Struggling to heat first floor with retrofit ASHP and underfloor heating

[MrNormo]

Hi everyone,

 

I've been lurking on these forums over the past two years and have picked up many tips along the way. I do have some issues of my own now.

 

I have a LG Therma V 12kW ASHP along with a UFH manifold on the ground floor in screed, and another using boards on the first floor. We're using the AI mode on the ASHP which is currently floating around 48-50c based on outside temperature hitting the minuses.

 

The ground floor has been fantastic this winter. Laughing at the outside temperature changes and seems to be holding heat at an acceptable rate too.

 

The first floor, which is carpeted, is struggling big time. We have set a modest 17c average and we're struggling to hit that set point. The carpet shows a surface temperature of 24-25c which is around 5-6c off what the ground floor is hitting.

 

As a result, the heating has been on 24/7 during the cold spell this week and I'm seeing figures such as £18 a day in electricity as of this week! 

 

I can think of several causes for this issue

 

1- The underlay and carpet on the first floor isn't as effective as the tile and wood flooring on the ground floor. There's also a 5mm layer of ply on top of the board subfloor. 
2- The boarding system isn't as good as in-screed at scrubbing off heat. There is also far less floor space on the first floor.
3- Unlike the ground floor with it's XPS insulation, heat may travel both directions on the first floor.

 

I've thought of some options. Some more radical than others.

 

1- Look at alternative heating methods on first floor. This could involve replacing the first floor system with something more effective, at great cost and disturbance
2- We remove carpet and lay wood flooring. This isn't ideal as we wanted a cosy bedroom
3- We retrofit MVHR, which can take heat from 2 of the rooms in the ground floor and 'share the cold' from the first floor. We could also install a post-heater into our first floor manifold for a boost.

 

Has anyone got any advice or other ideas on this? I've been thinking about it for a while and I'm really struggling.

 

I touched on it earlier, but the insulation is at 300mm in the loft, cavity walls filled with ecobead platinum and ground floor slab with XPS insulation with screed on top.

 

Here is a good representation of the first floor heating situation. We dropped the thermostat down just before midday to give the heat pump a break but it didn't take long to kick in again

 

 

Here is the ground floor, showing how it should be done

 

 

Appreciate all your help in advance.

 

Thanks,
Oli

[ReedRichards]

Heat has to go somewhere and the heat from UFH on the first floor must surely stay inside the house unless you have a severe problem with drafts.  So I don't see there is necessarily any link between your cold first floor and the amount of electricity you are using.  However if you have UFH throughout you surely cannot need a water flow temperature of 50 C, wouldn't 40 C or less suffice?  Reducing the flow temperature to as little as you can will pay dividends in cutting your electricity use.    

Edited January 19, 2023 by ReedRichards

[MrNormo]

Hello ReedRichards,

 

Thanks for the reply. For the ground floor, a 40c flow rate would be fine but we see zero temperature change on the first floor if we do this. 

 

We didn't insulate under the UFH boards when installing, so I fear the heat is going down to the ground floor / ceiling void and not up. 

 

Thanks,

Oli

[ProDave]

What is the context?  New build?  Retro fit in old house?  Insulation levels etc?

 

And your approximate location so we get an idea how cold it is?

[MrNormo]

Hi ProDave,

 

It's a retro fit in an old house build approx '68 - '70. We stripped it right back and did a re-wire, asbestos removal, door/window replacement etc. 

 

The property is a strange shape, with one large sloped roof on one side and a smaller one on the other. Half of the first floor has a loft above it (left on the below pic). The fact these rooms stay warm and get to temp quick is what makes me think it's a first floor heating issue through the carpet.

 

 

Insulation wise, I covered off in the original post but is there anything else I can give to help?

 

Quote

I touched on it earlier, but the insulation is at 300mm in the loft, cavity walls filled with ecobead platinum and ground floor slab with XPS insulation with screed on top.

 

EDIT: Forgot location. We're near Portsmouth which has been fitting -2 to -5 this week

 

Thanks,

Oli

Edited January 19, 2023 by MrNormo
Forgot location

[Conor]

I think you've summed it up well, lots of heat going down in to the ceiling void and then going tho knows where. 

 

Was the carpet and underlay rated for UFH? We have that and heat transfer isn't an issue.

 

MVHR won't make a difference, all extract air goes out the building through the heat exchanger and then fresh air in to the house... So the air tha is distributed is slightly cooler than the average temp of the extracted air. So want warm anything 

[ProDave]

It looks like at least part of your upper floor is above the garage?

 

While heat going down from upstairs into a room below would not be "wasted" any such heat going downwards into the garage would be.  Also with that portion of the upper floor above a garage, it is likely there will be air paths due to leaks etc allowing the cold air from the garage to the inter floor space.

 

I suspect the solution lies with taking it all up again and doing it properly, making sure the entire ceiling above the garage is properly air tight sealed and properly insulated, then re fit the UFH.

 

With carpet is is likely you will need the UFH pipes closer together than the downstairs UFH.

 

Probably not what you want to hear.

[MrNormo]

6 minutes ago, Conor said:

I think you've summed it up well, lots of heat going down in to the ceiling void and then going tho knows where. 

 

Was the carpet and underlay rated for UFH? We have that and heat transfer isn't an issue.

 

MVHR won't make a difference, all extract air goes out the building through the heat exchanger and then fresh air in to the house... So the air tha is distributed is slightly cooler than the average temp of the extracted air. So want warm anything 

 

We had a good stab what what we thought was right for the carpet. The layering goes

 

Carpet (1.70 tog)

UFH Underlay (0.75 tog)

5mm ply

UFH Boards with reflectors

 

Good point on MVHR - I was half hoping with intake / extract ducts on the ground floor that this may distribute the heat more evenly in rooms struggling to heat?

[Nickfromwales]

In this type of dwelling, the 1st floor joist voids will be notorious for ventilation heat loss aka drafts. 
I’m afraid all the heat is likely getting literally sucked out of there by the joists bring cut into the internal leaf of the block wall. 
This may have been refurbished with a not-so-good eye in terms of accepting UFH as the only heat emitters. 
The carpets are your enemy also, could you accept a bonded, engineered wooden floor up there, at least in the worst affected rooms? ( eg leave the landing carpeted ).

 

Exactly which product was used and exactly how was it installed for the 1st floor? 

[Nickfromwales]

3 minutes ago, MrNormo said:

- I was half hoping with intake / extract ducts on the ground floor that this may distribute the heat more evenly in rooms struggling to heat?

Not a chance sorry. 

[MrNormo]

4 minutes ago, ProDave said:

It looks like at least part of your upper floor is above the garage?

 

While heat going down from upstairs into a room below would not be "wasted" any such heat going downwards into the garage would be.  Also with that portion of the upper floor above a garage, it is likely there will be air paths due to leaks etc allowing the cold air from the garage to the inter floor space.

 

I suspect the solution lies with taking it all up again and doing it properly, making sure the entire ceiling above the garage is properly air tight sealed and properly insulated, then re fit the UFH.

 

With carpet is is likely you will need the UFH pipes closer together than the downstairs UFH.

 

Probably not what you want to hear.

 

Part of the fun of retrofitting! I'd rather someone tell it to be straight and I've often come across your advice in previous research, so thanks for your reply.

 

We did stuff as much rockrool as we could with the room floating over the garage. That's the only floor space that is insulated but appreciate the garage is still very cold and that will have an impact. The garage itself has a plastered ceiling but that doesn't take away from the air paths point you mentioned. 

 

For what it's worth, I wasn't very happy with the company who installed the heating on the first floor. I did do research at the time but having done more research, reflectors just aren't very effective at this application. 

[MrNormo]

6 minutes ago, Nickfromwales said:

In this type of dwelling, the 1st floor joist voids will be notorious for ventilation heat loss aka drafts. 
I’m afraid all the heat is likely getting literally sucked out of there by the joists bring cut into the internal leaf of the block wall. 
This may have been refurbished with a not-so-good eye in terms of accepting UFH as the only heat emitters. 
The carpets are your enemy also, could you accept a bonded, engineered wooden floor up there, at least in the worst affected rooms? ( eg leave the landing carpeted ).

 

Exactly which product was used and exactly how was it installed for the 1st floor? 

 

Thanks for the info and makes sense! 

 

A engineered floor is on the consideration list here. We have it on the ground floor and it has no issues getting the rooms to temperature.

 

The system we have in place is this stuff, at 200mm spacing

https://www.lksystems.se/en/products/floor-heating/laying-procedures/joist-systems/lk-heatfloor-22-slotted-board-22246450

 

Thanks,

Oli

[Temp]

Any chance you could roll up the carpet and underlay in one room to see what happens?

[Nickfromwales]

15 minutes ago, MrNormo said:

I'd rather someone tell it to be straight

That UFH system is “less than suitable”. 

 

 

 

 

 

 

 

 

 

 

 

There…..I didn’t say “bag of shit”. Gold star for Nick  

[MrNormo]

3 minutes ago, Nickfromwales said:

That UFH system is “less than suitable”. 

 

 

 

 

 

 

 

 

 

 

 

There…..I didn’t say “bag of shit”. Gold star for Nick  

 

😂

 

Assuming we're lifting it all and trying again, what would be the recommendation here? 

 

Thanks

[MrNormo]

5 hours ago, Conor said:

I think you've summed it up well, lots of heat going down in to the ceiling void and then going tho knows where. 

 

Was the carpet and underlay rated for UFH? We have that and heat transfer isn't an issue.

 

MVHR won't make a difference, all extract air goes out the building through the heat exchanger and then fresh air in to the house... So the air tha is distributed is slightly cooler than the average temp of the extracted air. So want warm anything 

Hi Conor,

 

Which floor is the carpet on? Can you let me know what system you used? 

 

Thanks

[Conor]

23 minutes ago, MrNormo said:

Hi Conor,

 

Which floor is the carpet on? Can you let me know what system you used? 

 

Thanks

I can't remember, partner took care of it. All I remember is it cost twice as much as normal underlay!

 

It might sound drastic, but you could look in to putting insulation in your celing void and doing some filling work where the joists enter the external wall. You might end up with a lot of ceilings to patch up and paint, but you'll reduce you heat loss and get more out of your UFH.

[Nickfromwales]

17 hours ago, MrNormo said:

 

😂

 

Assuming we're lifting it all and trying again, what would be the recommendation here? 

 

Thanks

Probably OSB trays with pipes laid in a pug ( biscuit ) mix screed @ProDave may have detailed this on his blog(?).

If too intrusive, you could use aluminium spreader plates.

The focus on detailing here needs to be about making the void 'warmer' and less drafty, so fully filling the width with PIR and foaming the gaps will be a good place to start. I fear this system is currently wasting a LOT of the available heat energy keeping these layers of wood warm, with little then left to rise upwards as space heating.

 

The installer hasn't looked into this properly, and therefore hasn't mitigated against these associated ( accumulative ) losses when working out what's needed.

 

You could go back to rads upstairs, but they'd need to be huge.   

[Dave Jones]

heatloss calcs from from the designer of the system ?

 

actual heatloss ?