Negative pressure brain teaser

[dskup]

A train leaves point A and heads southeast at 100 mph. Another train leaves point B heading... oh wait. Wrong brain teaser.

I have two wood burning appliances, a Fisher stove in the basement and a Quad fireplace on the first floor. The Fisher has a 4'x4' copper hood above it with an 8" duct and inline fan that pushes air up to the first floor. The Quad has a blower, the intake of which is ducted to the basement via a 2.5 by 12.

When I run only the Fisher all day it creates such a negative pressure that is literally sucks my basement door closed. When I only run the Quad all day, there's no noticeable negative pressure. Why is this? The Quad has a much more powerful blower.

Considering there is a 10" fresh air intake in the basement, I'm amazed that a negative pressure can be created at all!

 

[LLigetfa]

Regardless of the fresh air intake, if you pressurize the upstairs, it is the pressure upstairs that is closing the door, not necessarily the vacuum downstairs. A negative pressure in the basement is negative compared to the higher pressure upstairs. Moving air is like moving electricity. You need to complete the circuit.

You claim the Quad has a more powerful blower but the Fischer may have natural convection on its side.

 

[oconnor]

The Fisher is already below the neutral pressure plane in your house, so it has a head start on the Quad.

When you run your Fisher, you have three sources of depressurization - chimney draft, copper hood with fan, and stack effect.

Given the head start, no doubt it is sucking the door shut.

As for the hot air hood -BAD PLAN- you will eventually get a cold enough flue going that you can reverse the flow on the Fisher, especially if you already have enough air leaving the basement to slam a door shut. I have done it to myself, so I'm not talking about the theoretical. It sucks (pardon the pun).

He is the full story https://www.hearth.com/econtent/index.php/forums/viewreply/287928/

Any kind of forced air hood moving heat away from the stove is way against code, and will eventually cause the laws of physics to smoke you out.

 

[Hogwildz]

Not to mention that fisher prolly has a 8" stack, as compared to the Quad's 6"? Fisher has more draft and no secondary, so more flowing into the Fisher and out the stack, then the Quad.

 

[fossil]

Dunno 'bout the pressure differentials you're experiencing, but I will say simply that where I live, that copper hood w/fan over the top of the basement stove would be a violation of mechanical code. Perhaps it's different where you live. Rick

 

[dskup]

Wow. I learned more in four posts than I did in four years of college... and I'm not joking!

I had no idea that the hood is against code. It was there when I bought the house. My chimney sweep did an initial inspection the first time he cleaned, and he identified six code violations- none of which were the hood. The one he was most conserned about is the two 90 degree elbows in the 8" pipes leading to the chimney. He also said the clay flue is way oversized. BUT... I burned the Fisher for many years before getting the Quad on the main level, and it did me proud. The chimney is 40' high, so the draw is monsterous as you might imagine.

But the room that the Fisher is in is small, and is covered in very old varnished knotty pine. I started to feel as though it was a distaster waiting to happen. And thus, the unit upstairs.

 

[mnowaczyk]

Wow. I learned more in four posts than I did in four years of college... and I'm not joking!

I had no idea that the hood is against code. It was there when I bought the house. My chimney sweep did an initial inspection the first time he cleaned, and he identified six code violations- none of which were the hood. The one he was most conserned about is the two 90 degree elbows in the 8" pipes leading to the chimney. He also said the clay flue is way oversized. BUT... I burned the Fisher for many years before getting the Quad on the main level, and it did me proud. The chimney is 40' high, so the draw is monsterous as you might imagine.

But the room that the Fisher is in is small, and is covered in very old varnished knotty pine. I started to feel as though it was a distaster waiting to happen. And thus, the unit upstairs.

What size is your clay liner? Did you line your chimney?

(Designing a system now and looking for experiences.)

Thanks,
Mike