Current Goal: Keep my House Warm

First, a bit of history about heating here in my house.

Initially, somewhere around 25 years ago when the (one-family) house was built (near Graz/Austria), there was only one way to heat: OIL. The situation has changed slightly, there are many alternatives like ground heat. Those are not exactly cheap, and oil companies are still permitted to give financial incentives to the undetermined.

A few years ago, I decided to establish a second heat source: a wood stove in the living room. In addition to its nice looks, it can feed heating water into the system, in parallel to the oil heating. The stove is used as often as possible (I work from home as much as I can), and only when there’s nobody at home the oil is on.

So far so good. Should be easy to control.

  • Two heat sources

    • Oil (fully automatic)

    • Wood (manual firing, in the living room). Wood currently dominates oil in a brutal way, in that a bi-metal temperature switch disbles oil burning abruptly when wood is coming.

  • Two heat sinks

    • Water; a 1000l buffer, where potable water is exchanged through

    • Radiators across the house, in a single circuit


But no: When I take a step back and look at the workarounds in our heating system, I can see that software is harder than hardware. It is common knowledge among plumbers how to install a wood oven alongside an oil burner, without touching the existing heating control.

Since I started to think about this project, I have seen many house heatings built around a software that cannot be modified. This aberration - software harder than hardware - is not specific to house heating systems, as it seems. This little project is my contribution to revert that aberration.


While the main impetus for this project is to bring my own system to its intended functionality, a definitive intent is to keep things apart as far as possible. Components on the horizon (or even yet in place; I do not update written material regularly):

  • Sensors all over the place, fancy histograms on a web page (done).

  • Switch pumps on and off, based upon temperatures in the heat source and heat sink (done).

  • A combined heat source which contains oil and wood (yay overengineering), and acts as one single heat source to the rest of the system.

  • Inside that combined heat source, one mixer valve that adjusts its position according to the respective temperatures of oil and wood.

  • Ah yes, error management (in fact, I started with that) (partly done).

  • Did I forget something?