Confused on the Harman venting

That is strange. I thought an elbow was 5.

I am unsure if the 4" versus 3" pipe makes a difference on calculations but I would see if the vent manufacturer has better directions. Most stove install directions I've seen have stated to follow the pipe manufacturer's directions, and then just give you generalities. Sorry I'm not more help!

Each foot of horizontal pipe equals 1 lineal foot. You want to keep horizontal runs as short as possible. So if you have 3 ft. of horizontal it counts as three feet. Elbows and T's count as more lineal feet since they restrict the flow to a degree.

Vertical pipe counts 1 ft. per lineal feet. SO if you have a 5 ft. rise that counts as 5 feet also.

So say you have 3 ft. horizontal (= 3 ft) plus a horizontal T (= 5 ft) plus the vertical riser of 5 ft. Thus, 3 + 5 + 5 = 13 lineal feet if using 4" vent per Harman install manual.

Now if the T is vertical it counts as 2.5 ft. So this formula would be 3 + 2.5 + 5 = 11.5 lineal feet with 4" vent.

3" T's = 4 feet.

Here is the chart I am reading: From my P68 install manual.

*** This is for 4 inch***

Vertical 90* or T: 2.5'
Vertical 45* 1.5'
Horizontal 90* or T 5.0'
Horizontal 45* 2.5'

Note: 3" is different but spelled out as well.

Horizontal runs penalize you or count as more. Hope this explains it.

Vertical runs are 0.5 per 1 foot of vertical pipe.

Horizontal runs are 1.0 per 1 foot of horizontal pipe, and that pipe had better not be on bubble, it must have 1/4" rise per foot.

EVL calculations are independent of pipe size what changes is the maximum EVL before changing the pipe size.

15 is the maximum EVL for reliable operation with 3" pipe and is the switch over point to 4" pipe, going from that to a 6" circular flue and things get dicey.

And yes, there is a limit because after the pipe gets so big the weight of the air in the vent stack becomes too much for the exhaust blower to overcome.

Well hell.... I learned something. I probably could have barely gotten by with 3" but ran 4" to be sure. Is the 3" vertical .5 per foot or 1 per foot Smokey?

I found this to be very handy .......

Change the file extender .txt to .xlsx and use it in Excel.

bags said:

Well hell.... I learned something. I probably could have barely gotten by with 3" but ran 4" to be sure. Is the 3" vertical .5 per foot or 1 per foot Smokey?

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and

LuvMyPellets said:

Thanks Smokey that makes more sense. What had me totally screwed up is Harmans example given in the manual. They Give 20 for 3 inch and 30 for 4inch yet when they give an example for 3" They list 8 Ft vertical- 1-90 vertical and 4Ft of Horizontal snd you assume that adds up to 20. For 4 inch it is 12 ft Vertical- 1-90 Vertical and 4ft horizontal which supposedly adds up to 30. They give no subtraction values for straight pipe but they list all the subtraction values for elbows and tees. You stated 1.0 for Horiz and .5 for vertical 1ft length for 3inch. I am assuming they are a little higher for 4"?

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Vertical vent has an EVL of 0.5 that is 1/2 per foot of vertical vent.

The EVL cut offs are dependent on altitude and the ability of the exhaust blower to move air. Harman has two paddle arrangements on the exhaust blowers they are known as single and double paddles.

But EVL itself is independant of vent size and is calculated based on the bend angle and orientation of the venting. All venting sections need a rise in them of at least 1/4 " per foot of horizontal distance.

So that example is 8 feet vertical = 4 EVL, 90 degree bend = 5 EVL , plus 4 feet horizontal = 4 EVL adding up to 13 EVL which unless you are high on a mountain somewhere is fine for 3" vent.

Some stoves with less ump in the exhaust blowers may have cutoffs at different EVLs but the EVL calculations do not depend on vent diameter.

Yeah, Thanks for the clarification. The manuals are somewhat vague to say the least. I did know that you should limit horizontal runs and were penalized but I did not know that it was reversed in a sense where you cut it to half or .5 for the vertical per foot and that is how the difference is made up.

I get it now an hopefully I didn't add confusion. Also sorry if I did. Smokey owns the venting dept.!

I've not seen where it's ever been mentioned that it matters if the vent is inside or outside. I have to believe it matters since the guys burning wood stoves which require natural draft are investing a great deal of $ in insulated liners. Is it possible to assume that an interior vertical is 1/2 per foot and an external is 1 per foot?

Johninwi,
See what Smokey thinks. He's the go to guy on the venting. I haven't a clue on the in / out vertical calc's since my wood insert and free standing are tied into existing chimneys. I do know you need the flue or pipe to heat up to pull the smoke out. I try to be helpful because I have gained so much here but I still have some learning to do.

All stand alone pellet stove venting is technically of the insulated type although not as insulated as some cord wood burning flues I've seen.

The reason for the insulation attached to those natural draft devices is three fold, to help start the draft via the heated exhaust, to stop the bad things from condensing (precipitating out according to some folks) in the flue, and to decrease clearance to combustibles.

EVL is a measure of air flow resistance that the exhaust fan has to overcome.

EVL is not a factor for the natural drafters, it is for the forced beasts.

The amount of insulation needed for the forced beast isn't as much as that needed for the natural drafters.

The forced beasts burn cleaner on all settings than the natural draft units.

Now once again EVL does not vary by the vent cross section (3", 4", .....). It is strictly length and orientation.

I am not now, nor have I ever been a venting guru. Funny things happen in gas flow systems so several things have to be taken into consideration.

Oh have I mentioned never vent in to the prevailing wind?

Appreciated, thankyou. Failed to considered the double wall and air gap, air being a good insulator.

SmokeyTheBear said:

I am not now, nor have I ever been a venting guru.

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is resident expert acceptable?

johninwi said:

Appreciated, thankyou. Failed to considered the double wall and air gap, air being a good insulator.



is resident expert acceptable?

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Not even close. Just a critter who has done a lot of reading. I know there are some venting folks on here that handle things more in getting hot air from here to there on a regular basis but clean heated air or dirty exhaust air the mechanics are the same.