.e. really never unless we have visitor and extra beds get used). The ufh works great downstairs, it's just rads upstairs that's the problem.

And omg where on earth did you manage to get that priceless manuscript that is the Joule manual? That seems the holy grail of intelligent homeowners grappling with a Joule system.... Is there a link out there? Thanks.

CHorn

https://www.boards.ie/discussion/comment/121480107#Comment_121480107

Thanks so much for the link (and to your Q it's a screed floor upstairs). And yes, as you say we really only need for Nov-March, and ufh up might have been the answer. They just made the same assumptions as they would with a regular house that heat would rise, forgetting that most folks (?) prefer a colder bedroom so you're not going to get much bleed up in the upside-down house scenario.

Cowboys? I'd use another word myself, but no kidding. @hurikane, feel even better here. Joule finally set up an appointment to come show us how their magical black box worked- all singing and dancing without a user manual or written instrux apparently- one year after it was installed. So with the builder, both owners, the entire plumbing crew (3), both quantity surveyors and the architect plus assistant standing around on-site waiting for the Friday 2pm performance to start (read scheduled meeting), we got a no-show.

I wanted to tear the entire thing out just off the back off this lack of service, but (alas, sigh, sob) was persuaded otherwise. We live and learn...

hurikane

My heat pump is in a few years so is a gen 5, yours may be gen6? Got the manual here https://www.cairnhomes.com/media/kwqde4nb/joule-heat-pump-installation-manual.pdf

halkar

You should be able to set different heat curves for your ufh and rads. I am not sure if you have access to heat curves in your controller as it may need to be enabled with installer option. If commissioned properly you will have two zones in heat curves setting one for rads one for ufh. This is separate to your zones controlled by termostats. You can increase water temp for rads in there.

CHorn

https://www.boards.ie/discussion/comment/121482044#Comment_121482044

https://www.boards.ie/discussion/comment/121481993#Comment_121481993

@halkar- thanks, with information in manuals below, I'm gonna take a look at these. But given I don't have much faith in Joule at this point and a lot of this is above my pay grade, I may hire someone independent to take a look at all this. I'll see once I've digested manual below (if I can!).

Thanks a million @hurikane, using this as an example, was actually able to track down a Gen 6 version for my model Samsung AE120RXYDEG here (just Handover Document- warranty and some control panel instrux): G6 Handover Doc.indd (hubspotusercontent-eu1.net)

Also see this far more comprehensive Installation Manual here: Samsung-Gen-6-Heat-Pump-Installation-Manual-min.pdf (theunderfloorheatingcompany.co.uk)

Hopefully this will be of use to others.

loyatemu

people saying bedrooms should be 18C - yeah if you're in bed maybe. Kids and teenagers spend a lot of time in their rooms and 18C is not warm enough to be comfortable. Similarly if your wandering around your room after a shower, getting dressed etc. We have our bedrooms set to 18 overnight but 20.5 for the times of day when there are people using them.

The OPs problem is that he can't get them above 19C; if he wants to have the rooms at 23C that's his prerogative (my parents have their house at 25 the whole time, I have to start taking layers off when I visit them!). A properly designed system should be capable of doing this.

halkar

In the installation manual look under System 2 or System 4 which has details on two zone radiator and ufh configuration. There is 8c difference in flow temps as reference. I don't have Samsung hp but I have mine set min 40c. Manual has details on how to enter settings mode. You may need to increase the minimum temp for radiator zone. Temperature fluctuations between min and max are set in heat curves but not sure where it is as there is no reference to it in the manual.

You should also check the flow rate to your radiators if temperature settings are ok. If flow is slow radiators will feel cold even though hp sending hot water. If radiators are in loop they may need balancing. Manual says separate pumps for radiators and ufh but installers don't always follow manuals.

halkar

In the installation manual look under System 2 or System 4 which has details on two zone radiator and ufh configuration. There is 8c difference in flow temps as reference. I don't have Samsung hp but I have mine set min 40c. Manual has details on how to enter settings mode. You may need to increase the minimum temp for radiator zone. Temperature fluctuations between min and max are set in heat curves but not sure where it is as there is no reference to it in the manual.

You should also check the flow rate to your radiators if temperature settings are ok. If flow is slow radiators will feel cold even though hp sending hot water. If radiators are in loop they may need balancing. Manual says separate pumps for radiators and ufh but installers don't always follow manuals.

ZX7R

Hi op I had the same problem although with a completely different heating system.

Duel gas and solid fuel stove.

Long story short after having every type of plummer technician checking our heating system which was running perfectly.

It turned out to be the ventilation. Causing a cold air loop witch would drop the temperature by 4c compared to the rest of the house that was not affected.

Could worth worth thinking about.

CHorn

https://www.boards.ie/discussion/comment/121485973#Comment_121485973

No kids=no problems. So beds low temps and everyone is up and out early, no need to heat during day.

Problem is upstairs living areas (beds are downstairs) set to 20.5 struggle to get over 19 in cold snaps. 23 or 25? Lordy, no, never, that's for swimsuit fetishists or nudist colonies.

https://www.boards.ie/discussion/comment/121486141#Comment_121486141

Thanks, ventilation and insulation look sound, but I'll keep this in mind.

CHorn

https://www.boards.ie/discussion/comment/121486091#Comment_121486091

Thanks a million. Exactly along the liners of what I'm thinking. Hopefully a Joule specialist will be by sometime in 2024, we're going to try both these ideas first as simplest most obvious fix (if possible) is to raise water temp going IN to upstairs rads.

Though have to say flow seems OK as they're not cold, just the c35 as mentioned in posts here. Will check on pumps.

mickdw

You need bigger rads. No other answer really.

With low temp flows from.heat pump you need twice the rad area that you would traditionally have.

I'm no expert but I'd imagine you should be able to use the zoning to focus on bringing up temp of living areas when bedroom areas are zoned off.

Imagining a luck warm rad, it stands to reason that much more rads are needed.

halkar

You can check out this video. Not sure you have the same controller but should be similar. First setting he is doing is for the curve. Second one he is doing is for ufh. There is another setting there he didn't go into which i think it was for rads. You can check your settings without changing to see how it was configured.

https://m.youtube.com/watch?v=FcXAtVjdRE8

John.G

https://www.boards.ie/discussion/comment/121488041#Comment_121488041

If, realistically, you wont get less than 3C rad flow/return temps dT then here is what you will get at 4 different flow temps, assuming a room temperature of 20C in all cases.

(T8.5 rad) 30C/27C/3C/10% (A 1 kw rad will emit 100watts)

(T13.5 rad) 35C/32C/3C/18.2% (A 1 kw rad will emit 182watts)

(T18.5 rad) 40C/37C/3C/27.5% (A 1 kw rad will emit 275watts)

(T23.5 rad) 45C/42C/3C/37.5% (A 1 kw rad will emit 375watts)

CHorn

https://www.boards.ie/discussion/comment/121488041#Comment_121488041

Yes, 1 option- possibly the best- but a little impractical for us unfortunately with limited space and alu rads in already (under counters, along 2 walls, we'd have to increase height-wise which wouldn't look good aesthetically). Along with replace system (within warranty, my original preferred but alas past that now), increase water temp into rads, and supplement heat somehow (we have a 3-sided electric fire insert for show but does heat too).

https://www.boards.ie/discussion/comment/121488422#Comment_121488422

Really useful and thanks, could be key to getting more heat in the water going in to rads. Will check current settings.

CHorn

https://www.boards.ie/discussion/comment/121488841#Comment_121488841

Thanks, quick Q, I get the 30/27/3/% but what's T8.5 rad or T13.5 rad?

blackbox

Probably a stupid question, but if you set the upstairs room thermostat to 26 degrees, what temperature is the room at 24 hours later. This would be a way of checking if it was a control issue or a capacity issue.

John.G

https://www.boards.ie/discussion/comment/121492797#Comment_121492797

A T50 (normal rated rad) is the mean rad temperature - the required room temp, the mean rad temperature is the (flowtemp+the return temp)/2 and the required room temp is normally taken as 20C. So a T50 rad will require a flowtemp of 75C and a returntemp of 65C, (75C+65C/2 = 70C, 70C - 20C =50C so a T50 rad. The above rad (30+27)/2 - 20, = 8.5C so a T8.5 rad. Rad output is exponential (to the power of 1.3) so a T8.5 rad will give (8.5/50)^1.3 x100 = 10% (of a T50 rad). and so on.

CHorn

https://www.boards.ie/discussion/comment/121492856#Comment_121492856

Only a problem when outside temps approach 0. Temp upstairs is set to 20.5, and works fine, EXCEPT when outside temps get real cold (0), then the rads even on 24/7 struggle to maintain c19. So definitely a capacity issue as discussed above, nothing wrong with the controls, though as has been pointed out we can try to change the controls to get hotter water into the rads.