Harmon MKII Backdrafting

Re: Harmon MKII Backdrafting

PostBy: freetown fred On: Sun Oct 28, 2012 8:18 am

I agree with the concept of the 8" going into an existing clay flue--it just strikes me that the independent 8" on this set up leaves a lot to the elements that can truly be to say the least, finnicky--I too would hope that another length of 8" will solve the problem-- I will do my--I hope it works--Native dance on my way down to the barn ;)
freetown fred
 
Hand Fed Coal Stove: HITZER 50-93
Coal Size/Type: BLASCHAK Nut/Stove mix

Re: Harmon MKII Backdrafting

PostBy: SteveZee On: Sun Oct 28, 2012 8:44 am

freetown fred wrote:I agree with the concept of the 8" going into an existing clay flue--it just strikes me that the independent 8" on this set up leaves a lot to the elements that can truly be to say the least, finnicky--I too would hope that another length of 8" will solve the problem-- I will do my--I hope it works--Native dance on my way down to the barn ;)


:lol: toothy :clap:
SteveZee
 
Hand Fed Coal Stove: Glenwood Modern Oak 116 & Glenwood 208 C Range

Re: Harmon MKII Backdrafting

PostBy: McGiever On: Sun Oct 28, 2012 3:21 pm

McGiever wrote:Looking at that roof pitch...I'd say you need more height.

And that 8" pipe is just fine for your sub-bit Alaskan Coal. :)


I add to what I said earlier...

This is a Pennsylvania made Harmon Stove being used in cold windy Alaska in an A-frame style home w/ sub-bituminous coal...I'm pretty sure the engineers had not optimized their stove for this arrangement.

Changing to a 6" flue will do little if anything, and probably actually make things worse.

It only back-drafts when the wind direction is from the one side and works fine other wise.

Only thing needing changed here is how the chimney behaves with that wind direction. :)
McGiever
 
Stoker Coal Boiler: AXEMAN-ANDERSON 130 "1959"
Hot Air Coal Stoker Stove: HARMAN MAGNUM
Hand Fed Coal Stove: RADIANT HOME AIR BLAST
Baseburners & Antiques: OUR GLENWOOD 111 BASEBURNER "1908"
Coal Size/Type: PEA / ANTHRACITE, NUT-STOVE / ANTHRACITE
Other Heating: Ground Source Heat Pump
Stove/Furnace Make: Hydro Heat /Mega Tek

Visit Hitzer Stoves

Re: Harmon MKII Backdrafting

PostBy: freetown fred On: Sun Oct 28, 2012 5:01 pm

Sounds like you're guaranteeing this :?: I guess I'm not that knowledgable about hand fired plus spending 2 winters in Alaska burning wood back in the 70's. I'm personally trying to help with the process of elimination--not living in dc's house, it's hard to do much but speculate.
freetown fred
 
Hand Fed Coal Stove: HITZER 50-93
Coal Size/Type: BLASCHAK Nut/Stove mix

Re: Harmon MKII Backdrafting

PostBy: Freddy On: Sun Oct 28, 2012 5:51 pm

McGiever wrote:Only thing needing changed here is how the chimney behaves with that wind direction.


I think I'd give those words consideration and sleep on them.
Freddy
 
Stoker Coal Boiler: Axeman Anderson 130 (pea)
Hot Air Coal Stoker Stove: Reading piece o' junk in the barn (rice)
Coal Size/Type: Pea size, Superior, deep mined

Re: Harmon MKII Backdrafting

PostBy: SMITTY On: Sun Oct 28, 2012 6:19 pm

Thinking outside the box here .... :o ... :lol:

Maybe take the whole cap off that chimney & try it. Maybe the design of that cap allows sideways air in? Like I said ....... just thinking outside the box. Won't cost much to try it.
SMITTY
 
Stoker Coal Boiler: Patriot Coal - custom built by Jim Dorsey
Hand Fed Coal Stove: Harman Mark III (not currently in use)
Coal Size/Type: Rice / Blaschak anthracite
Other Heating: Oil fired Burnham boiler

Re: Harmon MKII Backdrafting

PostBy: Lightning On: Sun Oct 28, 2012 6:54 pm

I agree with McGiever on this one.. My logic is that with that sharp roof pitch, air is piling up in front of that side of the house creating a subtle high pressure area which is cannibalizing your draft. I think going higher with the chimney should help :D
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut Size / White Ash

Re: Harmon MKII Backdrafting

PostBy: tmckenzie On: Mon Oct 29, 2012 6:39 am

I would try adding a section to the top of the flue and I bet it stops. I would take the cap off too. Somebody above drew a picture of the wind coming over your roof and right into it. I would bet money that is what is going on. And I also agree with the old farmer sense, if it is built for 6 inch, better use 6 inch.
tmckenzie
 
Stove/Furnace Make: saey
Stove/Furnace Model: 92

Re: Harmon MKII Backdrafting

PostBy: Bootstrap On: Mon Oct 29, 2012 7:19 am

Increase the hight of the chimney. Because the opening is where it is, when the wind blows its shoving air into the chimney. Get the top above that windy zone and your problem should go away. A 6" chimney shouldnt be needed.
Bootstrap
 
Stove/Furnace Make: Hitzer
Stove/Furnace Model: 30-95

Re: Harmon MKII Backdrafting

PostBy: Rex On: Mon Oct 29, 2012 8:44 pm

Id try pulling off a section of 8 inch pipe causing the chimney cap lower than the peak of your house. This should get your cap below the "jet stream" when the wind blows from the west. When you have a light snow and heavy western winds, watch the snow blow over the top of your house. The blowing snow will show the jet stream coming off the top edge of your roof, betting right on top of your cap. Lowering the chimney cap will place in a more neutral wind flow.

Be a cheap try...
Rex
 
Stove/Furnace Make: D.S. Machine
Stove/Furnace Model: Circulator 1500

Re: Harmon MKII Backdrafting

PostBy: Berlin On: Mon Oct 29, 2012 9:17 pm

Do NOT go to a 6" pipe. With subbit coal the installation is correct - you should change from 6"to 8" immediately after the stove collar. The 6" collar isn't an engineering decision it's a marketing one from stove mfg'rs - 6" is less expensive and more common, so people are more likely to buy a stove w/ a six inch collar for better or worse. What you do need, as was mentioned by a few posters, is to extend your stack higher - you have a very steep roof pitch and that will cause problems when a stack is of mediocre height compared to the peak. You need to add probably about 4' of stack height to deal with your problem and ditch the "H" cap it will cause you more problems than it will fix - go with a simple cap that's as open and free-flowing as possible.
Berlin
 
Hot Air Coal Stoker Furnace: Will-Burt Combustioneer 77B
Coal Size/Type: Ohio BITUMINOUS pea stoker coal

Re: Harmon MKII Backdrafting

PostBy: freetown fred On: Mon Oct 29, 2012 9:21 pm

Now there's something I'd try before panicking :) Nice Rex-- Nothing ventured, nothing gained--economic & hopefully efficient--you've got time to get this straightened out before hard winter sets in--it's not just this storm you need to be concerned with--on the other hand, BERLIN burns bit--you've got a head full of ideas here--keep us posted on your progress/ solution
freetown fred
 
Hand Fed Coal Stove: HITZER 50-93
Coal Size/Type: BLASCHAK Nut/Stove mix

Re: Harmon MKII Backdrafting

PostBy: Bootstrap On: Thu Nov 01, 2012 9:50 am

You will regret lowering the chimney. The height needs to clear the peak especially in A frames. It needs to do that or your stove will be fighting your house pressure. Essentially if your roof its higher, you could say its a more appealing chimney than your actual chimney...... That's chimney 101 stuff.
Bootstrap
 
Stove/Furnace Make: Hitzer
Stove/Furnace Model: 30-95

Re: Harmon MKII Backdrafting

PostBy: Yanche On: Thu Nov 01, 2012 12:50 pm

I would try to make some measurements. If you have a manometer, take a long stick longer than the height of roof, tape a plastic tube to it, something like the tube patients with oxygen machines or C-pap masks. Connect the ground end to you manometer and move the pole around and see what variation you get. The object is to measure the differential air pressure at the open top end of the tube with respect to the ground. Perhaps it will give you an idea how your roof changes the pressure. Try it with several wind conditions at various heights. I've never done this but it principle it should work.

Another measurement idea would be a smoke generator held up on a stick. Both ideas are to understand how you roof and unique wind directions affects your chimney draft.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: Harmon MKII Backdrafting

PostBy: coalcracker On: Sun Dec 08, 2013 1:22 pm

doctorclean wrote:Hello Gentlemen,

I hope you can give me some advice on my Harmon MKII setup. . I do have a manual damper and no manometer at this time.



did you ever get this sorted out ? a few thoughts...

nix the manual damper, Harman actually specifically states not to use one on their new stoves. Next time it backdrafts open the damper wide open, see if it stops. If you have a Mk. II it may be the top outlet stove ? I believe all the Harmon free standing stoves went to rear pipe outlets, but I'd have to check their product line to be sure.

one definite, change the chimney cap- get the type that has a separate band between the top and bottom, those are specifically designed to increase draft upwards no matter what direction the wind is from. See below, it's called a "windcap". I'm using one on my Harman Mk I and it never backdrafts, ever- even though the huge oak and maple trees around my home are quite close and tower over the chimney and house by at least 20 feet.

Image


A chimney with no cap is the most vulnerable to the adverse effects of wind. A cap, particularly one that has baffles to prevent direct line of sight access to the opening (as opposed to a simple flat rain cap) provides significant protection from the adverse effects of wind. In fact, research has shown that caps with baffles (of the sort common on factory-built chimneys) can actually enhance draft regardless of wind direction.
This kind of cap can take adverse winds and convert them to upward flow in the chimney.The cap shown at right is the type of design common on factory-built
chimneys. Note that the baffle, in the form of a band between the cap and the skirt at the base of the cap, prevents direct access of the wind to the open top of the chimney. This simple design consistently produces a driving pressure at the top of the chimney, regardless of wind direction or speed.
Adverse pressure can also occur when the top of the chimney is in a positive pressure zone caused by the velocity pressure of the wind as it flows against a raised part of the building behind the chimney (below). This is one case in which adding to the height of the chimney may help to resolve a wind-related venting problem.


next issue, you have the classic pressure differential problem created by when a rooftop is over and near a lower chimney, see below, someone else pointed this out earlier with red arrows showing airflow downward into chimney

Image

For example, wind can often flow down towards the top of a chimney after passing over an obstacle like a roof, adjacent building or trees. Wind may also approach the top of a chimney from below after flowing up a roofline to a chimney penetrating the peak. Wind tunnel testing has demonstrated that wind flowing from either above or below the chimney top can be adverse to upward flow by creating positive pressure at the top of the chimney.

Note that the thick black line in this and the other house drawings on this page is the building envelope, which contains the insulation and vapor barrier that encloses the warm spaces of the house.


and you also have a variation of this related problem, pressure zone created by the lower chimney next to higher rooftop

Image

Adding height to this chimney could get its top above the positive pressure zone and also make it higher than the second floor ceiling.
coalcracker
 
Hand Fed Coal Boiler: Standard sealed hot water boiler, hand fed
Hand Fed Coal Stove: Harman Mark I Magnafire
Baseburners & Antiques: Lehigh Oak 18, Washington potbelly, Sears Roebuck parlor cabinet, PIttston 6 lid cook stove, vintage combo gas/coal cook stove 4 lid
Coal Size/Type: nut
Stove/Furnace Make: Harman
Stove/Furnace Model: Mark I Magnafire

Visit Hitzer Stoves