In this podcast, Paul and Jocelyn talk about how they heated their home with only 0.6 cords of wood. They take the rocket mass heater in the Fisher Price house as a case study.
It is December in Montana and they only get about 6 hrs of sunlight at this time of year. Cloudy days seem to make the days feel even shorter. Montana days are cold and crisp unlike those in Seattle. The RMH used about 1/2 cord of wood and lots of people called Paul a liar. A cord is 4x4x8 so half a cord is 4x4x4. The fisher price house uses a pea gravel style RMH. Paul created a log to track indoor and outdoor temperature and the wood used for the season. 0.60 cords were used in 2016/2017. One person on the forums told Paul that they need to weigh the wood but Paul feels that weighing the wood is kind of silly. Most people measure a cord of wood by volume and not by weight. Paul likes the idea of measuring the wood use by volume and is not all that concerned with btu’s. What really matters to Paul is the use of the wood and how much is used. One interest is hardwood versus softwood and most wood around the farm is soft. There are currently 12 RMHs on the farm and a bunch of others in various states of completion. Paul does buy wood at times depending on priorities. Firewood is something that is gathered when time allows and sometimes it can take a long time. The last winter would have needed about 6 cords with a conventional wood stove. The house is about 1400 sq ft. It is a double wide and because it is not on a foundation it can be pretty cold. The RMH in the Fisher Price house is on the 4 dvd set. It has a stainless steel barrel. Pebble style is working very well. Not as good as cob but pretty good. Pebble is way more portable than cob. This RMH was built in October of 2013 and then modified in January of 2015. The modification worked well but the pebbles were added over the summer and now it is working great. The wood is stored in bookshelves/cubby holes near the stove. Jocelyn does not like building RMHs but she does like using them. Jocelyn likes the radiant heat. When it is cold at the house and the RMH is not run the forced hot air heater kicks on every 15 minutes and it sounds like a jet engine. The RMH is silent in comparison. The wood used is more sustainable as well. Other people in the valley create lots more smoke with their conventional stoves. The exhaust temperature is close to room temperature and is very clean burning. Starting the RMH sometimes creates a small amount of smoke if you use Ernie’s method. Paul and Jocelyn try to create a smokeless fire when they start by pushing the starter paper down into the feed tube before trying to light it. There is a discussion of paper towels and paper napkins that were recycled and how they are not good in compost. Paul’s preferred method is to use a propane torch to start his fires. The arc lighter is also a good tool to use to start the fire. Jocelyn prefers refillable butane lighters. A discussion of where the RMH is placed in the home begins and Paul does not like having the mass in the middle of the room. People tend to put laptops up on the mass and that’s not so good. Last winter had lots of days below zero and snow on the ground from November to March. The temp inside was kept around 69. The thermostat was set up in the dining room next to the kitchen. Paul wanted the thermostat to be influenced only by conventional heat. The floor had to be reinforced to hold the weight and this is covered in the dvd set. The RMH is not quite done yet. There is some granite still missing but they are working to get the last pieces of granite ordered and installed. As winter progressed they got more efficient at using the RMH. In the summer the mass acted as a heat sink. On days of feast people cooking would help heat the house so they did not need to use the RMH. Several windows in the house were frozen open which contributed to heat escaping the house. It was also important to leave a window open when starting the RMH. Once the fire is going fans can be on but at the end of the fire fans can draw smoke back into house.
Ash Jackson is The Scrollbard
I was just re-listening to this podcast and Paul talks about his idea to reduce the flue size after a series of bends near the exit of the mass (actually in part 2).
I was thinking that you could add a damper to the vertical chimney (after adding all the bends etc) to experiment on how much you could close it (reducing the CSA and establishing the optimum CSA)
before changing out all the pipe.