Plumbing Design

Mains Water Plumbing

Initially when researching the options available to plumb the house I came across two  main methods- Pressurised/Closed or Gravity/Open. I settled for a gravity based system because of the simplicity, DIY, reduced parts and maintainability. If one can increase the height of the gravity tank the pressure will increase at the taps.

Below is a video of what a pressurised/closed system can do (if it goes wrong and probably very rarely). When I was researching pressurised systems I felt that there seemed to be different ways of designing these and providing the necessary safety levels. I do not like systems where there are potentially hidden failures (when a safety device is supposed to work and does not).


I also was hoping to use gravity to supply the showers but it is becoming more difficult to find a good choice of shower valves and shower heads that work on low pressure .  The way around this to keep things simple is to install a shower pump in a central location for two of the showers (see below). One can then use a shower head that helps control the flow rate and keep the water use to a minimum.

For one of the showers I already have a shower valve and head that works well on gravity so I will plumb this separately directly from the tank (shower 3 in the layout below).


The plumbing layout for the house is shown below. (The toilets are fed from a separate gravity tank supplied by the rainwater harvesting system as shown on a previous blog.)

Gravity Fed Design


I am using Qual-Pex for the plumbing in the house. It varies in price so it is a good idea to shop around (The 1/2 inch varies from €70 to €200 for the same pipe). I ended up using 200 metres  of 1/2 inch and nearly 50 metres of 3/4 inch and 25 meters of the 1 inch.

The overflow from the tank needs to be well secured or finished in copper to ensure that if the tank overheats the pipe will not sag/bend or cause a restriction.

The brass fittings are cheaper than the quick connect so I will use these. One needs a good plastic pipe cutter as using a hacksaw is not feasible. I used a Ridgid brand plastic pipe cutter and I am very happy with the quality.

With a plumbing design one needs to ensure that the size of pipes are no bigger than they need to be. One reason for this is that the volume of water in the pipe will cool down and one has to wait for this to run through fully before getting hot water at the correct temperature.

I calculated that  10 meters of 1/2 inch pipe holds approximately 1 litre of water and 10 meters of 3/4 inch holds 2.3 litres. This gives one an idea if a solution is required and the wait time.

The cold water pipes will be insulated as I am concerned that condensation could occur on the surface of the pipe.

I also tried to ensure that the number of connections/joints are kept to a minimum and I tried to place these only at accessible points.

Logistics of getting hot Water to the furthest points.

The kitchen sink hot water supply is too far from the tank so I may develop an on demand system that ensures hot water is available once certain taps are used rather flushing semi warm water down the drain and a one or two minute wait for hot water. Installing instantaneous heaters is not economical.

This on demand system is used in the USA for closed systems and two companies have developed a solution. One is and The first solution costs around $660 -too expensive.

A way to solve this is only use one 12 volt pump and have a valve at each sink position. This pump will then feed into the gravity header tank rather than the hot water tank (I need to check the regulations) . I want to keep the plumbing connections and electrical devices to a minimum. The power to operate this can be a small solar panel charging a battery.

The plan is to develop a solution around the following -Measure the hot pipe feed temperature, Detect if the tap is going to be used and link this to controlling the pump and valve.

The only item that needs to be purchased is a 12 volt pump and a 12 volt valve and develop the control unit to suit the Irish regulations. I have started on the design of this. In the meantime I will install a third pipe in the bathroom and kitchen for the final solution.




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