TLDR: Pyroclassic woodfire is efficient, but leave it burning 24/7 for best results. Will heat entire house if reasonably well insulated and draught proofed.
A recent project has been a major structural upgrade to our downstairs lounge and dining area – we removed two back to back open fireplaces and a wall with extensive storage cupboards on both sides between our lounge and dining room to open up and increase the size of our living area. At the same time we strengthened all the walls, fitted support lintels for the upper storey, and fully insulated the room, then restored and reinstated the original rimu TG&V panelling and fitted a new ceiling. We installed a Pyroclassic IV woodburner in the same location as the original fireplaces, on a renovated concrete foundation with a mill finish steel hearth set flush with the floor. The structure around the fire needed to be retained because it supports the upper storey.
House is a 1920s California bungalow, with an upper storey added in the 1980s. Timber weatherboard, steel roof, single glazed timber windows, various degrees of insulation (varying from none to the maximum possible for the construction). Very sunny but exposed and windy location.
We recently traveled away for a few days, so were able to observe the effects on house temperature as the woodburner was shut down and restarted.
This is the context of the installation (click on images to embiggen):
We were away from Monday to Friday in early September, and let the fire go out before we left. Normally the fire runs 24/7 with no problems – in fact it is easier and warmer to keep the fire going for months at a time (we lit the fire in June, and let it go out in September). We find that the fire generally heats the entire house – we have a heat transfer system that can duct excess heat to the upstairs lounge if we are using that room; our house has always been difficult to heat previously, as it has a lot of open doorways and open stairs.
There is a temperature datalogger in the lounge, some distance away from the fire as shown in the image above. This recorded the data for the period we were away, shown in the chart below:
The Pyroclassic is a massive (but small) woodburner that takes quite some time to heat up, and can be difficult to start from cold, so we’d always felt that to get the best out of the Pyroclassic you need to keep it burning 24/7, and the chart seems to confirm this. The chart shows that after letting the fire go out, it takes some time for the room temperature to fall to the ambient level, and even longer to climb from that level to the normal operating range for our house. For example, it took an evening to heat the room to 20°C, and a further day to achieve 24°C. This is heating not just the lounge, but the entire house indirectly.
It seems better to keep the entire space and structure heated all the time, rather than restarting the fire every evening. We’re fortunate that we can keep the fire going 24/7 since we can add fuel at lunchtime if necessary, and we have enough storage to keep the firewood we need. The Pyroclassic is quite efficient, we burn a mixture of gum and manuka, and a couple of short manuka logs will easily burn at least 8 hrs, and still be hot enough to immediately start burning new fuel when it is added to the fire.
Most of the house heating comes from the Pyroclassic, our power usage over the same period is shown below. Background power consumption is 500W, and we normally use an additional 500W when we are home (and none of this is space heating), and I don’t believe this is a significant contribution to heating this area. Normal occupancy is two humans and one (or two) greyhounds.
Our experience with the Pyroclassic fire has been overwhelmingly positive. While it does require some organisation to get the best out of the firewood supply, and it isn’t the cheapest or most convenient way to heat the house, it produces more heat output than we would reasonably expect from even a large heatpump installation. Here are some tips from our experience:
- Use gum, manuka or other dense wood. Clean untreated unpainted demolition timber (rimu, matai etc – not pine) is also good if available. Cheaper woods like pine or macrocarpa don’t burn as long and so require more space for storage and more handling and stacking. Macrocarpa seems to attract more cockroaches for some reason.
- Use dry wood. The importance of this cannot be overstated.
- Condition the wood before burning. Design your fireplace with storage so that the wood can be dried beside the fire. There is a reasonable amount of airflow due to convection, and the sides of the burner do not get hot enough to be a hazard, but are very effective at drying stacked wood. Do not stack wood higher than the top of the burner as that would create a fire risk.
- Having enough fireside storage makes the task of managing firewood much easier, we only have to get more wood in every few days.
- Leave the fire burning 24/7, as it can be harder to start when it is cold and is more effective at heating if everything is kept up to temperature.
- Get in the habit of raking the coals forward before putting new wood in towards the back, but on top of the coals. When burning overnight the coals should have formed ash which you can remove the next morning. The burner doesn’t need a bed of ash to improve insulation, the ceramic liner does the same thing. The curvature of the liner also focuses heat into the new fuel.
- Even when the fire looks like it is nearly out, putting good dry fuel in it and leaving the boost control shut should get the fire going, it may take 10 minutes or so to show flames.
- Burn logs in pairs. This increases the surface areas that start burning, since the logs quickly start burning on the two centre faces.
- Be careful with the old ashes, they are a significant fire risk. We keep a stainless steel bucket on the hearth to put ashes in, and empty the bucket every few weeks.
- Consider using the top to cook on, it is very effective. You will need a trivet to reduce the heat transferred to your cookware.
- Expect the amount of dust in the house to increase; you will also have to deal with some mess around the fire, so having an easy to clean hearth is worth considering.
The lounge renovation, insulation and particularly the fire installation have totally transformed the house. Previously the entire downstairs area was quite cold and damp, and difficult to heat. Now it is spacious, light and very warm, with the normal temperature range, even in coldest winter, lying between 20-25°C.
Pyroclassic woodburner website: http://www.pyroclassic.co.nz/