Vehicle Rotors on top wood stove?

Do you think adding rotors on the top of a wood stove would be a good idea for heat exchanging/retaining or should I just stick with firebricks/thermal mass?

I have a wood stove in my roughly 450-500 sqft detached garage (converted from a chicken coop in the 1970s), which has very poor insulation. I'm slowly working on the insulation aspect. I live in Massachusetts, so winters here can get cold. I'm not out in the garage daily so I like to get heat quick. I had the rotors laying around so I figured they could help with a some heat exchanging, so I put them on top of a single layer of firebricks. One of the issues is, rotors are designed to dissipate heat, so retaining heat could be an issue especially if I'm not out there for a day. I do have a ton+ of different style landscaping bricks that I could try out too. I burn about 1.5-2 cords a year, so I'm trying to find a way to reduce that.

I say if you've got the iron mass laying around, use it. It will be interesting to see how much difference it makes in the temperature. If it doesn't make a difference, you can always take them off. I'm curious why the bricks are between the stove and rotors?

Ooo, an experiment! Any time you can capture heat in mass instead of air, you're ahead of the game. I think I would put the rotors right on the stove for best condutctivity, and maybe loose stack any bricks you have around it.

Bonus points if you put the chimney flue gases through some sort of thermal mass capture thingy. Folks around here say that's where the money is.

I was going to suggest adding a bunch of old computer heat sinks to the chimney stack along with some of the heat driven fans to push air over them.  Alternatively, you could look at adding a cob oven and make pizza for lunch :) while using some of the coal from your wood stove.

Great idea!  Adding the mass should result in a positive payback.

Jordan Holland wrote:I say if you've got the iron mass laying around, use it. It will be interesting to see how much difference it makes in the temperature. If it doesn't make a difference, you can always take them off. I'm curious why the bricks are between the stove and rotors?

I added them to increase airflow there's 1" gaps in between them. I was trying to get heated air to circulate through the center of the rotors, you can actually feel a slight amount of air flow and see it when you put a piece of paper over the holes, but that could just be normal heat rising. I cover the tops with old parts from the original wood stove, that was here when I bought the place 10 years ago, to try to retain some heat. I have to get creative a lot with this property, it was built in 1770 (chicken coup to garage conversion was in the 1970s). The prior family had it for a few generations and has sent me the old pictures they had from the garage conversation. I have just under 2 acres, I'm always finding items in the nooks and crannies... Especially when I have to dig for projects.

I'm going to try to put the rotors directly on the top to see if there's a difference at some point... Once my wife stops getting curbside found Christmas decoration for me to fix and she wants a light/sound christmas light show this year! I got off topic... lol... Some people have to-do lists... mine is a novel!

I appreciate the input! The members are great here!

That does sound like it would heat them up faster, but I also understand the concern of them cooling too quickly as well. My wild guess is it might also limit the maximum  temperature the rotors reach as well. It looks like a relatively easy experiment to tinker with to your heart's content. In your spare time! 😂

The best way to know what is going on is to have a laser temperature gun and record as much as you can.

The reason rotors dissapate heat quickly is because of the hollow core with fins that draw air through them. If they are not on a car, they are just heat sinks

If you want heat quick, think about a car radiator, as it is designed to dump heat as quickly as possible.  Lots of thin metal and airflow to dissipate heat quickly.

The heat coming off the top of your stove has already been transferred to your garage.  Like Douglas said, you need to capture more heat from the flue gasses to increase efficiency.   I like Lisa's heat sink idea.  They also made commercial heat exchangers that fit in a flue stack.  Another simple method is figure out a way to lengthen your stove pipe inside.  Beware that lengthening, slowing, and/or cooling flue gasses can result in creosote buildup and increased chimney fire risk. The solution to this is to split wood small and only burn it bone dry, being careful not to over fire your stove.  Your wood should always be bone dry, as it takes a lot of energy (wasted heat) to dry out wet wood.  Store your wood under cover, with good airflow, for at least a year, longer if possible.

For now, I'd focus on sealing and insulation.  You'll see more improvement from that than you would a few percentage points in efficiency on your stove.

The rotors directly on top of the stove will absorb heat faster than with the brick layer. I would put the bricks on top of the rotors to help hold the heat for slower release as you seem to want some warmth overnight. Steel conducts heat fast enough that its thickness will hold heat for a few hours at most. Putting stones & gravel in the rotor cavities would add slow-release mass without more bulk, and as much brick as you can fit around and behind the rotors will help.

I would check the stovepipe temperature where it goes through the wall/roof (or into the insulated chimney), and only try to recover heat from that if it is at the upper range of temperature, say more than 450F. You don't want to risk a chimney fire, especially with old wood structures. From the look of it, the stove is some decades old and maybe not very efficient, so I think you would benefit greatly from replacing it with a rocket mass heater. You could make one with two barrels stacked for maximum instant heat, and some bell mass for storage and modulating the temperature. You could even adjust this by partially cobbing around the barrels until you find the right balance of instant and retained heat. (Just be sure to allow for access to the heat riser inside for inspection.) The RMH could be built up to the brick surround, so not need to take much more floor area than the current stove.