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Author Topic: Solar Forum Plumbing FAQ - New members please read this first  (Read 37144 times)
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« on: August 07, 2006, 04:16:00 PM »

Welcome to the Solar Forum Plumbing FAQ

This section of the Solar Forum FAQ covers the Plumbing aspects of a solar installation. It can also be found in the Wiki section of the website at

For the Solar Forum Control and Electrical FAQ please see or on the Wiki at

The FAQ has being split due to maximum post length being reached, thus preventing additions to the information.

The Solar Forum Plumbing FAQ is intended to supplement the FAQ on the Navitron website see  and is based on common questions and discussion threads within the Forum.

There is also plenty of information on the Solar section of the website see  including downloadable files.

Please note: This topic is locked to prevent it becoming an eternal thread, as it is intended to be an FAQ only. It will be updated whenever suitable topics arise.

What size solar panel and cylinder should I fit?
The system can be sized to optimise solar gain during winter, but this would be at the expense of excess heat generation during summer, requiring frequent ‘dumping’ of the excess heat. Conversely, sizing the system specifically for summer solar insolation will limit the temperatures achievable during winter months requiring more input from the boiler..
Therefore some compromise is required in conjunction with an assessment of the domestic water useage and the hot water temperatures required.
The general rule of thumb is to allow 5.5 to 8.5 litres of water per solar tube depending on location and water consumption.

Do I need planning permission?
With government energy policies promoting Renewable Energy, it is becoming increasingly difficult for local Planning Departments to refuse permission for RE sources - especially non-obtrusive ones like solar panels.

New Planning Rules from 6th April 2008 have made it easier to install solar panels without requiring formal planning consent - providing the panel does not impact on others.
It may still be advisable to contact your local Planning Officer before installing the panel, outlining the size and position of the proposed panel on your roof, relative to any public rights of way including roads. (Some Councils may still object if a panel is visible from the Public Highway).
Once you have received a written response stating that Planning Permission is not required, the installation can go ahead with no fear of future reprisals. Any letter must be retained for evidence should the property be sold in the future.

Note though that if you live in a conservation area or own a listed building, you will almost certainly require planning permission that may be more difficult to obtain.

Are Solar panels subject to Building Regulations?
This seems to create a mixed response from Building Control (BC) Departments. As with Planning permission it is wise to write to your BC department and seek confirmation. It is helpful if you tell them the sort of roof construction you have, the type of tiles and whether these are the same type (if you know) as the original construction. For example a roof that originally had slates may be overstressed if these have already been replaced with concrete tiles. A 20 tube system will add around 50kg to the roof. This is of course is spread over the width of the frame and should not present a problem in most circumstances.

The installation also needs to conform to Part L and Part P of the Building Regulations. If you are installing or replacing an unvented (pressurised) cylinder this must be carried out by a Regulation G3 certified plumber who should provide a Commissioning Certificate.

Some BC Departments have said that they are not interested; that may be because the quantity of installations are currently low and they themselves are not familiar with solar systems. As the number of installations increase then BC Depts will doubtless take more interest. The best approach is to ask, and get written confirmation of any statement that permission is not required.
Unfortunately regulations are continually being updated - further limiting what the DIY installer can (legally) do. In the medium to long term, this may well work against the interests of both the industry and the government's desire to encourage energy saving...

I have a non-standard cylinder requirement
Whilst ‘standard’ sized cylinders may be available from Navitron stock, they can also be manufactured to customer specification as regards number and type of coils, connection positions, compression union sizes etc. Please fax Navitron a drawing showing the required boss positions, coils etc for a custom quote.

What size pipe should I use for the solar loop?
For most domestic installations, 10mm copper pipe has been found to allow suitable flow rates and seriously reduces pipework thermal losses.  Alternatively 15mm can be used. The manifold connections are  22mm though, so 22mm compression elbows can be fitted on the manifold stub pipes and reducing sets or adaptors used to take chosen copper through the roof tiles.
Keep all solar pipe runs as short and direct as possible. The use of bends rather than elbow fittings improves flow.

What is in the big red Expansion Vessel for and why do I need it?
As the solar panel is often the highest point in the system, the solar installation has to run as a sealed system. When water is heated, it expands. In a plain sealed loop of pipework, there would be nowhere for the expanded water volume to go. The system pressure would rapidly increase until something bursts!

The Expansion Vessel is a form of pressure vessel containing a rubberised bladder. On one side is a gas (often nitrogen) pre-pressurised to 1.0 or 1.5 bar. The solar water loop is connected by a pipe to the other side of the bladder. As the pressure in the solar system increases, so the bladder compresses against the gas thus giving the increased water volume 'somewhere to go'.

The added advantage of a pressurised system is that the boiling point of the solar loop is raised above 100 deg C - useful in the event of something going wrong.

The Navitron kit Expansion Vessel has a 12 litre capacity which is ample for domestic solar installations. An 8 litre (or even 4 litre)  is still sufficient for single panels.

What are the other items in the Pressurised System Kit for?
Pressure Relief Valve
This provides essential protection to the system in the event that the expansion vessel fails. If the system pressure reaches 3 bar, the valve will automatically vent excess pressure in the form of water/steam into the overflow pipe to the outside. (Use copper pipe for the overflow). The valve also incorporates a manual operating knob - useful for venting and flushing the system during commissioning.

Filling Loop
Used to fill the solar system with mains water. Consists of a mains water valve and double check valve connected via a length of flexible braided hose. To comply with Water Bye-laws, the hose should be removed once the system is filled and vented. The check valve prevents contaminated water from the solar system re-entering the mains water supply.

Pressure gauge
Indicates the system pressure. System should be filled until the gauge pressure is slightly above (+0.2 to +0.3bar) that of the Expansion Vessel pre-charge pressure to allow for system contraction after filling.

Can I use pipe-lagging left over from my central heating system?
The solar loop can reach high temperatures (in excess of 100 degrees C). This will melt standard pipe insulation.
Navitron supply Armaflex HT pipe lagging that is designed for high temperature applications. This is essential on the flow pipework and preferable on the entire system.
If 10mm pipe is used, both pipes can be fed through a single section of 15mm ArmaflexHT pipe lagging. Close contact between the pipes will not be detrimental to the system performance.
Pipe lagging can be supplemented with an over-wrap of ‘Rockwool’ (or equivalent) within the loft space for added insulating properties if desired.

Can I use an automatic air vent like on my central heating system?
These are not recommended for the same reason as with the lagging above; the plastic components in the vent can melt!
It is preferable to use a radiator type manual air vent. A somewhat cruder method is to simply vent the system by slackening one of the manifold joints until non-aerated water flows - although this is not so practical if the system is also being filled with anti-freeze.

What pump do I use and what speed should it run at?
Any standard domestic central heating pump with isolating valves is suitable.
There is only around 1.5 litres of water in the manifold and the total water content of most systems will only be five to eight litres. Therefore start at the slowest speed position. Excessive flow rates will reduce the effectiveness of the high-efficiency solar coil in the cylinder.

Do I need a Thermostatic Mixing Valve (TMV)?
An optimised solar system will easily produce a cylinder of hot water in excess of 60 degrees C during the peak summer months. At this temperature, scalding is likely and is inevitable in the case of the young or elderly.
Therefore fitting one (or more) TMVs to the hot water supply is necessary. Valves compliant with the industry TMV2 scheme are suitable for domestic installations.
It is recommended to research the flow rate achievable through the TMV in conjunction with the water pressure (head) available prior to purchase. Some TMVs are only capable of delivering adequate flow rates to a single point (i.e. one tap) and are not adequate to supply the entire property direct from the cylinder.
A single common TMV needs to be a DN20 (3/4") TMV complying with BSEN1287 for bath fill applications. For an example of a suitable valve see  ** These are now available from Navitron **

Toolstation offer the RWC  Heatguard BF2  TMV2 4-in-1 TMV and this is another example of the type of TMV required to maintain flow rates to high useage fixtures such as baths.

Also be aware that any if plastic push-fit fittings are already used within the DHW installation they are usually rated for 65 deg C maximum. Therefore the distributed water temperature must not exceed this temperature.

How do I make the holes in the roof tiles?
The quickest and simplest way is to use an inexpensive tungsten-carbide tipped hole saw designed for concrete/brick. This will guarantee a clean hole with no breakages or chipping.
A masonry drill can be used with care – i.e. at slow speed and definitely not using hammer-action!

Also drill a separate 5-6mm hole (with a standard masonry drill) about 20mm in below the manifold flow pipe to take the temperature sensor cable. It is better not to use the same hole as the pipe - for one thing it will be a tight fit possibly damaging the insulation, and secondly the direct heat could cause degradation of the cable insulation in the longer term.

How do I seal the holes in the roof tiles?
Standard external silicone sealant works just fine on thick concrete tiles. Ensure that the drilled hole leaves sufficient gap around the pipe to ‘fill’ the full depth of the tile. Do not make the hole so tight that only a ‘smear’ is possible around the surface, as this will not bond to the tile as effectively. The lagging around the external pipework will prevent sunlight from reaching and degrading the silicone.
Note: For thin tiles and slates this method is insufficient and a proprietary or custom flashing must be used. Also some high temperature silicone sealants can react with concrete and are not suitable.

« Last Edit: June 17, 2011, 10:38:26 AM by Antman » Logged

20 x 47mm, 172 l cylinder, Heat Dump, 15 x Sanyo HIT-H250E, SB4000TL,  Nestor Martin IQ13 WBS
DIY Solar System Support at
All support is voluntary and free of charge. I'm not employed by Navitron so responses may not be same-day
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