MVHR and cooling

[-rick-]

2 minutes ago, flanagaj said:

Excuse my ignorance on this, but I thought ASHP grants are only available to individuals switching from conventional oil/gas to ashp and not for individuals building a new home?

 

It's available to self-builders too. Search the forum, plenty of examples.

[Pendicle]

Not in Scotland unfortunately they stopped for new builds last August 

[joth]

18 hours ago, -rick- said:

 

You can get the BUS grant to install a water based ASHP (including the cost of fancoils if you want). Have to be careful as lots of MCS installers around bumping up the costs to suck up the grant and more. But plenty of experience on here. If you are careful and have UFH downstairs then won't need many fancoils and should be able to keep the costs close to the grant amount so the system will be free or almost free.

 

Referring back to my previous post and your tight budget. The more different things you need, the more quotes you need, the more contractors you involve, all adds drain on your time and the more likely you will get overwhelmed dealing with so many things. When that happens the chances of costly mistakes goes up. Try to keep things as simple as possible. Fewest components, minimal complexity.

If you can get multiple FCUs installed along with the ashp and uvc and come in under the grant, then you're doing very well.

I was quoted £8k for supply and install of a single (ducted) FCU! Obviously I didn't pay that 

If you're happy with wall hung FCU with no condensation drain then it maybe more achievable; plenty of success reports from that approach appearing now. (As well as much easier to source, wall hung are easier to install and to control. But ugly and noisy in comparison)

 

if you're DIY installing, no grant, then single ashp is going to be cheaper. 

If you're paying for professional install, (in price hiking south of the country) and already maxing out the grant on the a2w, then adding on an a2a is probably comparable price to adding additional FCU. Especially if going for ducted installs. 

[Dave Jones]

you can diy and get the grant, just need the company who supply the kit to sign it off. thats what we did.

 

 

[-rick-]

37 minutes ago, joth said:

If you can get multiple FCUs installed along with the ashp and uvc and come in under the grant, then you're doing very well.

I was quoted £8k for supply and install of a single (ducted) FCU! Obviously I didn't pay that 

If you're happy with wall hung FCU with no condensation drain then it maybe more achievable; plenty of success reports from that approach appearing now. (As well as much easier to source, wall hung are easier to install and to control. But ugly and noisy in comparison)

 

It would admittedly be tricky to find a company to do it all for you within the grant. But more self directed options exist like Cool Energy that you could likely get pretty close to fully covered by the grant. Yes I was thinking of the radiator replacement/wall hung units. Surprised you say they are noisy, as people on here who've got them say they are pretty silent. Personally I'd be more worried about ducted ones transmitting noise between rooms.

 

I'm a light sleeper so personally I wouldn't want any fans running when I'm trying to sleep (I notice even 'silent' ones), but I'd hope in a well built modern house if you control the temperature of the structure during the day then the room should carry through the temperature while sleeping without the unit needing to run.

 

If installing FCUs in a new build at least with a decent amount of DIY labour I don't see why you wouldnt want to run pipes for condensate drains and insulate the pipes well. It's a something you could do DIY following behind a plumber to if you didn't want to do the plumbing yourself (tell the plumber to use preinsulated MLCP and just deal with the junctions). If the FCUs are fully ready for below dew point operation then in the event that a mistake was made in the design and you need more cooling than planned then you always have the option to modify the system to support below dew point feeds to the FCUs (with some changes in the plant room and the tradeoff of slightly lower efficiency). Would suggest you want to size the system to cover heating/cooling needs without operating below dew point though.

 

37 minutes ago, joth said:

 

if you're DIY installing, no grant, then single ashp is going to be cheaper. 

If you're paying for professional install, (in price hiking south of the country) and already maxing out the grant on the a2w, then adding on an a2a is probably comparable price to adding additional FCU. Especially if going for ducted installs. 

 

You'd have to sequence this carefully though as it would be violating the BUS grant. MCS wouldn't install if the AC system was already there and MCS might not want to install anything if they can't satisfy themselves that you have provided adequate heating for all rooms (which you might not if it depends on the a2a system). You would also need planning permission for the a2a system. My thought is if you are going a2a, go the whole way and just do an a2a system (they can heat as well) and rely on immersion HW heating using solar/cheap rate. Don't do both.

Edited July 16 by -rick-
Mention HW + preinsulated pipe

[JohnMo]

7 minutes ago, -rick- said:

My thought is if you are going a2a, go the whole way and just do an a2a system (they can heat as well) and rely on immersion HW heating using solar/cheap rate. Don't do both.

I would concur with that, why dick about with two systems. If you wanted cheaper DHW you could do a heat pump cylinder.

 

 

[joth]

6 minutes ago, -rick- said:

I'd hope in a well built modern house if you control the temperature of the structure during the day then the room should carry through the temperature while sleeping without the unit needing to run.

This is exactly not my experience (Enerphit passive house). Heating you can batch input, a few hours will allow the building to coast through the day. But cooling needs applying in the occupied room, when it is occupied.

We sleep with the door and window closed (for noise control), and a couple humans output enough heat to cause the room to overheat even in winter.

9 minutes ago, -rick- said:

Surprised you say they are noisy, as people on here who've got them say they are pretty silent. Personally I'd be more worried about ducted ones transmitting noise between rooms.

 

I said noisy in comparison. I have ducted unit so can't directly compare, but the ducted unit is near silent - no noisier than MVHR - unless running at full tilt.

 

10 minutes ago, -rick- said:

I don't see why you wouldnt want to run pipes for condensate drains and insulate the pipes well.

Indeed, I ran the condensate pipe anyway as why not. My point was if paying someone else to install, forgoing this will help eek in under the grant cap.

 

11 minutes ago, -rick- said:

MCS wouldn't install if the AC system was already there

If the BUS funded ASHP is sufficient size to supply all the whole property heating needs, and the AC is there purely to supply the cooling needs (which MCS don't cover in their design guidance anyway) then logically there's no conflict. What the installer and/or someone arbitrating the legislation would rule I don't know.

 

 

 

[joth]

37 minutes ago, JohnMo said:

I would concur with that, why dick about with two systems. If you wanted cheaper DHW you could do a heat pump cylinder.

 

 

As a counter point - I did the single ASHP with heating and cooling system in my own home, and overall it required more dicking about than the two separate systems I've setup controls for in other homes.

Admittedly, I did mine in 2020 when there was less information available on how to do it. (And, global events were making doing anything more difficult lol)

So on balance, if doing it again then I'd do the same (single ashp) using the knowledge I'd gained.

But if advising a friend (who isn't technical / isn't going to be hands on in the install) I'd probably advise separate systems unless I'm happy to hand-hold them through the whole process 

 

Edited July 16 by joth

[-rick-]

22 minutes ago, joth said:

This is exactly not my experience (Enerphit passive house). Heating you can batch input, a few hours will allow the building to coast through the day. But cooling needs applying in the occupied room, when it is occupied.

We sleep with the door and window closed (for noise control), and a couple humans output enough heat to cause the room to overheat even in winter.

 

Well this sent me down a little rabbit hole with Copilot. Not worth muddying this thread with that though as I think the main point is as long as the system is quiet enough to sleep through any system (water or refrigerant) would work well to offset this. For me personally this pushes me towards wanting UFH for cooling in the bedrooms too to avoid fans running overnight as I'm particularly sensitive to that.

 

22 minutes ago, joth said:

If the BUS funded ASHP is sufficient size to supply all the whole property heating needs, and the AC is there purely to supply the cooling needs (which MCS don't cover in their design guidance anyway) then logically there's no conflict. What the installer and/or someone arbitrating the legislation would rule I don't know.

 

I feel out of my depth talking about this more so I will let others address this. Either way, planning permission is still an issue.

[joth]

36 minutes ago, -rick- said:

For me personally this pushes me towards wanting UFH for cooling in the bedrooms too to avoid fans running overnight as I'm particularly sensitive to that

Also have a look at radiant panel cooling. Like FCU this is popular on the continent but less so in the UK. But apparently works very well for fanless cooling. 

 

37 minutes ago, -rick- said:

Either way, planning permission is still an issue.

Happily this has recently been relaxed for detached houses. 

Physically finding space for two outdoor units can be a pita though, a definite benefit of going single unit.

[-rick-]

13 minutes ago, joth said:

Also have a look at radiant panel cooling. Like FCU this is popular on the continent but less so in the UK. But apparently works very well for fanless cooling. 

 

Noted thanks.

 

13 minutes ago, joth said:

Happily this has recently been relaxed for detached houses. 

Physically finding space for two outdoor units can be a pita though, a definite benefit of going single unit.

 

Not for systems used exclusively for cooling AFAIK. If you get an A/C system that can heat then you have the issue with BUS.

[JohnMo]

30 minutes ago, joth said:

look at radiant panel cooling

A link

https://www.solray.co.uk/effective-and-efficient-cooling/

[JohnMo]

49 minutes ago, joth said:

look at radiant panel cooling

A link

https://www.solray.co.uk/effective-and-efficient-cooling/

 

https://www.variotherm.com/en/products/modular-wall-heatingcooling/technical-information.html

[-rick-]

5 minutes ago, JohnMo said:

https://www.variotherm.com/en/products/modular-wall-heatingcooling/technical-information.html

 

These look good. I quite like the idea of hidden emitters as part of a wall. If DIYing likely loads cheaper than fancoils too (though with some likely downsides)

Edited July 16 by -rick-

[JohnMo]

A DIY approach could UFH gypsum boards attached to wall, fit pipe and plaster finish. Floor finish can be carpet etc.

[Wil]

I’ve always wondered about this DIY approach with the routered boards on the wall and plaster over UFH pipes. Not quite been brave enough to try it at my place though 😞

[JohnMo]

1 hour ago, Wil said:

I’ve always wondered about this DIY approach with the routered boards on the wall and plaster over UFH pipes. Not quite been brave enough to try it at my place though 😞

Could imagine coming to a pool of water, and a new picture on the wall. And then getting the blame for it. Who's stupid idea was to put heating in the wall.

[Wil]

On 17/07/2025 at 13:03, JohnMo said:

Could imagine coming to a pool of water, and a new picture on the wall. And then getting the blame for it. Who's stupid idea was to put heating in the wall.

 

Yep, pretty much exactly that! Sort of limits furniture placement too.

[LnP]

Can anybody recommend a good way to calculate cooling load? There are a few tools on t'internet, but it seems to be more complicated than heat loss.

[Nick Laslett]

7 hours ago, LnP said:

Can anybody recommend a good way to calculate cooling load? There are a few tools on t'internet, but it seems to be more complicated than heat loss.

You can calculate cooling loads in LoopCAD. 
 

 

You can use it free for 30 Days. 
 

Link is to page of tutorial videos. There is a 14mins video on how cooling loads work in the software. Watch video see if it makes sense. 
 

https://www.avenir-online.com/AvenirWeb/support/tutorial/?productLine=loopcad

 

Edited July 22 by Nick Laslett

[Nick Laslett]

Not used these guys software. 
 

https://www.h2xengineering.com/blogs/cooling-load-calculation-essential-guide-mechanical-engineers/#

 

But their blog article covers the topic in a lot of detail.  There is a video here too. 
 

Also found this simple rule of thumb method. 
 

https://www.calmec.co.uk/blog/understanding-heating-and-cooling-load-calculations/#

 

The process of working out load calculations is the following:

 

1. Determine the square footage of the space you are looking to heat or cool  

 

2. Divide the footage by 500  

 

3. Multiply that figure by 12,000 to get the space cooling load  

 

4.Add around 380 Btu per person within the building and 1,200 Btu for every kitchen 

 

5.Add 1000 Btu to account for solar radiation through windows 

 

6. Convert the final number into tonnes by dividing it by 12,000

 

This is all in imperial measurements. 

Edited July 22 by Nick Laslett

[SteamyTea]

10 hours ago, Nick Laslett said:

Multiply that figure by 12,000

 

10 hours ago, Nick Laslett said:

dividing it by 12,000

Really.

 

Is that tons of refrigerant?

1 ton = 3.5 kW.

[NCXo82ike]

On 16/07/2025 at 09:34, -rick- said:

 

It would admittedly be tricky to find a company to do it all for you within the grant. But more self directed options exist like Cool Energy that you could likely get pretty close to fully covered by the grant. Yes I was thinking of the radiator replacement/wall hung units. Surprised you say they are noisy, as people on here who've got them say they are pretty silent. Personally I'd be more worried about ducted ones transmitting noise between rooms.

 

I'm a light sleeper so personally I wouldn't want any fans running when I'm trying to sleep (I notice even 'silent' ones), but I'd hope in a well built modern house if you control the temperature of the structure during the day then the room should carry through the temperature while sleeping without the unit needing to run.

 

If installing FCUs in a new build at least with a decent amount of DIY labour I don't see why you wouldnt want to run pipes for condensate drains and insulate the pipes well. It's a something you could do DIY following behind a plumber to if you didn't want to do the plumbing yourself (tell the plumber to use preinsulated MLCP and just deal with the junctions). If the FCUs are fully ready for below dew point operation then in the event that a mistake was made in the design and you need more cooling than planned then you always have the option to modify the system to support below dew point feeds to the FCUs (with some changes in the plant room and the tradeoff of slightly lower efficiency). Would suggest you want to size the system to cover heating/cooling needs without operating below dew point though.

 

 

You'd have to sequence this carefully though as it would be violating the BUS grant. MCS wouldn't install if the AC system was already there and MCS might not want to install anything if they can't satisfy themselves that you have provided adequate heating for all rooms (which you might not if it depends on the a2a system). You would also need planning permission for the a2a system. My thought is if you are going a2a, go the whole way and just do an a2a system (they can heat as well) and rely on immersion HW heating using solar/cheap rate. Don't do both.

After spending too long thinking I'd get the comfopost, with advice from many on this thread it's clear to me at least that the actual cooling from it is very limited and not worth it. 

 

Seems reasonable to me to run UFH for heating wherever possible, giving some cooling ability, then also run pre-insulated pipe on a second zone that could supply FCUs at under dew point if needed. Plus condensate drain runs. Then FCUs can be added as needed. Cheap on AliExpress with the usual caveats. The Jaga units are available in the UK with warranty but are around £900 each. Depending on house type, a more economical strategy could be a mix, e.g. UFH downstairs and FCUs in the rooms that overheat, or bedrooms where a low temp may be most important. 

 

I do reckon a dual UFH and FCU setup could be quite neat however. Most of the time you get the lovely heat of UFH. If it's really cold and you want to keep a low flow temperature, bring the FCUs on board for additional heat output. If you want to get the place warm fast (returning from holiday etc), bring the FCUs on board. You can then do gentle cooling, but add on the FCUs as needed. And you can use FCUs at below dew point to dehumidify as needed. 

 

The Panasonic Aquarea units can drive two separate zones at different temperatures. I guess if one loop has only a few FCUs on it it may need a volumiser/buffer.

[NCXo82ike]

I also see how just putting a multi-spilt in, supplemental to whatever heating you have, could make sense- particularly if you have a good place to put the outdoor unit. In a mid-terrace in a conservation zone we're hiding our heat pump at the end of the garden, and avoiding an additional outdoor unit is valuable.

 

Or as suggested: having an A2A heat pump to include cooling, then an alternative solution for DHW (heat pump cylinder, sunamp etc) would be really neat. That's what I've suggested to my sister in an overheating top floor flat, should the BUS not be so twitchy about cooling

 

[SBMS]

53 minutes ago, NCXo82ike said:

I also see how just putting a multi-spilt in, supplemental to whatever heating you have, could make sense- particularly if you have a good place to put the outdoor unit. In a mid-terrace in a conservation zone we're hiding our heat pump at the end of the garden, and avoiding an additional outdoor unit is valuable.

 

Or as suggested: having an A2A heat pump to include cooling, then an alternative solution for DHW (heat pump cylinder, sunamp etc) would be really neat. That's what I've suggested to my sister in an overheating top floor flat, should the BUS not be so twitchy about cooling

 

We discounted a2a for heating after a couple of AC contractors said that they wouldn’t have it for heating over UFH as it just isn’t as nice. 
 

I was planning on UFH downstairs and AC upstairs for cooling and supplementary heating but am now thinking more of fan coils and using the heat pump for cooling…