Jeff Rychwa

That's exactly what it is: a bell.

The insulated riser off the stove really drags the air-feed, and the bell gets super hot. The exhaust off the bottom of the barrel (which is standing upright over the stove, still, as in the pics above), needs a "T," as you mentioned, but that cooler exhaust really is being pushed upward and out the thimble. The external chimney is insulated, too, so that is assisting with a pull, but certainly the external chimney doesn't seem to be sucking all the heat right out of the stove to warm the yard.

My favorite part--about which I've gone on, I know--is that the exhaust at the top of the chimney(s) is predominantly heat/vapor with little- to no smoke at all. I'm stoked. Just seeing that and knowing that I'm getting a really efficient burn (regardless of heat loss for the moment) makes me happy and hopeful, regarding the limited pollution and resulting limited need for excessive tree death.

I posted a flyer at my general store to get people who are dumping off brush piles at the dump to bring them to my house instead. I can feed both stoves branches, and I could, potentially, pass the word on Rocket Heaters to folks so that more people will get on board.

I managed to get 7 kiln bricks into the fire-box.

The temp at the top of the barrel hit 500ºF, while the pipe just at the wall thimble was at 250ºF. That tells me that the surface area of the barrel, plus the 6' of 6" exhaust pipe are radiating enough BTUs to reduce the exit temp by half of the barrel temp. That's pretty neat. But I still want to be able to recover more heat.

I'm just so blown away by looking at the top of both chimneys outside and seeing virtually no smoke at all. Unfortunately, I do see the waves of heat emanating from them, but, still...

On the dryer point, though, I've vented mine into the house using a home-made heat exchanger.

This is in my basement with the rocket stove and a dehumidifier, though, which helps to keep things dryer; although, this exchanger doesn't put out much ambient vapor at all.

I put a two-foot section of three-inch diameter pvc on the end of the dryer's flexi-hose with duct tape. I have a steel bucket [read: trash can] with a lid. The lid has a hole in the middle through which the pvc drops in and rests on the bottom of the can in about an inch of cold water. I put three, 3/4" holes in the end of the pvc sitting in the water, about an inch from the rim. These help to allow air flow into the water, especially if the pvc sits flush against the bottom of the can. (I typically tilt the can a little by placing a piece of something under one edge.

I put a hand-towel around the gap between the pvc and the edges of the hole in the top of the lid to aid in trapping vapor.

So the majority of the dryer vapor hits the cool bucket water and condenses in the bucket, while the heat escapes from some gaps (like where the lid "seals" on top of the bucket), and radiates from the bucket, as well. The moisture is extremely low.

The thing is that you need to make sure there isn't too much back pressure to prevent the dryer from exhausting properly, or you'll end up having to run it multiple times.

My dryer has always needed to run twice to dry a load, even while venting outside in warmer weather. It still runs twice to handle a load with the exchanger on it. A better dryer might be more efficient, obviously, but the exchanger seems to have no major, detrimental impact.

Hi, Nancy.

I also live in NH. It is legal for renters to have a wood-stove as a primary or secondary source of heat, but the landlord has to approve it, which means having an insurance company inspect it so it can be covered in the insurance policy held by the property owner. This is something you'd probably have to reimburse, at least a portion, perhaps, in the rent.

Otherwise, if you're living in a house that gets water (mold danger), and you're venting a dryer inside (more moisture and mold danger), and the house is not well-insulated, plus it's costing an extra $650 per month for heating it in the winter, I'd suggest forgetting the audit and move. Seriously. It sounds like you'd save money in renting something safer and warmer rather than spending it on sketchy heating methods that aren't reliable. (What if we lose power, which is the rule in New England winters?)

It helps to seal drafts in order to maintain heat, but in your situation, I'd be worried about sealing in moisture and mold, at least. If you can't move presently, then an energy audit is the LEAST I would have done.

Thanks, folks.

So, as an update, I took the feed-chamber and burn-tube out of the wood-stove. It was working well as a rocket stove, but I had to feed it small sticks (like half wrist diameter at most) every ten to fifteen minutes.

I turned the wood-stove back into a wood-stove, but I left the insulated riser and barrel on.

It works amazingly. I'm astounded.

The mini-rocket stove that it was put out about 150ºF as an average, 200ºF being the hottest I could get the top of the barrel. As a wood-stove with riser, it puts out 400ºF on average, with 500ºF being the hottest it's reached with one armload of dry sticks that are forearm sized.

The exhaust out the chimney is almost no smoke at all, just like the basement dragon. So between the two, this house is quite toasty, quite quickly, on much less wood than I used for the non-riser-and-barrel wood-stove.

I did the very thing, building in the basement, but I didn't couple the heater to the walls. The burn chamber floor is a layer of kiln bricks directly on the concrete floor, so the floor heats up pretty nicely, acting like a thermal battery. After the fire is out, even eight hours later the floor around the base of the heater is still warm.

I keep the heater running all day so the entire basement acts as my battery, then the stored heat just kind of emanates [convection] upwards through the night, keeping the second level around 65ºF even when it's well below freezing outside.

The rocket heater in the basement is running full-burn throughout the day, which cuts the humidity considerably (my dehumidifier is only being emptied every 3 or 4 days now, rather than every day). The vapor from the dryer is hitting the cooler barrel and the cool water within, so the warm vapor condenses quite nicely. Little- to no vapor is visible coming from the small gaps around the lid of the barrel, and anything that does escape into the basement air is negligible, especially considering how much vapor was down there prior to the heater running and the dehumidifier running. A shower puts out way more steam than the attachment on the dryer does, so I'm pretty confident that the moister problem has actually been reduced, and the added warmth to the basement as my "thermal battery" is helpful.

I have to add that I did not have the heat-exchange system set up on the dryer prior to the heater and dehumidifier running. The natural moisture in this basement is pretty intense. I was very worried about the dryer's added moisture, but it is proving to be a non-issue.

Hi, John. Thank you for responding.

I don't have the necessary equipment, yet, apparently, but now I have some direction.

I wanted to figure the force involved in order to be able to calculate, for future builds, the proportional amounts of exhaust pipe, riser heights for different cross-sectional dimensions, outdoor stack heights, etc.

This is completely new territory for me, so I'm throwing in a bunch of questions that are just brewing as I play with the concepts, and I really appreciate your taking the time to offer some guidance. This will help me start to make sense of what's coming together in my observations and future plans.

I'm wondering if anyone can lead me to some of the math that goes along with the thermodynamics of heat exchange, pressure, dispersal rate, force in different diameter flue pipes, etc. I would love to be able to calculate the flow of heat in my systems and possibly what I'm losing out the exhausts, not to mention the efficiency of what I'm gaining (I hope) as radiant/convection heat in the living-space.

To begin with, one of the goals of an RMH is to surpass pyrolysis, which means reaching a burn temperature over 250 dF, yes? And this is in the burn chamber, or is it a secondary burn in the riser?

I'm also curious to see how many Newtons of force push the heat through the pipes and out the stack, which determines how hot I need the burn to be. Has anyone gone here? Has anyone been able to calculate, with any degree of accuracy, the BTUs of their homemade systems in order to determine efficiency?

Thank you for the feedback, Allen.

A "T" is a great idea. I'm going to try to install one with a sort of ash-screen on the upstream side.

It occurs to me, because I already went through the days of construction and firing a barrel already, that I probably could have gotten the same (if not better) effect by just running a row of 6" pipe right off the riser up and down with a bunch of 180 degree joints (about 20' worth) rather than have the barrel at all, just like a giant radiator. <sigh>