Gravity Networks

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This page covers a specific design whereby a building heat network is fed using gravity circulation without the need for pumps.

At first this sounds like a madness, however it has been done in reality by mistake and has worked.

The idea is simple, however nobody would ever take such a design risk, so it was a lucky mistake when three tower blocks in London were found to have been running for 3 years without any central pumps installed.

Quality is such that nobody noticed the flaw in design. Heat circulated, and taps and radiators were hot. There were constant problems with air locks and this had been a continuous mystery to a stream od consultants who never took physical DP readings, but rather went by pipe temperatures.

If such an approach was designed for, then it is believed that problems could be removed and function perfected.

This worked in tower blocks with a roughly 20C drop on pipework generating enough head to circulate water to ground floor plantroom through oversized pipes.

We are aiming to do a system with a 40-50C drop, thereby significantly improving differential pressures generated through gravity effects.

The reader should note that as the experts in wood burner thermal storage we are well versed in the limits and methids of grsvity systems. They are not covered in any guidance, wit the only rules coming from HETAS guidance on wood nurner installations, where gravity curcuits are a safety requirement so as to remove heat from an appliance during power cuts when a pump will not function. We are simply applying this technology to a building with CO2 heat pumps at the heart rather than a wood burner.


  • A building network would be extremely reliable and efficient if pumping is eliminated, wth no moving parts to go wrong.
  • Assuming buffer storage is on the same level, use of storage would be self balancing.
  • Decentralised networks, with buffer stores acting as interfaces from pumped heat sources loops into building graity loops.


  • Risers should be of a diameter and level of insulation that will not cool down more than 10C over 8 hours. This is to overcome the need for recirculation to maintain flow pipe temperatures overnight. 54mm would be a minimum.
  • Central heating must utilise return tem[erature limit valves set to 35C maximum.
  • HIUs, or zones of load (e.g. a floor) are fitted with inline shunt-pumps on the primary to overcome HIU pressure losses.
  • No valving other than full-bore isolation.
  • No sharp elbows, with gradual bends in pipes and continuoys rises throghout. All horizontal runs need to be at a slight incline so heat is continuously rising, and cold dropping.