Who can troubleshoot backdrafting/pressure issues in an air-tight home?
#1
11-26-15, 04:51 PM
Who can troubleshoot backdrafting/pressure issues in an air-tight home?
I've got two threads in different sections. I'm concerned about where I need to go from here from a safety standpoint since we're talking about carbon monoxide & ventilation & such.
Thread 1: Lot of dust in the house, where is it coming from & how do I get rid of it? (primary reason for joining forum)
Thread 2: Might need ductwork modification due to high pressure, how can I verify before performing renovations. (just wanted to verify the estimated expense)
I've learned:
1) Yes the ducts were under high pressure. I reduced the furnace fan speed & replaced the air filter from pleated to fiberglass to relieve pressure.
2) Ducts are not fully sealed (they are metal rectangular ducts, hidden by drywall).
3) That my house is probably air-tight because:
4) My water heater backdrafts whenever the bathroom fan is on. It's probably backdrafted every single morning.
5) Opening specific windows in the basement relieve the backdrafting of the water heater.
6) There was a lot of dust on a return-air duct that was right above the water heater.
7) My clothes dryer has humid air coming in around the vent where it goes through the wall when clothes are drying. This tells me the exhausted air is coming back into the house.
Some quick specs:
- 40 btu high efficiency furnace, dual PVC pipes for combustion
- 2 ton a/c
- 40 gal water heater, flue connected to a same-diameter metal chimney sleeve
- ducts are rectangular metal in the floor joists, 4"x8" duct to 2.5"x12" opening
Since unbalanced air pressures seems to be the underlying problem in this house, what do I do to fix it before it starts affecting my health? Or if anyone knows who I should specifically call who can come in & figure out my issues, that helps too. Someone who would do some serious troubleshooting/investigating.
Thank you.
Thread 1: Lot of dust in the house, where is it coming from & how do I get rid of it? (primary reason for joining forum)
Thread 2: Might need ductwork modification due to high pressure, how can I verify before performing renovations. (just wanted to verify the estimated expense)
I've learned:
1) Yes the ducts were under high pressure. I reduced the furnace fan speed & replaced the air filter from pleated to fiberglass to relieve pressure.
2) Ducts are not fully sealed (they are metal rectangular ducts, hidden by drywall).
3) That my house is probably air-tight because:
4) My water heater backdrafts whenever the bathroom fan is on. It's probably backdrafted every single morning.
5) Opening specific windows in the basement relieve the backdrafting of the water heater.
6) There was a lot of dust on a return-air duct that was right above the water heater.
7) My clothes dryer has humid air coming in around the vent where it goes through the wall when clothes are drying. This tells me the exhausted air is coming back into the house.
Some quick specs:
- 40 btu high efficiency furnace, dual PVC pipes for combustion
- 2 ton a/c
- 40 gal water heater, flue connected to a same-diameter metal chimney sleeve
- ducts are rectangular metal in the floor joists, 4"x8" duct to 2.5"x12" opening
Since unbalanced air pressures seems to be the underlying problem in this house, what do I do to fix it before it starts affecting my health? Or if anyone knows who I should specifically call who can come in & figure out my issues, that helps too. Someone who would do some serious troubleshooting/investigating.
Thank you.
#2
11-26-15, 05:08 PM
Group Moderator
1) Yes the ducts were under high pressure. I reduced the furnace fan speed & replaced the air filter from pleated to fiberglass to relieve pressure.
The ducts are normally under pressure when the system is running.
Unfortunately I'm not a duct man so I can't give you much help on that front. It does sound like you may need to add a fresh air vent to your furnace room for the hot water heater.
#3
11-26-15, 06:37 PM
Member
An energy audit firm with a blower door can certainly evaluate the tightness of the house and verify (or not) your observations of back drafting, etc. They can make recommendations for an HRV or outside air supply if appropriate to relieve any problems without having to leave a window open.
I don't think they'll be any help with the dust/furnace concerns though.
I don't think they'll be any help with the dust/furnace concerns though.
#4
11-26-15, 06:40 PM
Yep, the temperature rise was checked after adjusting fan speed. Went from a rise of 40 degrees to 55 degrees. Spec is 35-65.
Unfortunately I think there's just too many issues that now I'm just trying to find out what type of guy I need to get in here who would know how to hit all the angles. For example, even with make-up air, opening window "A" fixed the backdraft issue but opening window "Y" didn't...turns a simple solution into another investigation...
If a low-powered 60 cfm bathroom fan can make a water heater backdraft...that just feels like the tip of the iceberg and I need a pro to figure this out.
Unfortunately I think there's just too many issues that now I'm just trying to find out what type of guy I need to get in here who would know how to hit all the angles. For example, even with make-up air, opening window "A" fixed the backdraft issue but opening window "Y" didn't...turns a simple solution into another investigation...
If a low-powered 60 cfm bathroom fan can make a water heater backdraft...that just feels like the tip of the iceberg and I need a pro to figure this out.
#5
11-26-15, 07:20 PM
@jp "If a low-powered 60 cfm bathroom fan can make a water heater backdraft...that just feels like the tip of the iceberg and I need a pro to figure this out."
One of the gaps in the construction profession is between hvac pros and energy pros. I have yet to meet an hvac pro (here in Maine) that frequently checks worst case depressurization. They may check draft at time of service, but that is without other exhaust appliances operating. On the other side, an energy auditor can identify pressure problems but rarely would do a duct redesign.
Since very few homes are actually built to the extreme "tight" that would result in backdrafting, the first area i would be checking would be the air paths to be sure make-up air is available from a larger area then a small utility room. Even a basement can be too tight if isolated from the rest of the house. If you were to open every interior door and repeat your test it might provide different results.
Since your test wasn't run (if memory serves me) with the furnace fan running, then the pressures involved from a poorly balanced duct system should not be in play.
Before I forget, be sure your dryer vent is not obstructed, filled with lint.
If you want some related reading Google "worst case depressurization test"
Bud
One of the gaps in the construction profession is between hvac pros and energy pros. I have yet to meet an hvac pro (here in Maine) that frequently checks worst case depressurization. They may check draft at time of service, but that is without other exhaust appliances operating. On the other side, an energy auditor can identify pressure problems but rarely would do a duct redesign.
Since very few homes are actually built to the extreme "tight" that would result in backdrafting, the first area i would be checking would be the air paths to be sure make-up air is available from a larger area then a small utility room. Even a basement can be too tight if isolated from the rest of the house. If you were to open every interior door and repeat your test it might provide different results.
Since your test wasn't run (if memory serves me) with the furnace fan running, then the pressures involved from a poorly balanced duct system should not be in play.
Before I forget, be sure your dryer vent is not obstructed, filled with lint.
If you want some related reading Google "worst case depressurization test"
Bud
#6
11-27-15, 08:11 AM
Bud, the interesting thing is, opening the window in the furnace room to give it make-up air still resulted in backdrafting. All interior doors stay open in the house even in the basement.
Correct, the furnace fan was not on. Basically nothing was going on in the house except the bathroom fan being on & then running the hot water.
Dryer vent is clean. It's only a 2 foot run from the dryer to the brick, easy inspection & clothes dry fine.
I actually have a manometer that I bought for measuring the furnace. I think I can make use of it for doing that worst case depressurization test. Just need extra long lengths now. Probably compare different areas inside the house vs. outside the house to see if there's excessive pressure somewhere. Worst case for me would be bathroom fan + furnace + clothes dryer.
Correct, the furnace fan was not on. Basically nothing was going on in the house except the bathroom fan being on & then running the hot water.
Dryer vent is clean. It's only a 2 foot run from the dryer to the brick, easy inspection & clothes dry fine.
I actually have a manometer that I bought for measuring the furnace. I think I can make use of it for doing that worst case depressurization test. Just need extra long lengths now. Probably compare different areas inside the house vs. outside the house to see if there's excessive pressure somewhere. Worst case for me would be bathroom fan + furnace + clothes dryer.
#7
11-27-15, 09:03 AM
I don't recall if you told us which manometer you picked up, but does it read in Pascals or inches of water? A 1/4 inch water column equals about 60 pascals and the pressures we measure to determine draft or backdraft are less than 10 pascals.
The fact that one window stops the backdrafting and another at the same level is just an indication as to how marginal your situation is. Currently sitting right on the threshold.
A couple of details. That threshold is created by house stack effect where cold air leaks in the lower levels and forces the warm air up and out the upper levels. Depending upon the size and location of those leaks there will be a neutral zone somewhere in between. If there are more leaks high or low, then the pressure within the house adjusts to equalize the infiltration to match the exfiltration, always taking into account any appliance air flow. A gas water heater can spill with as little as 2 or 3 Pascals. Here is a reference, although I have not read this one I am familiar with the source.
Backdrafting Heating Equipment Hazards Guide
Here's an example: If you were to open your attic access a lot of house air would be escaping. To compensate for that the house pressure would decrease making the ceiling near the attic access less positive and the basement where your water heater is located more negative. The negative shift is attempting to increase the infiltration to match the now increased exfiltration. Searching for leaks, look up high. Recessed lights, that attic hatch, or even the gap around a plumbing vent that starts in the basement, it provides a point of exfiltration.
Another note. When the water heater is backdrafting it may not be getting the proper flow of combustion air and the resulting incomplete burn may be resulting in the fibers you are seeing, like the black soot you would see on the glass door of a fireplace. That incomplete burn can also be a source of CO.
Bud
The fact that one window stops the backdrafting and another at the same level is just an indication as to how marginal your situation is. Currently sitting right on the threshold.
A couple of details. That threshold is created by house stack effect where cold air leaks in the lower levels and forces the warm air up and out the upper levels. Depending upon the size and location of those leaks there will be a neutral zone somewhere in between. If there are more leaks high or low, then the pressure within the house adjusts to equalize the infiltration to match the exfiltration, always taking into account any appliance air flow. A gas water heater can spill with as little as 2 or 3 Pascals. Here is a reference, although I have not read this one I am familiar with the source.
Backdrafting Heating Equipment Hazards Guide
Here's an example: If you were to open your attic access a lot of house air would be escaping. To compensate for that the house pressure would decrease making the ceiling near the attic access less positive and the basement where your water heater is located more negative. The negative shift is attempting to increase the infiltration to match the now increased exfiltration. Searching for leaks, look up high. Recessed lights, that attic hatch, or even the gap around a plumbing vent that starts in the basement, it provides a point of exfiltration.
Another note. When the water heater is backdrafting it may not be getting the proper flow of combustion air and the resulting incomplete burn may be resulting in the fibers you are seeing, like the black soot you would see on the glass door of a fireplace. That incomplete burn can also be a source of CO.
Bud
#8
11-27-15, 11:27 AM
Manometer can supposedly read 0.01 inH2o resolution which'll equal about 3 Pascals. I doubt it's accurate though since it's very low end...so I guess I'm probably wasting my time if the pressures I'm dealing with are at the extreme low end of the instrument I'm working with.
I'm a little confused. It sounds like you said that opening the attic hatch relieves pressure in the main floor & therefore increases it in the basement? So that the more open the main floor is to the attic, the more air wants to come into the basement (because of stack effect)? And if more air wants to come into the basement the water heater's flue is an entry point (that the water heater burner ultimately loses against)?
So I guess opening a basement window (or another make-up air thing) has the same effect you describe of relieving the negative pressure in the basement then? And that helps restore the pressure in the basement so the water heater can draft ok?
Sorry for all the questions --- so does this mean my issue is too little pressure buildup on the main floor against the attic or not enough pressure relief in the basement? What happens if you fix one but not the other?
CarbideTip - yeah I think I'll have to look into the blower door to see how airtight it is. I just don't want it to stop there though. I don't want to be given a report with numbers - I need some "this is your issue" terminology & not recommendations. The fact that the dust is only on the air duct right above the water heater might be a clue though.
I'm a little confused. It sounds like you said that opening the attic hatch relieves pressure in the main floor & therefore increases it in the basement? So that the more open the main floor is to the attic, the more air wants to come into the basement (because of stack effect)? And if more air wants to come into the basement the water heater's flue is an entry point (that the water heater burner ultimately loses against)?
So I guess opening a basement window (or another make-up air thing) has the same effect you describe of relieving the negative pressure in the basement then? And that helps restore the pressure in the basement so the water heater can draft ok?
Sorry for all the questions --- so does this mean my issue is too little pressure buildup on the main floor against the attic or not enough pressure relief in the basement? What happens if you fix one but not the other?
CarbideTip - yeah I think I'll have to look into the blower door to see how airtight it is. I just don't want it to stop there though. I don't want to be given a report with numbers - I need some "this is your issue" terminology & not recommendations. The fact that the dust is only on the air duct right above the water heater might be a clue though.
