storminnorman

That is very interesting. Can you verify that the fan blades are spinning in a direction that would push air? If the thermocouple was installed upside down or the wiring on the motor swapped, then the fan might run in reverse. Similar to how people reverse ceiling fans in the winter. In that case you might not feel any wind in front of the fan. If you’re not sure. Try the ember test behind the fan?

I see. Maybe if I had googled “ecofan test” instead of “ecofan thermodynamics” I would have found that thread first. Thanks very much for the link.

I've been thinking about buying an ecofan for my FIL's cabin and, being a skeptic, I googled "ecofan thermodynamics" to see if people have done any kind of analysis before I make a decision. Well, this was the only thread that came up so I find myself in a boating forum even though I don't (yet) have a boat. There's been some interesting discussion on this thread, and a good mix of people for and against using an ecofan. I've thought about the original topic enough to sort of come to an opinion so I thought I would add here to see what you all think. Let's start simple: a wood stove by itself. You burn wood inside - the box and the flue get hot. You feel warm when the heat transfers from the burning stuff to the box itself to the air surrounding the box and then finally to you. There's some radiative heat directly from the box, which hits you and the walls of the room, but we'll ignore that for now since that complicates things a bit. Now add a large heatsink to the firebox. Not an ecofan, just a heatsink the size of an ecofan. What happens? Now there's an additional path for heat transfer from the box to the air surrounding the box. The base of the heatsink creates a "cold" spot on the box, where heat will, excuse the semantics, sink into. This creates a larger heat gradient within the wall of the box. I'm not gonna get into the math, but when you have a larger heat gradient, you have more heat transfer happening. Great, more heat is transferring from the fire to the box. And obviously the heatsink is dissipating heat with its large surface area. So it's like the firebox has a little bit more surface area to release a little bit more heat. Where would that heat have gone if not for the heatsink? When the box is at steady state (heat from the fire to the box = heat from the box to the air), most of the excess heat would have traveled up the flue. Now turn that heatsink into an ecofan. The heatsink starts to warm up, and a heat gradient forms at the choke point where the thermocouple is. The fan turns on and starts doing two things: 1) establishes a horizontal air current at waist height (where there normally wouldn't be) and 2) increases heat transfer at the heatsink by pulling in ambient air to be heated up. (2) will cool down the heatsink further so now there's a greater heat gradient at the foot of the heatsink and therefore more heat transfer from the box. And (1) is a tricky thing to discuss without doing simulations because it depends on the size/shape of the room how helpful it is. For a stationary person who can sit in front of the fan that'd be nice, but I think it's important to think about performance/output and whole room heating for a given amount of wood. However, we do know that hot air will rise and it will generally stay on the ceiling unless something pushes it around. For a fan-less room that would generally be from more hot air rising up or people moving around. That seems inefficient because the longer that hot air stays up there, the more it's going to leak heat out of your room (or boat). So I think the fan would improve the performance of the stove in that regard. In summary, it seems like the ecofan will increase heat transfer from the firebox to ambient air as well as help mix hot air with ambient air. But the Made in Canada version on Amazon is still $80, so if I was buying for myself I would have to consider whether those benefits translate to a reduction in wood usage and then how many cords of wood would this save per year. Thankfully, I would buy this as a gift so I don't have to think about all that. Back to the original topic of pointing the ecofan the "wrong" way, this is a tricky one. The ecofan is directing heat from the box back onto the flue where it would have been if there was no ecofan, but it's still acting as a fan to mix air / aid in convection. It's possible that the flue being warmer is enhancing the draft which increases burn rate and gives you a warmer room, compared to having an ecofan pointed way from the draft. This is a stretch because I would guess this back-transfer of heat is small compared to the amount of heat already in the flue that is coming directly from the fire. The other possibility is that for this type of room (maybe it's small enough or insulated enough), it's more effective to enhance the convective current than to disrupt it.