The water from the outdoor unit on an ASHP is pure water condensing on the cold coil from the surrounding atmosphere and is completely natural. But how should your installer have dealt with it?
We compared the installation guidance and standards for air source heat pumps and boilers to find the answers. We looked at the MIS 3005 incorporating the ASHP side and the BS 6798 covering the installation of boilers not exceeding 70kW.
Both technologies produce condensate, although the composition of the condensate is different. Boiler condensate is acidic with pH levels of between 3.6 and 4.2. The condensate from the outdoor unit on an ASHP is pure water condensing on the cold coil from the surrounding atmosphere.
- Domestic boilers can produce around 2 to 3 litres of condensate per hour
- Annual volumes of 600 to 1,000 litres per year
- Boiler produce condensate inside the building envelope and tends to be between 20 oC and 40 oC
- Boiler condensate is acidic and can only go into the waste water system. You must neutralise it before it goes straight to ground, into a rain water pipe, or sceptic tanks.
- The use of a soak away must incorporate lime chipping as a form of neutraliser and to provide void spaces to allow adequate drainage.
Air Source Heat Pumps
- Units upto 14kW can produce between 10 and 15 litres of condensate per defrost cycle
- Annual volumes of 2,000 to 3,000 litres per year
- ASHP produce condensate outside the property and can be between 3 oC and 5 oC
- ASHP condensate is pH neutral and can go into any suitable drain
- The use of a soak away is also acceptable. This does not need to incorporate lime chipping, but the material must have some form of void space to allow for adequate drainage
What the regulations say:
MIS 3005 4.4 Site Specific Issues states: For air source heat pumps, consideration should be given to the removal of condensate water produced during a defrost cycle from the outdoor coil. The installation should make provision to deal with this water transferring it to a suitable drain or soak away thus preventing ice build-up within the unit or its location during extreme winter conditions.
The regulation helps avoid the risk of standing water. This can pool and freeze causing a slip hazard on paths and walk ways around the heat pump.
The boiler standard BS 6798 covers a range of routing options. The options reflect the differences between ASHP and boilers.
Heat pump condensate has a lower temperature than condensate from a boiler. It is important to have a large diameter pipe (The minimum is 32mm) and as steep a fall on any pipework as possible to avoid the risk of the pipe becoming frozen.