Heating a outside guest room

[theloneboarder]

Hello all,
I’m currently converting a brick stable attached to my house into a guestroom with ensuite.
100mm insulation under the osb floor.
75mm insulation on the walls, over boarded with 25mm insulated plasterboard.
Wool insulation in the vaulted roof, and then probably 25mm Insulated plasterboard over that.
Basically I’m trying to turn this stable into an airtight cocoon.
I am reasonably confident this room will be pretty well insulated but, what would be the best way to heat it?
I was thinking of electric underfloor heating throughout, as it would only need to be turned on when a guest comes to stay. By the way, I imagine it’ll only get used once a month for a couple of nights.
A wet underfloor heating system isn’t an option.
A2A heat pump isn’t something I really want either, mainly due to aesthetics of where the pump would be placed.
I think the bathroom will be tiled and laminate or engineered wood for the main floor. Bathroom is about 4 m² and bedroom is 22 m².
Any advice from anyone please ?
Thanks

 

[Ivor Windybottom]

For that sort of usage just any electric heater. Just get literally anything - radiators, convectors, an electric fire. It doesn't matter, they all cost the same to run so it's just a matter of cosmetics. A £500 heater will cost the same to run as a £20 one.

Underfloor heating wouldn't be that good for occasional use, as you'd never build up the thermal mass. It would be cold when you wanted it warm, then remain warm after you'd done with it.

You could pay more for storage heaters or a heat pump and use less energy, but from it getting used a couple of times a month you'd never recoup your investment in energy savings.

Obviously the supply cable needs to be sufficient.

 

[matlob]

I heated a timber garden office with just a portable oil filled radiator. It was nowhere near as well insulated as your specs. Takes a while to warm the space but if you know someone is coming you can heat it in advance

I would use the pir in the ceiling too if possible

 

[stem]

Some electric underfloor floor heating is designed only to warm the floor surface so that it's not cold to walk on. It's not intended to physically heat the room. So obviously, any UFH would have to provide sufficient heat for the size of the room. Off the top of my head, I would estimate that the main room will require 2 to 3 kW, and the bathroom 0.5 to 1 kW. This is just my guess; so I suggest that you use an online calculator to check. Once you know how much heat you need, you can find out if the electric UFH you are considering would provide enough. 150 W per m² would equate to 3.3 kW for your 22 m² room.

However, because of its low surface temperature, even wet UFH can take several hours to warm a room from scratch, and in cold weather many users find that it has to be left on permanently, especially if a good portion of the floor area is covered with furniture or rugs.

It's vital that the floor below the UFH is well insulated too. Otherwise much of the heat will be absorbed by the ground and lost.

I have a similar situation with a garden room and I use a 3 kW wall mounted convector heater with a built in fan heater. With both the convector and fan on it heats the room very quickly. Minutes rather than hours. Then once it's warm I turn the fan part off and just leave the convector on to maintain the temperature using its inbuilt thermostat.

It's a shame you can't consider a split unit ASHP, they are more expensive, but they provide a fast warm up and can have efficiencies of 300% meaning that you would get 3 kW of heat from 1 kW of electricity. With the added advantage of A/C cooling in the summer. Then an electric towel rail and perhaps UFH mat for the bathroom.

 

[theloneboarder]

Some electric underfloor floor heating is designed only to warm the floor surface so that it's not cold to walk on. It's not intended to physically heat the room. So obviously, any UFH would have to provide sufficient heat for the size of the room. Off the top of my head, I would estimate that the main room will require 2 to 3 kW, and the bathroom 0.5 to 1 kW. This is just my guess; so I suggest that you use an online calculator to check. Once you know how much heat you need, you can find out if the electric UFH you are considering would provide enough. 150 W per m² would equate to 3.3 kW for your 22 m² room.

However, because of its low surface temperature, even wet UFH can take several hours to warm a room from scratch, and in cold weather many users find that it has to be left on permanently, especially if a good portion of the floor area is covered with furniture or rugs.

It's vital that the floor below the UFH is well insulated too. Otherwise much of the heat will be absorbed by the ground and lost.

I have a similar situation with a garden room and I use a 3 kW wall mounted convector heater with a built in fan heater. With both the convector and fan on it heats the room very quickly. Minutes rather than hours. Then once it's warm I turn the fan part off and just leave the convector on to maintain the temperature using its inbuilt thermostat.

It's a shame you can't consider a split unit ASHP, they are more expensive, but they provide a fast warm up and can have efficiencies of 300% meaning that you would get 3 kW of heat from 1 kW of electricity. With the added advantage of A/C cooling in the summer. Then an electric towel rail and perhaps UFH mat for the bathroom.

Stem,
This is giving me food for thought. The reason I didn’t want to mini split was because I assumed the external unit would have to be cited close to the internal unit. This would mean we having the external unit in a courtyard garden which would look a bit ugly.

Having briefly read up on them now, it would seem that the connecting line between the two units can be quite some distance. This means I could potentially place the external unit somewhere else out of sight.

A few more of my brain cells and then started talking to each other because, I am also building a midlife-crisis gym on the other side of the guest room. I’m now thinking I could potentially get a mini split system that comes with two internal units. One for the guestroom and one for the gym.

Regarding the costs, I was thinking that an electric UFH system was probably going cost over £1000 by the time I add all the other flooring components etc and this is probably not going be too far off the cost of a split system with two internal units.

From what I’m saying do you think a twin mini split would be more suitable for both rooms? The external unit would probably be cited some 10 -15 m away from the internal units with a vertical drop of about 2m.
Thanks for your help

 

[big-all]

Hello all,
I’m currently converting a brick stable attached to my house into a guestroom with ensuite.
100mm insulation under the osb floor.
75mm insulation on the walls, over boarded with 25mm insulated plasterboard.
Wool insulation in the vaulted roof, and then probably 25mm Insulated plasterboard over that.
Basically I’m trying to turn this stable into an airtight cocoon.
I am reasonably confident this room will be pretty well insulated but, what would be the best way to heat it?
I was thinking of electric underfloor heating throughout, as it would only need to be turned on when a guest comes to stay. By the way, I imagine it’ll only get used once a month for a couple of nights.
A wet underfloor heating system isn’t an option.
A2A heat pump isn’t something I really want either, mainly due to aesthetics of where the pump would be placed.
I think the bathroom will be tiled and laminate or engineered wood for the main floor. Bathroom is about 4 m² and bedroom is 22 m².
Any advice from anyone please ?
Thanks

no expert at all

insulation seems a bit thin for an" air tight cocoon" but just my guess
also heat require depends on volume a barn suggests high roofs ??

 

[George_engineer]

Stem,
This is giving me food for thought. The reason I didn’t want to mini split was because I assumed the external unit would have to be cited close to the internal unit. This would mean we having the external unit in a courtyard garden which would look a bit ugly.

Having briefly read up on them now, it would seem that the connecting line between the two units can be quite some distance. This means I could potentially place the external unit somewhere else out of sight.

A few more of my brain cells and then started talking to each other because, I am also building a midlife-crisis gym on the other side of the guest room. I’m now thinking I could potentially get a mini split system that comes with two internal units. One for the guestroom and one for the gym.

Regarding the costs, I was thinking that an electric UFH system was probably going cost over £1000 by the time I add all the other flooring components etc and this is probably not going be too far off the cost of a split system with two internal units.

From what I’m saying do you think a twin mini split would be more suitable for both rooms? The external unit would probably be cited some 10 -15 m away from the internal units with a vertical drop of about 2m.
Thanks for your help

10 to 15m might be pushing it but talk to some installers. There are some all in one system but they do take a small chunk of indoor space

I'm currently converting an outbuilding to an office and using a heat pump. The Air conditioning makes it worthwhile alone.

 

[theloneboarder]

no expert at all

insulation seems a bit thin for an" air tight cocoon" but just my guess
also heat require depends on volume a barn suggests high roofs ??

Ridge is only 3.8m as it's a stable, not a barn. Insulation should be adequate but by stating "airtight" I mean by making sure there are no gaps for draughts etc.

 

[stem]

From what I’m saying do you think a twin mini split would be more suitable for both rooms? The external unit would probably be cited some 10 -15 m away from the internal units with a vertical drop of about 2m.

I would have thought so, but as @George_engineer suggests have a chat with the pro's. My limited experience is with a larger A/C installation not split units.

 

[Rodders53]

Around double that £1k for a twin split of decent brand with longer runs of pipework; plus installation by a F-gas certified bod.
https://www.saturnsales.co.uk/Mitsubishi-Multi-Heat-Pumps-Air-Conditioning.html is an example retailer with a variety of brands to look at.