Another RMH chimney question

I've been searching for methods to exhaust a RMH out my basement foundation (8" poured concrete).  Many of the posts from around 2017 and earlier state that the chimney can exit the foundation and just "poop" the exhaust on the ground.  Their word, not mine : )  I don't think that all the examples I read about were experimental or tests.

I'd like to hear about some experiences doing just this.  Exit out the foundation horizontally and capping off the stove pipe just outside the foundation.  I'm just a couple days from renting an 8" concrete boring drill to get a start on the heater.

Some details of my situation.  I am in northern Wisconsin on the MI border, so cold weather.  The RMH will be on the basement floor.  It will rise vertically about six feet from the mass, make a 90 degree bend below the ceiling and out the wall.  The horizontal wall portion would be around 24" before a simple DIY cap finishes off the chimney.  I can add an elbow and go vertically at that point and go straight up for up to ten feet in case the draw is not sufficient.  I don't intend to go through my soffit and roof unless absolutely necessary.  I don't know if adding the outdoor vertical section will cause drafting problems.  I'm hoping to avoid hundreds of dollars of insulated stainless pipe to go through the roof.  I do have a good supply of super wool to wrap the outdoor chimney for a few feet if that would help with draft.

I know that windows near the pooping area are not a good idea.  There are no combustibles outside that foundation wall.  The prevailing wind would carry gases away efficiently.  As a precaution I could rig up a solar powered fan just above the stove pipe cap to help stir the gases and carry them away from the house.

Thanks,
Tim

This method was developed by Ianto Evans in an area (coastal Oregon) which has totally reliable prevailing winds, and is probably only suitable for those conditions. If you ever have different winds during heating season, you would probably be very unhappy.

My RMH exhausts by a "temporary" 6" metal chimney on the east side of my house, and originally it stopped three feet short of the roof eaves because it was a three-story drop if I fell off the roof adding the last section. It drafted perfectly nearly all season, but in early spring there would always be a few days with easterly winds, and the heater would smoke back in puffs and snorts and make the place miserable. I would have to forego a fire on those days. Once I got safety gear and got on the roof to extend the chimney 2' above the roofline, there have been no more smokeback incidents.

You can try the horizontal exhaust, but be prepared to extend the chimney up to above the roofline, at least at the edge, if necessary. If your house is not fairly airtight, the whole house will be competing with the horizontal chimney for draft, and it is quite possible that you will get the house pulling smoke and even fire back into the basement and upstairs through the feed tube.

I made my 5' chimney extension with a 6" galvanized duct inside an 8" duct, packing the 1" gap with fiberglass to make an insulated system. Definitely against code and I would never do it for a woodstove, but with the low temperatures I have in the chimney, it works fine. Be sure to orient joints so the inner duct sheds condensation to the inside and the outer duct sheds to the outside, to avoid water getting into the fiberglass.

How wide is your roof overhang? Unless it is huge, you can simply extend the horizontal penetration far enough that the vertical from there will just pass by the soffit and not have to cut your roof.

Thanks for the input Glenn.

My eaves are 24" so going through should be no problem as far as framing obstructions.

Though the north side of my home is out of view for the most part I still don't want the "look" of an angled chimney just to avoid the work to penetrate the roof.  Going through the roof at the eave is not a problem but is not something I would be able to accomplish until summer.  Right now we have a little snow on  the roof and undoubtedly there will be more soon.  My house is very air tight.  We used to have a wood furnace thirty years ago which was our only source of heat.  When we turned on the whole house vac in winter we'd have to crack open the front door or the basement would fill with smoke.

If the pooping design does not draw well I can easily  extend it above the roof temporarily.  I just wonder if the interior (heated) six or seven feet of rise in the chimney above the mass is enough to draft outside.  I'm building a six inch J-tube with six inch chimney.  And, I accept the fact that I should do this properly... insulated exterior pipe and proper wall thimbles.

This all raises another question... aside from having active combustion air movement is exhaust from a properly designed and burned RMH a lot different from pellet stove emissions?  Those pellet stove chimney kits seem to just exit out a wall and mainly require defined distance from combustibles and window/door openings.  Is the key the combustion air fan?  Has anyone incorporated a forced combustion air system on a RMH?  

Tim

A properly designed and built RMH burning dry wood will be putting out warm steam, for the most part. So a fan-forced exhaust is certainly a possibility, as long as it doesn't mind the humidity and mildly acidic nature of the flue gas. Forcing air into the system is also an option, and some have done it, but this would make me a little more nervous about overpressurising the system and driving combustion gases into your living space.

Hi Tim;
Yes, pellet stoves can vent horizontally, and I agree the fan is making that a viable option.
Many of us have used a fan temporarily blowing in the primary air intake to help a cold RMH start smoke-free.
A few folks have even added a fan at the top to suck the exhaust out during warmup.
Both those methods are removed or turned off after the RMH is warm and drafting on its own.
The fan on a pellet stove remains running, so uninterrupted electric power is required.

Now let's talk about the differences between RMHs and pellet stoves.

The first difference is the volume of exhaust.  2or3 pellet's burning does not match what a 6" or 8" batchbox puts out in volume.
The next issue is the draft. The pellet stove requires a fan to maintain a draft and to supply pellets to the stove.
Some pellet stoves have a manual feature to sit and hand crank pellets in case of electric failure...   Imagine sitting all night next to your stove to crank in new pellets... I predict that by morning you will want another alternative.
Without power, the fan will not work. A vertical vent stove pipe would work fine.  A horizontal pipe might or might not work depending on the wind outdoors.
Most folks do have a gas generator for storm-related power outages and that is a noisy but viable option to maintain the pellet-generated heat in your home.
Now about putting a permanent fan on an RMH.
The idea of a mass heater is to save the heat... not push or pull it through the mass and eject it outdoors.
RMHs do not care if your power goes out, nor do they require hand cranking to feed...
However, the biggest difference, in my opinion, is that you can not sit/sleep, or hug a pellet stove!
Depending on the style, you can do either with your RMH!

Good info to think about.  I like the idea of a temporary forced air system just until a positive draft is created.  I imagine that turning on the fan about ten minutes before starting a fire would warm up the chimney enough to make fire starting easier.

I'm going to start there as I have the option to add vertical chimney if a draft gives me challenges.

First I have to get that concrete boring drill and get drilling.

Thanks

So Tim;
Here's the thing about properly built RMHs.
Depending on where you live, once you fire up the Dragon for the season and the mass gets warm, you never have startup issues again until you allow it to go completely cold the following spring.
Only a cold RMH might have startup issues never a warm one.

thomas rubino wrote:So Tim;
Here's the thing about properly built RMHs.
Depending on where you live, once you fire up the Dragon for the season and the mass gets warm, you never have startup issues again until you allow it to go completely cold the following spring.
Only a cold RMH might have startup issues never a warm one.

I've read that before.  Thanks for the reminder Thomas.  Maybe I'm worrying too much.  Since I have the option to extend the chimney vertically outside I should just get building.   : )