Hello all We're in the process of renovating an outbuilding and are looking at various heating options.The room we need to heat is 5mx7m with a pitched roof which is 4m high at its highest point. We have water and electric in the building but no access to gas or an oil tank. The room is insulated and drylined. We're looking for some ideas for a primary heating source for this - and are open to any sensible suggestions. As we have capacity in our house central heating system it has been suggested we drill holes in one of the house exterior walls and attach pipes between the house and the outbuilding at approx 10 feet off the ground. Anyone any thoughts on this - is it a viable option? What would we need to lag the pipes with? Does anyone have any better suggestions?
The first thing is to get the insulation sorted out. These days the requirements are strict and you will need building regulations approval for it. This should include details of the heating arrangements. Your local building control department should be able to give you some pointers. Don't expect it to be cheap though.
Yes, bury the pipes underground. Use MDPE, well lagged buried below the local height required for frost protection. Your local water company can advise on recommended burial depths for your local area.
The new system connect into your central heating using a plate heat exchanger on its own zone. This separates the outbuilding primary circuit from your main one, making servicing easier and ensuring that the house system is not compromised if there is a problem in the outbuilding or underground pipework.
There will need to be an signal connection between the outbuilding and the house so that when the programmable thermostat calls for heat, it can open the heat exchanger zone valve and fire up the boiler/house pump. The outbuilding pump can be either in the house or outbuilding.
I have done an exercise almost identical to this with a building (large garage to be precise) used as a workshop. It's a little larger than what you describe but of the same order.
Its a single skin brick construction with wooden doors at one end and prior to doing anything would require 12kW in fan heaters to bring it up to house temperatures of 18 degrees plus. In practice I didn't do that and used 6kW of fan heater capacity which was always inadequate, took a long time to warm up and was expensive to run. It's easy to work out what.
My first task was to insulate it, in effect to about the equivalent of the current requirements for a house - at least in terms of heat loss through walls and roof. This was done using sheets of Celotex insulation because it has a very low U value (heat loss factor) for a given thickness. I used timber framing and a ply clad so that I can fix things easily to the walls. I insulated the doors similarly and draught proofed with sealing strips.
I had calculated what the heat losses would be after doing this and it came down to around 3kW to maintain the desired 18-21 degrees with -1 to -3 outside. Following the insulation work, I did some measurements using one fan heater, and the results were close to what was predicted.
So this is really the first step. Take a look at the insulation of the building and calculate what you will need in terms of heat. The radiator manufacturers have claculator programs to help with this but you need to know the nature of the insulation and the rest of the construction to be able to plug in the correct heat loss U values. Myson and Barlo both have reasonably good programs, although Myson's is not on their site last time I looked. If you want to drop me an email I can send it to you.
If you are using the building as habitable space, it is a Building Regulations requirement to insulate it to certain defined levels. You can find details of this in Approved Documents to the Building Regulations on
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Look at Part L1.
I still didn't want to use electricity for heating because I wanted to maintain a minimum temperature of 10 degrees to keep materials and tools from becoming affected by damp in the air.
I found references to how to deal with the case of having a boiler in an outbuilding on the web site of the Northern Ireland Building Regulations web site. However it no longer seems to be there. I can send you a copy if you like.
Essentially, the idea is to use PVCu pipe (e.g. soil pipe(s) of 100 or
150mm diameter) buried in the ground and to run the heating flow and return carrier pipes in that, insulating them with fairly substantial pipe insulation.
First one would have to check pipe run distances and diameters. For me, 22mm pipes were enough, but the garage is only a few metres from the house. If you have a long run, you may need larger diameter pipes. For 22mm pipe, the recommendation was to use 22mm insulation such as Armaflex. You can fit two of these in a 150mm duct. The recommendation for the duct is to bury it at a depth of 150 to 500mm and surrounded in sand or pea gravel. Each end is then brought into its building.
For the carrier pipes themselves, copper could be used, but it is a lot easier to use plastic barrier pipe for the purpose since it can be bent more easily while assembling the duct.
This gets you the basic installation.
Even with the insulation methods described, there would need to be some frost protection to prevent water in the carrier pipes from eventually freezing - i.e. running the pump and the boiler for short periods if temperatures fall
I felt that it was important, considering that this was an outbuilding that *could* be unheated, to have a way to protect the integrity of the house heating system from failure or freezing related to the outbuilding, so I took a different approach.
The circuit for the outbuilding is run completely isolated from the house one by the use of a stainless steel heat exchanger.
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are typically used for thermal stores etc. where it is necessary to transfer a lot of heat quickly between separate bodies of water (in that case heated water in a cylinder to a flow of mains tap water). They cost under £100 and work very efficiently - i.e. for this purpose do not limit the rate of heat transfer between circuits. FOr heating purposes on this scale, it is as though the circuits were really one.
THe technique is also used for heating swimming pools.
The primary (supply side) of the heat exchanger is connected into the indoors heating circuit as though it is a heating zone. Heating water flow to it is controlled by a motorised valve according to Honeywell's S-plan+ scheme.
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valve is controlled by a flow switch (as opposed to a room thermostat) fitted in the *secondary* circuit from the heat exchanger. More of this in a moment.
The secondary circuit is filled and pressurised with a sealed system vessel as though it was a conventional sealed CH system but with the heat exchanger being the heat source (i.e. "boiler"). One could use an open vented arrangement but there is no need.
I fitted the pump and a room thermostat/time controller in the outbuilding. This is a simple arrangement and the pump runs and circulates water in the secondary circuit when heat is needed. The flow switch in the circuit, located near the heat exchanger in the house, operates when secondary water flows, causes the motorised valve feeding the heat exchanger to open and the boiler to fire. The advantage of this approach is that there is totally separate control for the outbuilding without the need to have control wiring back to the house.
I didn't want to mess about with frost thermostats etc., so I used an alternative approach of a corrosion inhibitor with antifreeze (Fernox Alphi-11) in the secondary circuit. THis stuff is relatively expensive which is another reason to have separate circuits. I added sufficient to protect down to -20 degrees which should cover anything in the UK at present.
Finally, I did size the radiators larger than needed to compensate for heat loss. This is because I often like to go and use the workshop in the evening and want it to warm quickly. Therefore there is 9kW of radiator capacity, even though only 3-4 is needed in the steady state.
How does it work? Really rather well and this is the third winter. Not an expensive solution in terms of capital cost either. THe fiddliest bit was threading the insulated pipes through the duct work on a cold day. Plastic pipe is not as flexible when cold as one might like.
Putting a humidistatic dehumidifier in instead of always heating would save you a nice sum. Even if you add a 3kW electric fan to help bring it upto temp when you go there in the evening.
I don't really want the wide temperature swings either. There is in any case a dehumidifier which is used when needed.
Considering the average temperatures through the year and amount of the time that it is below 10 degrees inside, I calculated it to be about 300W of heating on a continuous basis. At 2p a unit, it's about £50 a year which is fine as far as I'm concerned.
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