:grin2: Long time lurker, first time poster! Appreciate the community here :grin2:
TL;DR:
- What I’m trying to solve: Negative home air pressure. Wood stove / fireplace flue is backdrafting causing smoke smells into the home
- Question: Is there an active make up air system that senses a home's air pressure and can actively bring in outside filtered air to keep home under neutral air pressure?
Background:
With my wood stove flue shut (as much as it can, it is metal so obviously not sealed completely), it still pulls air down the flue when one of my bathroom vents is on.
When all my bathroom exhaust vents are on and my kitchen vent is on, the air is rushing down the flue.
I guess the least path of resistance, even with the flue closed, is the flue...
I recently had my HVAC duct work replaced entirely as leaks on the supply side were placing the house under negative pressure. However, now the ducts have < 3% leakage and if I open the flue with only the HVAC running (no exhaust fans running) there is no backdraft.
So it seems now the only backdraft occurs when at least one of the following is running: one of the bathroom exhaust fans or the kitchen exhaust fan
I was told by the company that performed my blower door test is that I have a relatively tight home as compared to other homes in similar age. The crawl space is sealed and the ceiling around the fixtures are sealed.
I have done some simple testing by cracking an exterior door slightly:
Also, with the door or window cracked, there is no backdraft down the flue anymore!
I understand through reading this forum and several other resources that I need makeup air.
What is the best approach in supplying make up air?:
Are there any other options I’m missing or other recommendations?
Is there a system that has a pressure sensor where it “senses” my homes air pressure and can actively bring in outside air as needed to keep home neutral?
It seems crazy to me that every time I think about this problem, the solution is to bring in outside air… but then I stop an think about it and right now my wood stove flue is supplying my make up air… but dirty smelly air...
Appreciate any advice and thoughts! :cheers:
Data of my home to help with recommendations:
TL;DR:
- What I’m trying to solve: Negative home air pressure. Wood stove / fireplace flue is backdrafting causing smoke smells into the home
- Question: Is there an active make up air system that senses a home's air pressure and can actively bring in outside filtered air to keep home under neutral air pressure?
Background:
With my wood stove flue shut (as much as it can, it is metal so obviously not sealed completely), it still pulls air down the flue when one of my bathroom vents is on.
When all my bathroom exhaust vents are on and my kitchen vent is on, the air is rushing down the flue.
I guess the least path of resistance, even with the flue closed, is the flue...
I recently had my HVAC duct work replaced entirely as leaks on the supply side were placing the house under negative pressure. However, now the ducts have < 3% leakage and if I open the flue with only the HVAC running (no exhaust fans running) there is no backdraft.
So it seems now the only backdraft occurs when at least one of the following is running: one of the bathroom exhaust fans or the kitchen exhaust fan
I was told by the company that performed my blower door test is that I have a relatively tight home as compared to other homes in similar age. The crawl space is sealed and the ceiling around the fixtures are sealed.
I have done some simple testing by cracking an exterior door slightly:
- with no exhaust fans running: there is no air moving thru the crack (in or out)
- with only the HVAC running: there is no air moving thru the crack (in or out)
- with the 50 CFM bathroom fan running: there is a good amount of air moving from outside to inside
- with both the 50 CFM and 110 CFM bathroom fans running: there is a very good amount of air moving from outside to inside
- with both bathroom fans and kitchen exhaust fans running: there is an amazing amount of air moving from outside to inside
Also, with the door or window cracked, there is no backdraft down the flue anymore!
I understand through reading this forum and several other resources that I need makeup air.
What is the best approach in supplying make up air?:
- Fresh make up air supply (filtered) ducted to the return side of HVAC: My understanding is this really only helps when the HVAC is running or no? I don’t have a negative air pressure issue with the HVAC running so I’m feeling this won’t fix the issue or is that incorrect? I have heard having a fresh air supply on the HVAC return can actually place the home under positive pressure that can cause other issues.
- Active fresh make up air supply: A duct from outside to inside, with a filter and damper, that pulls in the same amount of air being exhausted to keep home neutral.
Are there any other options I’m missing or other recommendations?
Is there a system that has a pressure sensor where it “senses” my homes air pressure and can actively bring in outside air as needed to keep home neutral?
It seems crazy to me that every time I think about this problem, the solution is to bring in outside air… but then I stop an think about it and right now my wood stove flue is supplying my make up air… but dirty smelly air...
Appreciate any advice and thoughts! :cheers:
Data of my home to help with recommendations:
- Ranch Home Built 1987
- 2,014 square foot, 3 bed, 2 bath
- Location: South East, IECC Climate Zone: 3, BA Climate Zone: Mixed-Humid, IECC Moisture Regime: A
- Encapsulated Crawl space: 20 mil vapor barrier, seam sealed up foundation walls to 6" of rim joist
- Radon Test: 1.7 ± 0.5 pCi/l
- New HVAC ducts installed in 2022 with < 3% leakage. All mastic sealed, including boots in crawl and up thru sub floor.
- MERV 13, 4” Filter on return before blower
- Bathroom exhaust vents 6" ducted & insulated out roof. Bathroom 1 is 50 CFM, Bathroom 2 is 110 CFM
- Kitchen exhaust vent, 6” ducted outside, 450 CFM
source https://hvac-talk.com/vbb/threads/2238876-Home-Make-Up-Fresh-Air-Supply?goto=newpost
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