Heating and Water for Outbuilding

[h901]

Hi

I've got a large outbuilding in my garden and it has its own bathroom. I'm wanting to put hot water and heating in the outbuilding but not sure what the best approach would be. I was thinking of an electric water heater/electric shower but most of the ones I've seen have such slow flow rates. Ideally I'd like water flow like I have in the house (from the boiler) and heating from a radiator, but I think this would be a big job.

Can anybody suggest some ideas?

Thanks

 

[muggles]

Without knowing what setup you have in your main house, it's impossible to suggest what kind of system might match its performance for the outbuilding. More information please...

What is your mains flow rate like in your outbuilding? Are you on gas/oil/LPG in the house?

 

[h901]

Without knowing what setup you have in your main house, it's impossible to suggest what kind of system might match its performance for the outbuilding. More information please...

What is your mains flow rate like in your outbuilding? Are you on gas/oil/LPG in the house?

I've got a Ideal Combi 30 boiler in the house. Thanks

 

[Doggit]

How big is the outbuilding, and how far away is it from the main building.

 

[h901]

How big is the outbuilding, and how far away is it from the main building.

It's approx 4.5m x 3.5m and around 10 metres away from the house.

In terms of heating, I like the idea of underfloor heating so that could be an option.

 

[muggles]

A single-zone retrofit UFH kit is going to set you back over £1k just to buy, then there are installation costs...

There's no theoretical reason why you shouldn't have a second gas boiler in your outbuilding, but you'd need to find a route to run the gas pipe. This can be underground if required. You also can't have a total load on your existing gas meter of more than 70kW, so two 30kW combi boilers and a hob take you close to the limit, if you've got a fire as well then something is going to have to go, or you go down to a 24kW combi which will give you slightly less hot water performance but still adequate for a shower.

 

[h901]

A single-zone retrofit UFH kit is going to set you back over £1k just to buy, then there are installation costs...

There's no theoretical reason why you shouldn't have a second gas boiler in your outbuilding, but you'd need to find a route to run the gas pipe. This can be underground if required. You also can't have a total load on your existing gas meter of more than 70kW, so two 30kW combi boilers and a hob take you close to the limit, if you've got a fire as well then something is going to have to go, or you go down to a 24kW combi which will give you slightly less hot water performance but still adequate for a shower.

Thanks for your reply

What would you recommend in this situation especially in terms of hot water? The outbuilding is only one room and a bathroom and in the house I have a gas hob, gas oven and 30kW boiler.

 

[muggles]

I still don't know your mains cold water flow rate so it's still a little hard to spec, but 28kW should squeeze under the 70kW limit. I'm assuming your hob is 8kW, and your oven is 3kW. 30+28+8+3=69kW. A combi is going to be horribly inefficient trying to just heat one room, and the only one out there with any hope of doing it successfully is the Vokera Unica i28, but even that will be over-powered and suffer from continual cycling, shortening its life and costing a lot to run in the process.

Personally I'd go for a gas-fired water heater such as the Main Multipoint or the Vokera Aquanova, and an electric radiator. It'll be cheaper both initially, and in the long run.

 

[Doggit]

You could attach the outbuilding to your existing central heating system using something like Microflex DN20. This could also be used for the shower, but you're wasting a lot of gas and water waiting for the hot water to get through. A 9Kw electric shower will give you a good flow rate, but what are the electrics like both to the outbuilding, and in it as well.

 

[h901]

Thanks guys

I think I'm going to go with underfloor heating instead of a radiator.

I'm not sure what my mains cold water flow rate is, but there is a decent amount of pressure from the shower, would a 9Kw electric shower give the equivalent of shower powered by the combi boiler (let's say I have average flow rate if there is such a thing) sorry for being so vague.

 

[Doggit]

Put a bucket under the tap, run the water for 30 seconds, and check how much has come out, and then double it, and that'll give you the flow rate per minute.

A 24Kw boiler will handle 9 litres per minute, and a 28Kw will do 11.

Depending on how the outbuilding is constructed, a radiator is dead easy to install, but underfloor heating may require a fairly massive rework. You need 100mm pir insulation underneath it, then spreader plates, and then floorboards on top. You need 150mm in total, either below your existing floor, or to raise it up by that amount. As underfloor heating runs at a lower temperature to radiators, you also need a mixer valve to add cooler water to the existing central heating water. In addition, because underfloor heating takes longer to bring a room up to the required temperature, the boiler would need to come on earlier, and just feed that section, before coming online for the main house.

 

[h901]

Put a bucket under the tap, run the water for 30 seconds, and check how much has come out, and then double it, and that'll give you the flow rate per minute.

A 24Kw boiler will handle 9 litres per minute, and a 28Kw will do 11.

Depending on how the outbuilding is constructed, a radiator is dead easy to install, but underfloor heating may require a fairly massive rework. You need 100mm pir insulation underneath it, then spreader plates, and then floorboards on top. You need 150mm in total, either below your existing floor, or to raise it up by that amount. As underfloor heating runs at a lower temperature to radiators, you also need a mixer valve to add cooler water to the existing central heating water. In addition, because underfloor heating takes longer to bring a room up to the required temperature, the boiler would need to come on earlier, and just feed that section, before coming online for the main house.

Oh ok, I'll check the flow rate in the morning.

I'm planning on having some work done on the outbuilding soon (new roof and changing the position of the bathroom) so could get the underfloor heating done then.

Do you not recommend electric underfloor heating?

 

[Doggit]

Not unless you've got very deep pockets. Electric heating costs about 3 times as much as gas does, but it would be cheaper to install than an addition to your main house system. There a lot of new hybrid heaters coming on to the market that a cross between a storage heater and a panel heater. And they can have pictures on them to make them works of art.

 

[Madrab]

would a 9Kw electric shower give the equivalent of shower powered by the combi boile

If your combi is giving full rate HW then no, a 9kw shower will not give you the same intensity of a shower as your combi would.

What type of occupancy is the outbuilding going to be? Is it to be a continuous occupancy or is it going to be sporadic? If the latter then point of use heating and hot water is going to be the most efficient. If it's to be a normal day to day occupancy then it's going to take a more permanent solution

 

[h901]

would a 9Kw electric shower give the equivalent of shower powered by the combi boile

If your combi is giving full rate HW then no, a 9kw shower will not give you the same intensity of a shower as your combi would.

What type of occupancy is the outbuilding going to be? Is it to be a continuous occupancy or is it going to be sporadic? If the latter then point of use heating and hot water is going to be the most efficient. If it's to be a normal day to day occupancy then it's going to take a more permanent solution

It's going to be normal day to day use