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Old 12-23-2009, 11:48 AM   #1
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


I recently installed both a Vented Bathroom Fan and a Vented Range Hood in a Home I purchased last summer. All was well until winter hit.
The house has Vaulted Ceilings with little or no attic space to work in so I had to cut my way through the roof to do the install. Both Ducts have minimal runs in the attic, Bathrm = 18 inches, Range Hood = 6 inches.The Bathroom Fan has 2 backdraft dampers, one on the Fan Housing and one on the gooseneck on the roof. The Range Hood has only the one above the fan itself, no backdraft flap in the gooseneck on the roof.
Both fans have excessive cold air entering into the house. The outside temp is now -20c to -35c. Every morning there is ice on the metal parts inside the house. To start the day I have to remove the filters from the range hood and run the fan. This causes the condensation frozen in the duct to melt, dripping on the Ice Cold Glass Range Top below it. I understand it is due to condensation on the duct, and the extreme cold outside. I need to stop the cold air from entering the roof vents and dropping into the house.
While researching these projects I was amazed that there was not a positive backdraft stopper for sale or mentioned anywhere. The roof goosenecks are poor quality and all that is for sale locally, I am surprised that better products were not available in this northern climate. I knew condensation may be a problem but the cold air rushing into my home from both locations must be stopped.
Can anyone recommend a product or procedure that may solve my problem?

Update: Made a flapper for the Range Hood gooseneck. This has slowed the cold air invasion. Proper repairs will have to wait for better weather.


Last edited by Passion4Heels; 12-23-2009 at 05:21 PM. Reason: Updated information
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Old 12-23-2009, 06:29 PM   #2
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


You have a negative pressure in your house and I know all the symptoms, having lived in the Great White North all my life. Before you added the fans the air leaked in around your doors and windows etc. Easier to go thru the fans now. I had the same problems living in 3 story condos. How old is the house? You may need to have a combustion air pipe installed in your furnace room to break the negative pressure/equalize the house. I also lived in Calgary and ol Ralph was my MLA when sober.

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Old 12-23-2009, 08:43 PM   #3
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


The house was built in 1968.
The Furnace does not have a cold air intake near it. When I first bought the house the dryer vent was an accordion hose squished behind the drywall. I put in a hard pipe inside the room and vented through the old wall vent. Now the new hard pipe is usually full of cold air from outside and covered in frost behind the dryer. This is within 12 feet of the Furnace. The Furnace room has 2 doorways, both with curtains for doors. When the Furnace is running the curtains are drawn inwards slightly, I can see the draw. This would also be drawing in the cold air into the dryer duct, and the Bath and Range Hood upstairs.
There were many 'leaks' around this house. I changed weatherstripping, new back door, I have put poly on the inside of several of the windows trying to get things sealed up. Sounds like this might have actually made things worse.

Do I understand you correctly in saying I should add a cold air intake duct to the furnace room?
I like the theory. If I add the Cold Air Intake the pressure in the house should equalize and less cold air will be drawn in through the places it shouldn't.
Is there a recommended way for it to be done? Size? Length? I have seen the formula for figuring it out, it seems excessively complicated. If I was to add a cold air intake I would imagine of any size it would be an improvement to what has been for 40 years. A 4" hole is easier to make in the concrete foundation wall than a 6" one.

The flapper in the Range Hood gooseneck has made an amazing difference.

Last edited by Passion4Heels; 12-24-2009 at 04:30 PM. Reason: added details
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Old 12-24-2009, 04:02 PM   #4
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


You should have a 5 or 6" combustion air pipe installed from outside and dropped down to within a foot of the furnace at the floor. Depends on how many BTUs your furnace is firing (info inside furnace and whether you have a gas water heater). We usually make a trap/gooseneck on the pipe like a sink trap. Do you have an old fireplace in the house? There must be a reason you have such a severe negative pressure. You should have an energy audit done on the house and I would pay the fee and get an infrared scan done of the house. Houses of that era have 2x4 walls and poor vapor barrier and settling or poor installation of the fibreglass insulation. An infrared scan will show you all the heat leaks. An energy audit with a blower door/pressure test will show all the air leaks. Well worth the $$. The infrared would be best done now as the effect will be greatest (more difference between inside and out door temp equal better imaging). The other one I would do in the warmer weather. There is some kind of EcoEnergy federal program to help with those and give you info on grants for improvements.

Last edited by yuri; 12-24-2009 at 04:05 PM.
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Old 12-24-2009, 05:22 PM   #5
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


Yes there is a wood burning Fireplace. There were once 3 of them.
It's not just the Furnace and Water Htr. I have to be concerned about, The Dryer is also Gas.

If I add a 4" intake through the wall (you say 5 or 6" but I want to hear 4"), and run an insulated flex duct along the ceiling 12' and drop 7' the hose will be between the Furnace and Water Htr. I could then add a 5 gallon pail to stop the siphoning.
I expect this will equalize the pressure inside the house and should also decrease the drafts I have been trying to stop.

I don't think the scan will be necessary, I have found many of the leaks myself and have been working towards sealing them up. I agree the vapor barrier is probably poor but have no intention of gutting the drywall to fix it. If I can reduce the draw of cold air in the drafty spots I will be well ahead of the game.
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Old 12-24-2009, 05:49 PM   #6
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


THE fireplace(s) are the problem! There is air rising thru them and creating your negative pressure. Have them all sealed off properly and or get them replaced with an airtight type.Wood fireplaces are nothing but trouble in our climate. LOTS of updraft/chimney effect because of the huge difference between indoor/outdoor temps in our climate. Crack a window open slightly in the basement is what people used to have to do when they burned wood. 99% of them in Wpg. have been replaced and most people use direct vent gas fireplaces. Merry Xmas.
ps: It is -5 in Wpg and some fresh snow. Beautiful. Hope it is better where you are.
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Old 12-25-2009, 12:00 PM   #7
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


Yes Yuri, Merry Christmas. -15 here with a foot of fresh snow.

Two of the Fireplaces are already gone and sealed, the last is staying. It is a major feature of the house and one of the reasons we bought it. It has glass doors and a venting panel that all can be closed when not in use. This and the Flue Damper are enough to stop the chimney effect when not in use. When it is in use I do notice an increase in the downdraft through both fans, it all makes sense now with your advice.

Adding the flapper to the Range Hood Gooseneck has made an enormous difference. It is my hope that by coring a 4" hole through the concrete and adding an insulated duct to bring fresh air to the furnace and water htr. (and vicinity of the dryer) I will also be slowing down the cold air rushing in through the other cracks and voids around the house.
My original theory was to seal everything up as tight as I could get it to keep the heat in. Now with enough knowledge to be dangerous I can direct the influx of cold air to where it is needed and slow the draw of cold through the windows, doors and electrical outlets. All this and we don't get asphyxiated either, win win.

In speaking with a friend about his combustion air inlet, he has a 4" hose much like the one I intend to add. His has some cold air entering the home at all times, but when the furnace comes on it blows like it has a fan in it. I am hoping that 4" will do as the demand (low inside pressure) will draw additional volume when required.

Thanks for all your help/advice.
Merry Christmas and Happy New Year.
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Old 12-25-2009, 12:37 PM   #8
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


4" is TOO small and a waste of time IMO. Put a 5" in and a damper and throttle it if you want. I figured that you sealed a lot of leaks and the draft is looking for the easiest place to come in and that is the fans and dryer. After 31 yrs of this biz I have seen a lot of these scenarios. Going out to get stuffed this afternoon and back on the treadmill tomorrow. Let me/us know if you want more info and how it turns out.

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Old 12-25-2009, 01:14 PM   #9
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


"4" is TOO small and a waste of time IMO."

Those are the words I was afraid to hear. I will have to rent either size equip. to make the hole, just seems less of a big deal to cut 4" than 5 (structurally). I will have to have a good look at the area I intend to put it before I do any cutting. 5" it shall be.
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Old 08-19-2010, 04:56 PM   #10
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


OK... so I finally bit the bullet and hired a co. to core the holes for both the Combustion Air 5" and the Cold Air Return 4". They did a great job, quickly and with minimal mess. After reading about renting the gear and being charged for the wear on the bits and all I decided hiring someone was the way to go. There went $600.
So now I'm trying to insert the Galvanized Intakes into them and guess what, they don't fit. I guess I should have asked for 5 1/4" & 4 1/4" holes and filled the perimeter with spray foam once they were installed. Hindsight = 20/20.
I tried wetting the ID of the hole, no help. Then I greased em up with vasoline, that just made a mess. I cant tap them in with a persuader due to the hood on the ends.
Right now I have the intakes in the freezer trying to shrink them down enough to fit. There must be a better way.
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Old 08-19-2010, 05:59 PM   #11
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


Try your method first. If it fails I have one but it involves sheet metal snips and some creativity.
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Old 08-19-2010, 06:39 PM   #12
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


I think I'd cut and crimp them.
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Old 08-19-2010, 06:41 PM   #13
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


I thought that sounded too easy, it didn't gain me anything.
They both go in about 3". The 5" has a spot welded seam, the 4" is a crimped seam.
I expect the way to go is to cut a new 'seam' longitudinally, thus allowing the pipe to collapse a bit. Once it is in the hole I can 'foil tape' the cut from the inside of the pipe.
Cut the top, bottom or side? Does it matter?
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Old 08-19-2010, 07:00 PM   #14
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Backdraft, Cold Air and Ice from Range Hood and Bath Fan


My Goodness, a psychic Canadian Eh. Exactly what I was going to suggest. Cut it at the top so no condensation leaks out the joint. A roll of silver tape and tube of silicone is a work of art in the hands of a master tradesperson.

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