Home energy audit

Mindfully using energy is a key tool in solving humanity's environmental problems (see also this amusing yet insightful test). Doing so begins at home by using:

  • only the energy needed for reasonably comfortable living,
  • converted in efficient ways,
  • sourced from renewable sources,
  • produced locally, whenever it makes sense to do so, and
  • reused locally whenever possible.

While house shopping, a good insulation and heating system were among the key criteria. The one we picked has an A energy certificate and uses only electric energy, so we thought we were pretty close to our goals. We knew we wanted to optimize things at some point, but it didn't feel like a pressing priority.

An unusually cold winter outside (by Portuguese standards) felt cozy inside, but the first electricity bill shocked and spurred us into action. The Milkwood permaculture living course gave us the idea of a comprehensive energy audit, and the government of South Australia provided a handy checklist. This is a summary of the findings, actions taken, and next steps we're considering.

Energy source

Aside from a rarely used outdoor wood-fired oven and BBQ, everything is electric and solar.

Our electricity provider is Alfa Energia, chosen because they have a 100% renewable plan (which we use) and are Portuguese owned. They provide a breakdown of sources in each bill. It's typically 100% hydro, although the most recent bill shows a weird mix that is almost 50% of fossil fuel origins, mostly natural gas and coal.

Through SunEnergy (highly recommended - they were professional and efficient), we installed photovoltaic panels and batteries for storage. When the weather is not fully overcast, the system supplies almost all electricity for a 24h period. On sunny summer days, there is a lot of excess electricity (2-3 times what we consume) supplied to the grid via Energia Simples.

Energy sinks

Heating and cooling

Supplied by a ground-source heat pump and distributed through the house through underfloor radiators with thermostats in every room.


  • ✔ Only heating/cooling the rooms that are being used.
  • ✔ Most of the rooms have south-facing windows with shades that generally stay open during the day so the sun can heat inside. We'll have to be diligent about closing them in hot summer days to keep things cool.
  • ✔ Heating setpoint is relatively low, generally 20°C or lower. We might not run the system in cooling mode at all most of the time in summer.
  • ❌ Neither the heat pump nor the underfloor system have been serviced since we moved in.
  • ❌We don't use reversible ceiling fans to assist heating and cooling.
  • ✔ The home is insulated, although ❌ the window frames don't seem to be.
  • ❌The entrance doors have large enough gaps underneath to let significant draughts in. They face north, so the prevailing wind pushes cold air inside. Currents flow out of the kitchen and bathrooms exhaust paths.


  • Heating: ✔ the house was comfortable during the cold winter.
  • Cooling: ❓ we didn't go through a hot season yet.


  • Heating set points: it took some iteration, but managed to find a setting that is comfortable but not too warm.
  • Disabled "passive cooling" in the heat pump: at least during mild winter/spring days, there was no reason to run the cooling circuit and it used a small but significant amount of energy.
  • Integrated the room thermostats into Home Assistant to get data on temperature and humidity changes across time.


  • Service (or replace, if it comes to that) the heat pump. This has proven very difficult because Thermia (the manufacturer) is not officially present in Portugal and the local company that installed it went out of business. Nobody else wants to touch it and there's no reasonable way to get spare parts.
  • Service the underfloor heating system.
  • Install a mechanical ventilation system with heat recovery to increase comfort (constant fresh air supply, reduce indoor humidity) and reuse energy from heating/cooling the house.
  • (Better) seal the entrance doors and other air gaps to reduce energy loss.
  • Consider better window frames to reduce energy loss and avoid condensation.
  • Automate window blinds based on time of the day and season to make the most out of free heat gain and loss from the sun and to the outside.

Water heating

Solar heater with tank and electric auxiliary heater. Return circuit with switchable circulation pump to avoid wasting water while flushing out cold pipes.


  • ✔ We take reasonably short showers.
  • ✔ Shower flow rate is reasonably low.
  • ✔ The taps don't drip.
  • ❓ It's unclear whether the external hot water pipes are insulated


  • There was not enough pressure in the solar loop and the tank was corroded. All of the heat came from the backup heater. After servicing the system, all of the hot water comes from the sun on all but fully overcast days.
  • Set points: we don't need scalding hot water, and setting them lower reduces the amount of time the backup heater kicks in.
  • Circulation pump control: replaced the existing system with a Z-Wave switch integrated into Home Assistant. It can now be manually controlled (when we know we're going to need hot water ready for a shower), it turns itself off after a while to avoid wasting heat, and regularly turns itself on during the day if the water tank is hot enough.


  • Replace the auxiliary heating with something more efficient, ideally by having the heat pump supply it instead.
  • Check whether the external hot water pipes are insulated.
  • Smart control for auxiliary heating: it's now entirely temperature-driven, which means it can and does run during the night or when nobody is home. Both of those can be addressed from Home Assistant.
  • Smarter control for the circulation pump: with a temperature sensor on the return line, it could make better decisions about when and for how long to run.

Home appliances

  • ✔ We know or can easily measure power usage for each appliance.
  • ❌ We don't switch appliances off at the wall when not in use. Stand-by power is a small enough portion of the base load that it's not worth worrying about for now.
  • ✔ We generally wash dishes and laundry with full loads in the machine and with the coldest water temperature that will do the job.
  • ✔ We hang clothes out to dry.

Fridges and freezers

  • ✔ Fridges and freezers are only run when needed (e.g. those in guest accommodation).
  • ✔ Fridges and freezers are of the right size for the need, and energy efficient.
  • ✔ Fridge temperature is ~ 4°C
  • ✔ Freezer temperature is ~ -18°C
  • ✔ Fridges and freezers are located out of direct sunlight.
  • ❌ Ventilation could be better in the enclosing rooms (this should be improved by the MVHR system from the heating and cooling todo list).
  • ✔ Fridge and freezer doors seal properly.
  • ✔ The freezer auto-defrosts.

Kitchen appliances

  • ✔ The oven door seals properly.
  • ✔ We mostly use smaller kitchen appliances instead of the oven.



  • ✔ We generally don't leave lights on in empty rooms.
  • ✔ We use daylight instead of artificial light most of the time.
  • ✔ We use low wattage and energy efficient lights everywhere.
  • ❌ Outdoor lighting is not operated by motion sensors.


  • Make outdoor lights dim or turn off based on movement around them and on the luminosity.