With temps around 12 outside right now, it’s about 75 in the house and about to get warmer. I’ve just put a new load of wood in the fireplace to make sure the cold stays outside.
It occurs to me that running a wood fireplace is not necessarily an obvious thing. I had a bit of a learning curve from when I first got it 6 or 7 years ago. In that time, it’s easily saved us thousands of dollars in heating costs. Our oil tank only gets filled about 3 times a year and of those times, only the fall fill-up is a big one because the April fill-up lasts until about November when there’s only a few gallons left in the tank. The fill-ups we typically get in January and April are just toppers because our fireplace heats the whole house.
Our fireplace is a 75,000BTU model. It has a blower for a heat exchanger and a single air-flow control rod to control the burn. It is designed with airflow tubes across the top of the fire-chamber to achieve a secondary burn of the gases of the wood as they burn. When everything is running right, and hot, no smoke comes out the chimney because it all burns inside the fire chamber. Properly run, I can go 8 hours between wood loads, as the literature says. Though when it’s real cold outside, I find it better to load more frequently.
This model has no grate for setting the wood on. The firebox is lined top, bottom and sides with firebrick so the wood sits on a flat surface while burning. In order to get airflow around the wood to promote a good burn, a little care has to be taken when loading wood. First and foremost, do not just set the logs on top of the coals. This arrangement provides for no airflow around the wood and will smother the coals. The result will be wood that basically smoulders and delivers little heat and a lot of smoke with no secondary burn.
The simplest arrangement I’ve found is to push the coals into a pile into the middle of the firebox, trying to separate the ash off to the sides (or removing it entirely if there’s a build up). Then, place a pair of smaller logs on either side of the coals. Finally, push a couple of logs on top of the other logs and try to provide for an air gap between the coals and the wood. This is basically a log-cabin arrangement and it will burn very well with NO maintenance or futzing about with the wood for it’s entire burn cycle. Depending on the size of the logs, a third, cross-layer of wood can be placed on top of the second layer.
Which brings me to my first counter-intuitive observation of burning wood: quantity does not equate to peak-heat. That is, more wood does not mean that the fireplace will get hotter. It means it will deliver whatever peak heat is attained for longer. The peak heat is controlled mostly by the type of wood burned. It’s also controlled somewhat by the airflow control.
Which brings up the second counter-intuitive observation of burning wood: less airflow means more heat. There are 2 reasons for this. The first is that letting less air into the firebox means less cold air in the firebox to cool things down. The second is that it promotes more smoke from the wood, which ignites in the secondary burn and provides more heat. When I’m running the stove at it’s best, the airflow is closed down at least 3/4 of the way. How far airflow can be closed down depends on the type of wood, how well it is seasoned and how cold it is outside.
Oak, maple, birch and ash are generally all good burning wood. At least, those are the ones I have the most experience with. Birch burns the hottest, followed by maple, oak and ash. The longer any of these wood types has been seasoned and the colder it is outside, the more the airflow control can be closed down because the heat in the firebox will promote a natural draft that will pull in enough outside air to maintain an optimal burn.
A third counter-intuitive observation of burning wood is that more wood does not necessarily mean a warmer house. Here’s the thing: if I load the fireplace to it’s maximum volume and allow that to burn, I’ll get a long burn at peak heat. But I’ll then have a long period of time (up to several hours!) after peak heat where there are hot coals to burn off before enough room is available to fit another load of wood. Depending on how cold it is outside and how well insulated the house is, the house will being cooling off at some point after the stove naturally begins cooling down from peak heat. If there is a long time to burn off the wood coals that remain after peak heat, the house will cool off quite a bit.
Therefore, in order to keep the house at it’s warmest possible, I have to load enough wood such that peak heat can be attained and the house warmed, and the wood be consumed enough that another load can go in before the house cools down too much. This means it’s actually better to load slightly smaller logs more often (ideally every 3 to 4 hours) into the fireplace. This is why I’ve also found it better, from a burning standpoint, to have more smaller logs on hand than larger ones. Something to keep in mind when splitting cord wood.
How hot is peak heat? From the blower perspective (which is what does the lion’s share of house heating) the air is too hot for me to keep my hand in front of the blower for more than a moment. I measured it around 200 degrees with a temp probe. Usually, the door temperature is around 350 degrees Fahrenheit at that point. It doesn’t take a lot of that heat to warm a house significantly.
Stay warm out there.