Heating and hot water options in an outbuilding

[platforminc]

Hi all.

I am constructing an outbuilding, it has a small toilet and a small shower built in. The dimension is 8m x 3.5m for the entire build, the shower & toilet measures 1m x 3.5m.

As its an outbuilding which will serve as an office and a gym, I am unsure as to what heating/hot water option to go for. At this point underfloor heating is out of the question as I want vinyl tiles or laminate flooring, the flooring has been raised now and underfloor heating is not possible.


The main house is being refurbished, the proposed heating system is an unvented cylinder with underfloor heating. The cylinder will be about 17m away from the outbuilding. The gas meter is about 23m away from the outbuilding. The water pressure is pretty good, although it will be upgraded to a 25mm blue pipe.

I wanted to know what my options are here.

 

[Gasguru]

Presumably it will be fully insulated and therefore the heatloss would be minimal so for simplicity go all electric....
Do the heat calculations and you might find you only need a kW or so of heat coupled with an unvented cyl for the water to give a good shower.


Getting heated water to outbuildings is an extortionate cost as the insulated pipe and fittings are crazy money.

 

[platforminc]

Thanks for the reply, the outbuilding wall is cavity constructed and fully insulated all the way, the roof loft is also insulated.
For the main outbuilding, I think 2 small electric heaters will do for the simplicity as you said.

For the shower, we have a 15mm feed of cold water going into the shower, what are my options for the shower ? Will an electric shower do ?
The unvented cylinder, is that a direct/indirect and what sort of capacity, does it need to sit on the floor/hung on the wall etc as I need to think about where to site it, if one is going that way.

Thanks in advance.

 

[Elkato531]

I would go all electric as said above. An electric shower is the simplest option. It won't give as a good a shower as you might get from an unvented cylinder but if its only going to be for a quick shower after using the gym it should be adequate. Apart from the shower, hot water use would be minimal and a small 10 or 15litre unvented undersink heater would supply more than enough for a basin and washing up sink.

 

[platforminc]

I was also thinking, could a 24kw boiler not work, I say this because when I start to think about the individual electric stuff I will need to get vs getting a small cheap 24kw boiler, that will have a good shower, radiators attached to it, basin attached to it.

With electric.

I will need.

2 x electric heaters.
1 x electric shower
1 x electric towel heater
1 x basin heater.

Whilst I know the place isnt going to be used that much, but as its still a building site, I really want to think about it, and not have regrets later in future.

The other reason I say so is that, I recovered a lot of radiators from the main house which will now be redundant due to having underfloor heating, so they could be put to use here.

Just a thought.

 

[ianmcd]

Agree electric shower is your cheapest option

 

[Elkato531]

You will need the appliances you listed but each of those will be less than £200, probably closer to £100 each. Versus the cost of boiler and heating pipework installation plus cost of running 20 odd metres of gas underground. If you're planning on falling out with your other half and living in it, I'd go with the boiler. If not, go electric.

 

[Gasguru]

If the insulation and draught proofing is done properly most 24Kw combis will just sit there cycling as their heat output on heating won't go sufficiently low.

An unvented and simple thermostatic bar shower for me.

Also work out the cost of cabling...17plus meters of armoured of sufficient size for a decent electric shower, say 10 or 12 kW (and the rest of the installtion) won't be cheap, whereas a cylinders 3Kw immersion is more manageble.

A 90 litre unvented....

https://www.plumbnation.co.uk/site/discount-direct-stainless-unvented-cylinders/

Or maybe even a 50 litre wall hung cylinder would be sufficient.

 

[platforminc]

Thanks for the reply.
The cabling has already been buried in the ground, I believe its a 16mm armoured but cant remember.
The unvented you talk about, will this work for shower and wash basin, if the water finishes in the tank, does this mean that the shower will suddenly be cold ?

Its a tough one, I know I will not use hte shower that much, my experience of electric shower is poor, the water pressure is just not there (9kw shower).

I am looking at the unvented cylinder option as a dual solutoin option. The 90 litre, will this be wall hung or floor standing ?

Thanks in advance.

If the insulation and draught proofing is done properly most 24Kw combis will just sit there cycling as their heat output on heating won't go sufficiently low.

An unvented and simple thermostatic bar shower for me.

Also work out the cost of cabling...17plus meters of armoured of sufficient size for a decent electric shower, say 10 or 12 kW (and the rest of the installtion) won't be cheap, whereas a cylinders 3Kw immersion is more manageble.

A 90 litre unvented....

https://www.plumbnation.co.uk/site/discount-direct-stainless-unvented-cylinders/

Or maybe even a 50 litre wall hung cylinder would be sufficient.

 

[Gasguru]

16mm armoured should leave you the option of an electric shower (perhaps even a higher kW but calculations are required with the total load known).
Yes the unvented would do all the hot water requirement, and yes if you use up all the water the shower will go cold...the cylinder capacity is sized accordingly and an allowance for heat up time.
However, you will get a vastly superior shower with a cylinder (assuming water pressure/flowrates are adequate) over an electric shower especially in the winter when incoming temperatures are lower.

Work out the shower flowrate required (you can limit it with a flow limiting insert on the shower), lets say 10 litres/min (even 8 litres/min will seem like luxury after most electric showers).
Now assume a worst case of a 70%/30% hot/cold water mix and you have a 7litre/min hot water flowrate requirement so size your cylinder accordingly (ie.how long in the shower).

By comparison a 9kW electric shower will give you around 3.5 litres/min and a 12kW no more than 5 litres/min in the deapths of winter.

90 litres cylinders are floor standing but if you have the height you can always get a blacksmith to knock up a frame or gallows brackets, 50 litre cylinders are wall mounted.
Remember the traditional sized cylinder for your average house is only 120 litres (sure some have much larger cylinders but often it's unecessary).

 

[hard-work]

A number of options:

1. Take an underground gas pipe (yellow plastic) to the outbuilding, fit a small combi with Opentherm, and an Opentherm thermostat. Any burner cycling would be minimal. Modern combis modulate low. The lowest kW may be above the heat demand for the building, but the Opentherm stat will cut the heating out when up to temperature and keep the boiler's burner low. Use a normal shower mixer. Also run 25mm blue plastic water pipe to the building. Avoid cylinders as they take up space.
   
   
2. Go all electric, which will be cheaper to install. Need to size the underground cable properly. Electric UFH can go under laminate flooring - use a Heatmiser thermostat/timer. The shower and sink/basin can be run off one 11kW instant hot water heater hidden away (could be in an outside cupboard accessed only from outside. A number of them on the market with varying prices. The shower mixer, can be a normal shower mixer. Have the shower head a Raindance aerated eco head which gives only 9 litres/minute mixed hot and cold. They add air to the water flow. https://culmstoreseltermltd.co.uk/i...MVM9SvynwW-v1xzkGEwLiR58ioBQ8zRhoC0S0QAvD_BwE You could have instant electric taps and a normal 9kW instant shower. But these tend to look like hideous white boxes in the shower cubicle. They look cheap.

If the building is well insulated - well over the buildings regs levels which is very wise to do. I would be inclined to go for number 2. above, as you will use little electricity anyhow. The money you save in installation buys a lot of electricity. Also, in about 5 years time gas boilers will be outlawed in new builds. So you will be ahead of the game.