One 90 Elbow or Two 45's ?

[leeave96]

For my Englander install, I just need to come straight up and make a 90 degree turn into the chimney. What is your preference, one 90 elbow or two 45 degree elbows with a bit of separation between?

Just courious.

Thanks!
Bill

 

[rdust]

If chimney height is on the low side I would use 2 45's. I'm the same set up but with a 30' chimney the one 90 doesn't seem to cause any issues.

 

[jimbom]

1988 ASHRAE Equipment Handbook, Chapter 26 Chimneys,.... Systems, page 26.10, Table 9 Resistance-Loss Coefficients. (Showing my age :-S )

One Round Elbow 90, Loss Coefficient suggested design value 0.75
One Round Elbow 45, Loss Coefficient suggested design value 0.3

Total loss coefficient for a system including the stove might be in the range of 20 plus or minus 5 or so.

These are dimensionless numbers, so they work with any diameter chimney. Bottom line is 2 45s are about the same loss as one 90. On a percentage basis if the overall loss coefficient was 20, the system with 2 45s would be about 1% less restrictive to flue gas flow. I think it depends on how you want it to look rather than how it will perform.

 

[BrotherBart]

Two 45s win every day of the week.

 

[summit]

In theory, 2 45's works better. In reality, one 90 will probably do just as well.

 

[Backwoods Savage]

I've never used 2 45's but they should work better than a 90.

 

[oldspark]

In theory, 2 45's works better. In reality, one 90 will probably do just as well.

I thought it was the other way around, on paper 2 45's did not make that much difference but in reality most people thought it did.

 

[Wood Heat Stoves]

I would just use a 90. Draft won't be any different, but it's simpler with fewer joints.

 

[leeave96]

With two 90's, I'm thinking a bit better flow, but mostly I think it would look better - we'll see.

One thing I am going to try is some welded vs snap together stove pipe. Anyone know of a vendor that sells a smooth 45 or 90 degree elbow? I'm thinking that if it is smooth, there is one less thing to grab creosote that may make it's way through the stove.

Thanks!
Bill

 

[begreen]

If draft is marginal then using a 45 + short connector + a second 45 can make a difference. We have seen it here several times. Marginal draft frequently happens with shorter flues during the shoulder season. Using double wall pipe in this case will also help draft by keeping the flue gases hotter.

Here's a link to shots of how we set up a yurt installation that has a 12' stack. There are 2 45's on the Morso.

https://www.hearth.com/talk/threads/27154/

 

[Fsappo]

2 45's look horrid and give you more "stuff" I'd go with the 90 and fall back to the 2 45's if your draft is lacking and you already tried everything else to fix it. Now if it was me, and I didnt care what it looked like, I would go with 2 45s...just because of the slight chance it "may" show a noticable difference. But I also put That awesome "More than Mustard" from Oscars in Warrensburg, NY on my pizza. So go figure

 

[begreen]

I have to disagree with the "looks" issue. One gets used to the look very quickly. We have a 2-45 offset that was necessary to connect the T6 where the Castine was installed and hardly notice it now.

 

[Backwoods Savage]

BeGreen has a point. You do get used to the look quite fast. Some don't even like the looks of stove pipe in the house but to me it is just part of the stove and does not look bad at all. Well, maybe back when people did not use black pipe it could look bad.

 

[rdust]

I'm well past caring what it looks like, all I want it to do now is heat my house when it's zero outside.

 

[BrotherBart]

I'm well past caring what it looks like, all I want it to do now is heat my house when it's zero outside.

Arrived there myself about 1985. And yes, it does do zero here sometimes. Just not for weeks on end. Did that, I would move.

The 45s are more efficient. You cannot repeal the laws of fluid dynamics. Whether it is air with smoke in it or liquids. It is all about friction.

 

[begreen]

Sometimes there is beauty in function over form.

 

[Todd]

With two 90's, I'm thinking a bit better flow, but mostly I think it would look better - we'll see.

One thing I am going to try is some welded vs snap together stove pipe. Anyone know of a vendor that sells a smooth 45 or 90 degree elbow? I'm thinking that if it is smooth, there is one less thing to grab creosote that may make it's way through the stove.

Thanks!
Bill

Try www.woodlanddirect.com

 

[Backwoods Savage]

I'm well past caring what it looks like, all I want it to do now is heat my house when it's zero outside.

Now that is pure wisdom!

 

[Dirtsurgeon]

How much further will 2- 45's kick the stove out into the room? 3 or 4 inches?

Thanks,
Dirt

 

[begreen]

It depends on the setup and length of the horiz. section of the connector. Sometimes it doesn't move the stove out into the room any more than going straight up to a 90 and then to a connector.