Masonry Mass Heating
Let’s get to J.R.’s other subject, a Masonry Heater for his new home. He has the basics right. The efficiency is much higher when burning the wood at a high temperature with air brought from outdoors directly to the combustion chamber. The heat is absorbed by the large mass of rock, block or brick surrounding the fire which, in turn, warms the home.
J.R. wants to bury the air intake pipe under enough ground to warm the air some before it gets to the fire during the winter. Then, in summer, air from the same pipe could cool the masonry mass.
But J.R. can avoid that extra work. The air intake pipe needs to only bring outside air of any temperature, by the shortest route, directly to the combustion chamber. Prewarming the air does not significantly change oxygen content or density of the air at the temperatures involved in home heating. And using the air from the same pipe for cooling the mass in summer isn’t necessary. I’ll get to that in a minute.
These heating systems are a lot of work to build. There has to be a mass weighing a number of tons of mostly stone, brick or block that is skillfully put together. Beyond that the builder needs to understand and accommodate the various functions of the parts in order for it to be an efficient heater. That is why you don’t see many of them around.
Your multi-ton masonry mass will be sitting on a concrete slab that rests on the ground. In summer the mass will conduct its heat down through the slab into the ground. Ground temperature stays within a narrow range all year. Here in our part of New England ground temperature under our foundation slab is in the mid-50s in late summer and may cool to the mid-40s in late winter. So when the masonry mass is no longer being heated by a wood fire it cools to near ground temperature all by itself in a week or two and automatically air conditions your home all summer. Actually, you and everything in your home are radiating heat to the masonry mass which is conducting it into the ground under your home. Kind of mystical isn’t it?
Right now it is 88 degrees outside. But our inside temperature is a bit under 60. Plus our air vents all around the house are open. This apparent anomaly is because the masonry mass cools (and heats) the home with radiant heat, not convected heat as are most “modern” homes. The above photo shows about one third of the 47-ton masonry mass in our 3500 square foot home silently doing its work without electricity.
So, J.R., put away the shovel. Find BHM issue #90, page 46, and BHM issue #91, page 8, and you will have all the information about owner-built Masonry Mass Heating and Cooling Systems you will need along with many peripheral details you might like. I have built, if I remember right, about 20 various sized systems like this, learning things all along the way.
If you can’t find the BHM issues mentioned, write again.
