Low temperature hydronic (underfloor) cooling - heat pump sizing.

[Luk88]

I have a rather small house (even for European standards - 95m2) that is being heated in winter by low temp hydronic underfloor system powered by a wood pellet burner. I'm happy how it works in winter and the cost to heat is reasonable as the house is well insulated. Depending on how cold or warm the winter is I burn 1.5~2.5 tons of coniferous pellets per season.

But, summer heat is getting quite bad as I work 100% from home and I use powerfull PCs that make my "office" even hotter. So I started looking into air-water heat pumps for the purpose of underfloor cooling. As I'll have excess power during the summer once I install my next batch of panels.

There are various online heat pump heating calculators that claim I should be fine with a 6kW heat pump. But there are none I can find for cooling(at least focused on my climate and local building methods).

I've done quite a bit of research and I came to a conclusion I need an 8kW split R32 unit for cooling (R32 because r290 is still too expensive, split, because I plan to switch it off in winter without risk of freezing so no monoblock). I decided to get TCL's (rebadged Chinese product that is no doubt sold under different names everywhere) with a model number of THF -8D/HBpO-A. One of the reasons is the compact indoor unit. I'll still use my electric tankless water heater for hot water as I have no space for a hot water tank.

But I'm having second thoughts if this is the best (budget!) choice so I decided to ask the forum. I'm getting the unit for $2500 and I'll do 90% of the install myself.

Anyone here who uses underfloor hydronic cooling? What are some pitfalls to avoid (other than condensation).

 

[hwy17]

Wouldn't a mini split high wall unit be easier? You say aside from condensation, but that's the entire downside at hand here.

Also cool air falling from a high wall is preferable imo. Opposite of their downsides for heating.

 

[Luk88]

Wouldn't a mini split high wall unit be easier? You say aside from condensation, but that's the entire downside at hand here.

Also cool air falling from a high wall is preferable imo. Opposite of their downsides for heating.

I had to look up what is a "high wall" unit. It is a classic system with a unit that sits on a wall (usually quite high up) and emits cool air into the room.

I should've mentioned in my original post I've avoided classic air-con in this house for last 6 years because I didn't want to tear up the walls.

The climate here doesn't feel very humid in the summer (at least in comparison with the UK I lived in before). I had a look at few websites that claim dew point is around 12C~15C around here in the summer. If I could keep the floor at 18~20C that could hopefully work.

Perhaps there isn't much info about it precisely because it doesn't work? I guess I'll find out after the install.

 

[Zwy]

I have a rather small house (even for European standards - 95m2) that is being heated in winter by low temp hydronic underfloor system powered by a wood pellet burner. I'm happy how it works in winter and the cost to heat is reasonable as the house is well insulated. Depending on how cold or warm the winter is I burn 1.5~2.5 tons of coniferous pellets per season.

But, summer heat is getting quite bad as I work 100% from home and I use powerfull PCs that make my "office" even hotter. So I started looking into air-water heat pumps for the purpose of underfloor cooling. As I'll have excess power during the summer once I install my next batch of panels.

There are various online heat pump heating calculators that claim I should be fine with a 6kW heat pump. But there are none I can find for cooling(at least focused on my climate and local building methods).

I've done quite a bit of research and I came to a conclusion I need an 8kW split R32 unit for cooling (R32 because r290 is still too expensive, split, because I plan to switch it off in winter without risk of freezing so no monoblock). I decided to get TCL's (rebadged Chinese product that is no doubt sold under different names everywhere) with a model number of THF -8D/HBpO-A. One of the reasons is the compact indoor unit. I'll still use my electric tankless water heater for hot water as I have no space for a hot water tank.

But I'm having second thoughts if this is the best (budget!) choice so I decided to ask the forum. I'm getting the unit for $2500 and I'll do 90% of the install myself.

Anyone here who uses underfloor hydronic cooling? What are some pitfalls to avoid (other than condensation).

It will condense humidity on the floor. If you live in the desert, it wouldn't be a problem. Where I live in the Midwest USA, the dewpoints hit 70°F so it gets quite sticky. If I open my shop doors, the cement floor will sweat badly and this then adds to the indoor humidity as the cement warms up and the water evaporates.

I read the other post and you mentioned tearing up the walls but with a mini split you only need one hole to run the lines and one electrical cord thru. If you mount high up on the wall the hole can be close to the eave so rain won't enter easily. I have mounted a floor model and a wall hanger but both holes were down low and I just use a vinyl siding trim box where the holes went with proper flashing. I did the same with the ac disconnect.

What is your house construction? ICF walls for example, the lines can be run into the attic space. This would require the drain hose to have a pump unless you have a way to drain it in the interior.

If there is much summer humidity in your area, the infloor cooling will not work out well, possibly leading to mold.

 

[Luk88]

It will condense humidity on the floor. If you live in the desert, it wouldn't be a problem. Where I live in the Midwest USA, the dewpoints hit 70°F so it gets quite sticky. If I open my shop doors, the cement floor will sweat badly and this then adds to the indoor humidity as the cement warms up and the water evaporates.

No, not a desert. When I lived in the UK, there there were few very hot summers, but it was always hot and humid - to the point my bamboo window shades were getting moldy with no aircon. Here (in the part of Poland I'm in) it seems it is either cold and wet or hot and dry - still not desert dry.

I have this condensation problem in my basement which has walls at ~2C-5C(35-40F).

Condensation may well happen, but I hope it will be rare and it will still mean the system is usable (let's say I can increase the temp from 20C (68F) to 24C (75F) - it is still a lot better than 30C(86F indoors). On the other hand I never had condensation in my house even when a heatwave hits while the house is relatively cold (let's say the house is at 20C(68F) - then suddenly we have 35C(95F) in the shade outside. It takes about a week for the floors to heat up). This seems to support the idea the dew point is usually well below 20C.

The choice isn't so much a high wall unit vs hydronic. It is hydronic or nothing. I explain more about why below.

I read the other post and you mentioned tearing up the walls but with a mini split you only need one hole to run the lines and one electrical cord thru. If you mount high up on the wall the hole can be close to the eave so rain won't enter easily. I have mounted a floor model and a wall hanger but both holes were down low and I just use a vinyl siding trim box where the holes went with proper flashing. I did the same with the ac disconnect.

This is every room, right? Also, not every room has space to mount a wall unit on an external wall where an outdoor unit could sit. So we're talking about many sections of horizontal piping inside and outside.

What is your house construction?

The main structure is a ceramic cavity block called porotherm (it is impossible to carve, it shatters when hit sufficiently hard to break it, it has to be cut with diamond tools to groove it). Inside there is about an inch of "traditional plaster". This is a sand based plaster that is very brittle. If I started grooving porotherm under probably 2~3 inches above and below would fall off.
Outside there is graphite styrofoam 10in of it (glued with a half inch cavity between it and porotherm). On the outside of the styrofoam there is a glass fiber mesh in about half inch of a kind of plaster/glue and on top of tgat there is finally exterior (textured) plaster.

Interior walls are either same material as outside (load bearing) or 5in porous concrete (with same traditional plaster).

Also, where there is no plaster (in the staircase/corridor) there is stone panels on the walls.

So, just punching to the outside is definitely possible, but in many places 2-3m of horizontal section would be needed and you can't hang an outdoor unit on styrofoam so each outdoor unit would need to be at ground level adding a vertical section too. Just thinking about all this work,and how much plastering, grooving it needs (and will still probably not look very good outside and require substantial furniture changes inside). It makes me think the heat is not that bad after all

So in anticipation of problems I started this thread. Condensation is definitely going to be a concern, but I hope it will only limit the usefulness of the system somewhat. Not make it useless.

ICF walls for example, the lines can be run into the attic space. This would require the drain hose to have a pump unless you have a way to drain it in the interior.

I do have drainage access in the attic, this would help at least on the upper level of the house.

If there is much summer humidity in your area, the infloor cooling will not work out well, possibly leading to mold.

The key question is, is there too much? I'll definitely not let it get moldy. If I see any condensation ill have to raise the temperature.

 

[Supervstech]

In floor hydronic heating works for several factors, hot air rising, and radiant transfer, along with warm feet comfort.

Hydronic in floor cooling has a different issue. You can gain cool floor comfort for the feet, but, the floor is a negligible heat gain to the structure. The walls and ceiling are the main contributors… for cooling to work, you would need to loop all heat gain surfaces to the system.

Or just, you know, cool the air in the space, with an air handler…

 

[OzSolar]

Plus one vote for a mini-split. I've been in a few buildings that experimented with radiant cooling. During the summer they struggled with humidity and that was with supplemental dehumidification which to me looked a lot like DX air conditioning. It was still uncomfortable humid in the building.

Have you bumped into cooling with solar thermal panels? It's a form of Radiative Cooling.

It's said that 2,000 years ago the Persians were able to make ice in the dessert with this technique. I wasn't there so I can't vouch, just barely missed it.

Today we do it to cool our residential swimming pools, particularly the above ground style. As the hot summer goes on they turn into bath water. Most solar pool controllers have a circulate at night function.

For several years now I've been daydreaming about putting several hundred square feet of solar thermal panels into my shop's radiant in-floor heating system to experiment with it. Almost no chance of cooling down to dew point and if it did it wouldn't be a big deal.

Snipped from energy.gov.

 

[wpns]

No, not a desert. When I lived in the UK, there there were few very hot summers, but it was always hot and humid - to the point my bamboo window shades were getting moldy with no aircon. Here (in the part of Poland I'm in) it seems it is either cold and wet or hot and dry - still not desert dry.

I have this condensation problem in my basement which has walls at ~2C-5C(35-40F).

Condensation may well happen, but I hope it will be rare and it will still mean the system is usable (let's say I can increase the temp from 20C (68F) to 24C (75F) - it is still a lot better than 30C(86F indoors). On the other hand I never had condensation in my house even when a heatwave hits while the house is relatively cold (let's say the house is at 20C(68F) - then suddenly we have 35C(95F) in the shade outside. It takes about a week for the floors to heat up). This seems to support the idea the dew point is usually well below 20C.

The choice isn't so much a high wall unit vs hydronic. It is hydronic or nothing. I explain more about why below.


This is every room, right? Also, not every room has space to mount a wall unit on an external wall where an outdoor unit could sit. So we're talking about many sections of horizontal piping inside and outside.

The main structure is a ceramic cavity block called porotherm (it is impossible to carve, it shatters when hit sufficiently hard to break it, it has to be cut with diamond tools to groove it). Inside there is about an inch of "traditional plaster". This is a sand based plaster that is very brittle. If I started grooving porotherm under probably 2~3 inches above and below would fall off.
Outside there is graphite styrofoam 10in of it (glued with a half inch cavity between it and porotherm). On the outside of the styrofoam there is a glass fiber mesh in about half inch of a kind of plaster/glue and on top of tgat there is finally exterior (textured) plaster.

Interior walls are either same material as outside (load bearing) or 5in porous concrete (with same traditional plaster).

Also, where there is no plaster (in the staircase/corridor) there is stone panels on the walls.

So, just punching to the outside is definitely possible, but in many places 2-3m of horizontal section would be needed and you can't hang an outdoor unit on styrofoam so each outdoor unit would need to be at ground level adding a vertical section too. Just thinking about all this work,and how much plastering, grooving it needs (and will still probably not look very good outside and require substantial furniture changes inside). It makes me think the heat is not that bad after all

So in anticipation of problems I started this thread. Condensation is definitely going to be a concern, but I hope it will only limit the usefulness of the system somewhat. Not make it useless.


I do have drainage access in the attic, this would help at least on the upper level of the house.


The key question is, is there too much? I'll definitely not let it get moldy. If I see any condensation ill have to raise the temperature.

Wow, I was going to say that a mini split is much better, but after reading your construction details, I’m not so sure. Is there anyway to use a window air conditioner? Some of the U-shaped window units are very similar to mini splits. Is there anyway to have a central unit with ducting inside? If the house isn’t very big, could you use fans to circulate the air around inside if you had a way of dehumidifying or cooling the air in one room?

 

[Luk88]

Wow, I was going to say that a mini split is much better, but after reading your construction details, I’m not so sure. Is there anyway to use a window air conditioner?

That could be an option for the office. If I just wanted to cool that one room. It is not straightforward as there is only a sloping roof window and a balcony door, but it could probably be done.

If this "hydronic" cooling doesn't work at all that's what I'll do.

For the rest of the house(especially the main bedroom) ... If the unit was removable and I could put it in place for the summer, yes. Otherwise I think I'd rather not install windows units.

Some of the U-shaped window units are very similar to mini splits.

Yes, they look quite mobile.

Is there anyway to have a central unit with ducting inside?

Not really (without substantially tearing up interior walls)

If the house isn’t very big, could you use fans to circulate the air around inside if you had a way of dehumidifying or cooling the air in one room?

If I just leave doors open that is enough to circulate the air within the floor.

Most homes in this area don't have any cooling capability. When I was building my house 8 years ago I didn't really think about cooling. Even now most of my family thinks it's a folly of sorts "it's only ever hot for few weeks a time" etc.

 

[Zwy]

No, not a desert. When I lived in the UK, there there were few very hot summers, but it was always hot and humid - to the point my bamboo window shades were getting moldy with no aircon. Here (in the part of Poland I'm in) it seems it is either cold and wet or hot and dry - still not desert dry.

I have this condensation problem in my basement which has walls at ~2C-5C(35-40F).

I though maybe you did not have a basement, this does change things. I would install a heat pump water heater (HPWH abbreviated) in the basement. This will pull heat from the basement and also act like a dehumidifier reducing the moisture in the basement air.

HPWH can also be ducted, you could add a second unit in series or parallel. Even more if you choose. The ducts can run to the rooms you mainly spend time in. This will pull heat and humidity from that room and return cooler air. Or, you can pull warm humid air from one part of the house thru a duct and return it in another room.

Removing humidity is probably what you need most.

Condensation may well happen, but I hope it will be rare and it will still mean the system is usable (let's say I can increase the temp from 20C (68F) to 24C (75F) - it is still a lot better than 30C(86F indoors). On the other hand I never had condensation in my house even when a heatwave hits while the house is relatively cold (let's say the house is at 20C(68F) - then suddenly we have 35C(95F) in the shade outside. It takes about a week for the floors to heat up). This seems to support the idea the dew point is usually well below 20C.

The problem is as air heats up, the humidity will also rise. Even if the air is cooler, that humidity is still there. It will condense on any surface below the dewpoint temp.

The choice isn't so much a high wall unit vs hydronic. It is hydronic or nothing. I explain more about why below.
This is every room, right?

In my house, I cooled the entire lower floor last year with one 12K mini split in the living room and one 12K window air in the kitchen. For the bedroom I just had a fan that circulated air from the living room to the bedroom. The main cooling was done with the mini split, the window air was only turned on if my wife was baking or cooking and the heat from the stove would heat up the room. We also had a fan circulate air from living room to the kitchen.

For years all we used mainly was the window air. I did add another 18K mini split this spring in the kitchen for more heating and cooling capacity and will no longer use the window air.

It is more about reducing humidity than cooling.

Also, not every room has space to mount a wall unit on an external wall where an outdoor unit could sit. So we're talking about many sections of horizontal piping inside and outside.

I put all my mini split condensing units on cement pads with a stand. Stand is to get the unit off the ground due to snow. Wall mounts aren't my thing on my house, my shop might be a different matter. I didn't want any transfer of sound or vibration thru the wall. I had read countless stories of people who had a wall mount and in the end wished they had a ground mount.

The main structure is a ceramic cavity block called porotherm (it is impossible to carve, it shatters when hit sufficiently hard to break it, it has to be cut with diamond tools to groove it). Inside there is about an inch of "traditional plaster". This is a sand based plaster that is very brittle. If I started grooving porotherm under probably 2~3 inches above and below would fall off.
Outside there is graphite styrofoam 10in of it (glued with a half inch cavity between it and porotherm). On the outside of the styrofoam there is a glass fiber mesh in about half inch of a kind of plaster/glue and on top of tgat there is finally exterior (textured) plaster.

Interior walls are either same material as outside (load bearing) or 5in porous concrete (with same traditional plaster).

Also, where there is no plaster (in the staircase/corridor) there is stone panels on the walls.

So, just punching to the outside is definitely possible, but in many places 2-3m of horizontal section would be needed and you can't hang an outdoor unit on styrofoam so each outdoor unit would need to be at ground level adding a vertical section too. Just thinking about all this work,and how much plastering, grooving it needs (and will still probably not look very good outside and require substantial furniture changes inside). It makes me think the heat is not that bad after all

You have a ceiling and a basement. Lines can go vertically up or horizontal.

So in anticipation of problems I started this thread. Condensation is definitely going to be a concern, but I hope it will only limit the usefulness of the system somewhat. Not make it useless.


I do have drainage access in the attic, this would help at least on the upper level of the house.


The key question is, is there too much? I'll definitely not let it get moldy. If I see any condensation ill have to raise the temperature.

I would start with at least 2 HPWH first. You could use, for example, a pair of 40 gallon, one for control of humidity in the basement and one for the house interior.

 

[wpns]

Another vote for humidity control, sounds like you have a lot of thermal mass and decent insulation. In my uninsulated concrete house the ‘dry’ mode on my Mitsubishi mini-splits makes for the most comfortable environment.

 

[Tulex]

The only people pushing/supporting underfloor cooling are the people who sell/install it. In reality, it just doesn't work well.
When I installed my first radiant heat system over 10 years ago, I read all the forums for radiant heat. Across the board, people who did it were disappointed. Not only is it uncomfortable due to that laws of physics, many people had issues with condensation.

 

[upnorthandpersonal]

So, I have underfloor heating in winter which I use with a heat-pump (a monoblock) in summer for cooling. This works wonderfully where I am in my climate, where we maybe have a week (two at most) of cooling needs per year with temperatures at most reaching 30C for a few days max. The only thing you need to do is make sure you stay under the dew point, but this is not difficult to do really. You do need proper ventilation as well (HRV/ERV).

 

[wpns]

So, I have underfloor heating in winter which I use with a heat-pump (a monoblock) in summer for cooling. This works wonderfully where I am in my climate, where we maybe have a week (two at most) of cooling needs per year with temperatures at most reaching 30C for a few days max. The only thing you need to do is make sure you stay under the dew point, but this is not difficult to do really.

I would think you would need fans of some kind to move the air around and get the cool up off of the floor, and you wouldn’t want rugs for insulation, but it should be doable? My situation is very different, but I’m not surprised to learn that humidity control is the biggest issue.

 

[upnorthandpersonal]

I would think you would need fans of some kind to move the air around and get the cool up off of the floor, and you wouldn’t want rugs for insulation, but it should be doable? My situation is very different, but I’m not surprised to learn that humidity control is the biggest issue.

I just edited that in to my comment. You need an ERV/HRV system... But remember that it's not just the floor getting cold (just like low temp radiant floor heating is not about the floor getting warm). The floor also acts as a sink for IR radiation that would otherwise add heat to the room.

 

[wpns]

I just edited that in to my comment. You need an ERV/HRV system...

Yeah, but another hole in the wall for the OP, and that sounds like a nightmare in his instance.

 

[upnorthandpersonal]

Yeah, but another hole in the wall for the OP, and that sounds like a nightmare in his instance.

Yeah, a house needs to be designed for this from the start. HRV has been standard here in Finland for decades, so I tend to forget that this is not the case in other places...

 

[Luk88]

I though maybe you did not have a basement, this does change things.

I should've said cellar. This "basement" is under another building. A workshop of sorts. My hause has no cellar.

I would install a heat pump water heater (HPWH abbreviated) in the basement. This will pull heat from the basement and also act like a dehumidifier reducing the moisture in the basement air.

HPWH can also be ducted, you could add a second unit in series or parallel. Even more if you choose. The ducts can run to the rooms you mainly spend time in. This will pull heat and humidity from that room and return cooler air. Or, you can pull warm humid air from one part of the house thru a duct and return it in another room.

Removing humidity is probably what you need most.


The problem is as air heats up, the humidity will also rise. Even if the air is cooler, that humidity is still there. It will condense on any surface below the dewpoint temp.



In my house, I cooled the entire lower floor last year with one 12K mini split in the living room and one 12K window air in the kitchen. For the bedroom I just had a fan that circulated air from the living room to the bedroom. The main cooling was done with the mini split, the window air was only turned on if my wife was baking or cooking and the heat from the stove would heat up the room. We also had a fan circulate air from living room to the kitchen.

For years all we used mainly was the window air. I did add another 18K mini split this spring in the kitchen for more heating and cooling capacity and will no longer use the window air.

It is more about reducing humidity than cooling.


I put all my mini split condensing units on cement pads with a stand. Stand is to get the unit off the ground due to snow. Wall mounts aren't my thing on my house, my shop might be a different matter. I didn't want any transfer of sound or vibration thru the wall. I had read countless stories of people who had a wall mount and in the end wished they had a ground mount.


You have a ceiling and a basement. Lines can go vertically up or horizontal.

Sorry for confusion. No basement under the house.

I would start with at least 2 HPWH first. You could use, for example, a pair of 40 gallon, one for control of humidity in the basement and one for the house interior.

2hp is about 1.5kW and we're talking before cop (heat pumps are sized here in kw of heat output rather than electric input). I think thus is pretty much what I'm going for. That 8kW unit has an compressor somewhere in the region of 1500W if I remember correctly.

 

[upnorthandpersonal]

For reference, this one is mine:

PowerWorld PW030-DKZLRS-B/S EasyPlus EVi Air Heat-pump Cooling R32 8.40kW 230V/1Ph/50Hz/60Hz

PowerWorld PW030-DKZLRS-B/S EasyPlus EVi Air Heat-pump Cooling R32 8.40kW 230V/1Ph/50Hz/60Hz for DHW, under floor and many more applications The new

www.orionairsales.co.uk

Takes care of 120m^2 and all domestic hot water in spring/autumn, so your 8kW idea for your unit sounds ok, you can probably go smaller.

 

[Luk88]

The only people pushing/supporting underfloor cooling are the people who sell/install it. In reality, it just doesn't work well.
When I installed my first radiant heat system over 10 years ago, I read all the forums for radiant heat. Across the board, people who did it were disappointed. Not only is it uncomfortable due to that laws of physics, many people had issues with condensation.

I beg to differ regarding heating. 6 years of comfortable and cheap winters living in my house with underfloor heating says it works for heating. Perhaps you meant it about combined heating/cooling. I'm going to find out about cooling soon for myself...

Also, good insulation and lots of mass matters a lot. I lived in houses heated with everything. From an old fire brick stove built in a middle of a house which spans multiple rooms(see one of these "how we live in siberia youtube videos" - To see one, hot water radiators powered by district hot water, fully central air system in modern buildings, underfloor electric, and now underfloor low temp water.

From the living comfort point of view I put underfloor heating even above central air. Hot water radiators(combined with bad insulation so they always run on full blast - bonus points if they are also broken so you can't switch them off) are horrible because they dry the air. I had lots of sinus problems in my youth thanks to these.

I'd be interested (if it was meant in the context of heating too) where underfloor heating doesn't work?

I would think you would need fans of some kind to move the air around and get the cool up off of the floor, and you wouldn’t want rugs for insulation, but it should be doable? My situation is very different, but I’m not surprised to learn that humidity control is the biggest issue.

There are no rugs in my home. Just stone and tile floors. (makes vacuuming so much easier).

I have manual valves for every room (and for half of a room in the master bedroom and a living room) so I could make certain parts of the house cool slower And maybe put a portable dehumidifier in the office where I'll really need the cooling power

I just edited that in to my comment. You need an ERV/HRV system... But remember that it's not just the floor getting cold (just like low temp radiant floor heating is not about the floor getting warm). The floor also acts as a sink for IR radiation that would otherwise add heat to the room.

That would require air ducting to send the air around the house I guess. If I could install air ducting I would use what they call hydroconverter - it uses a heat exchanger to cool air using the cool water from the heat pump. Or maybe even a centrally installed air-air instead of an air-water unit.

Yeah, a house needs to be designed for this from the start. HRV has been standard here in Finland for decades, so I tend to forget that this is not the case in other places...

Definitely. When I was in design stages of building my house HRV was gaining in popularity, but it was very expensive. Solar was also a lot more expensive. Cheap solar and cheap batteries are a huge enabling factor to start using electricity for heating/cooling.

I chose a lot of stuff to improve energy use(building materials, triple glazing, insulation etc) , but HRV at the time would double the house cost (seriously). So it wasn't done. If I was building now... I'd definitely do it.

My sister is building her house now, but she is as broke during it as I was... So probably she too will not install central air. Perhaps I can convince her to at least put the ducting in, but she too is using porotherm. That material is great for many things, but putting large ducts in walls is not one of them.

For reference, this one is mine:

PowerWorld PW030-DKZLRS-B/S EasyPlus EVi Air Heat-pump Cooling R32 8.40kW 230V/1Ph/50Hz/60Hz

PowerWorld PW030-DKZLRS-B/S EasyPlus EVi Air Heat-pump Cooling R32 8.40kW 230V/1Ph/50Hz/60Hz for DHW, under floor and many more applications The new

www.orionairsales.co.uk

Takes care of 120m^2 and all domestic hot water in spring/autumn, so your 8kW idea for your unit sounds ok, you can probably go smaller.

Thanks. The specs look very similar. 120m2 is substantially larger than my house.

There is a 6kW model I could've chosen, but it cost slightly more than the 8kW unit and I read somewhere these units are more efficient at heating than cooling. So I chose 8kw thinking better to err on slightly too large than too small.

Is there any potential downside to oversizing the heat pump by ~10-20%?

I initially intend to only use it for cooling and maybe some heating when we have good light and it is still fairly cold in the spring. I haven't got the space for a large hot water tank to heat domestic water with it (unless I got rid of the pellet burner, but I'm planning to keep it at least for now).

My pv calculator says there is no way I can meet my electricity demand and heat the house with a heat pump in winter (currently 2.4kW,adding 14kW) and who knows how much grid electricity will cost in future. So that's the reason for leaving the pellet burner in.