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Old 09-25-2012, 12:53 AM   #16
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Where to attach Fresh Air intake location on return plenum


RE Combustion air..If you can pull your washing machine out from the wall a little then you can tuck the combustion air down behind. Just let it hang down behind and then loop end back upwards to form a j at the bottom. This will allow air to be drawn in when needed and prevent excess cold air from entering when furnace is not running. Also you can flatten the flex duct a bit. As long as you don't crush/collapse it ..it will still allow the same amount of air intake as if it were perfectly round. AND JUST A FURTHER NOTE If you can leave the door to the laundry room open to the rest of the house OR put an air grill in the door you are not required to provide outside combustion air so you could eliminate it. Particularly since you are bringing fresh air into the house via the return air, as long as you have 144 sq inch free opening from laundry room to main area of house you will have enough combustion air from within thereby you can eliminate the outside combustion air intake.
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Old 09-25-2012, 04:12 AM   #17
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Where to attach Fresh Air intake location on return plenum


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RE Combustion air..If you can pull your washing machine out from the wall a little then you can tuck the combustion air down behind. Just let it hang down behind and then loop end back upwards to form a j at the bottom. This will allow air to be drawn in when needed and prevent excess cold air from entering when furnace is not running. Also you can flatten the flex duct a bit. As long as you don't crush/collapse it ..it will still allow the same amount of air intake as if it were perfectly round. AND JUST A FURTHER NOTE If you can leave the door to the laundry room open to the rest of the house OR put an air grill in the door you are not required to provide outside combustion air so you could eliminate it. Particularly since you are bringing fresh air into the house via the return air, as long as you have 144 sq inch free opening from laundry room to main area of house you will have enough combustion air from within thereby you can eliminate the outside combustion air intake.
Doing that will tend to lower the indoor RH in winter.
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Old 09-25-2012, 09:54 AM   #18
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Where to attach Fresh Air intake location on return plenum


Been There....Really? RH is lowered when you increase air temperature therefore when you introduce more outside air when it is cold, when it warms up, the RH will decrease. However, if you cut off outside air and retain the air within the house, once everything is warmed up to "room temp" the RH will only vary according to the introduction and amount of outside air, where it will reduce the RH, once it is warmed up...... OR...introduction of more water vapor, from showers, kettle, humidifier etc., so, the RH will increase.

Six of one ..half a dozen of the other..as far as I'm concerned. Also depends if the house is air tight or not..too much humidity = possible mold...too little humidity then you require a humidifier and you may have too many air leaks costing more in energy.and so on and so on


In other words...cutting off fresh air intake will increase RH.
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Old 09-25-2012, 11:19 AM   #19
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Where to attach Fresh Air intake location on return plenum


Taking combustion air from the occupied/living areas of a home lowers the indoor RH, and is a big cause of people needing to get humidifiers. Since he already has a fresh air intake. using combustion air from the house will increase the amount of fresh air pulled in, and lower the RH more. Which would make him robbing Paul to feed Peter. Currently, his fresh air intake only brings in what his house is able to exhaust. Using indoor air for combustion would increase that intake amount by 30 to 50% maybe more.

Best to have combustion air go only to the furnace, or furnace room.
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Old 09-25-2012, 11:30 AM   #20
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Where to attach Fresh Air intake location on return plenum


OK now I see your point. I would also add that using, already heated indoor air, for combustion may be a waste of energy so, just relocating FA intake in the furnace room is still a good idea.
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Old 09-25-2012, 11:45 AM   #21
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Where to attach Fresh Air intake location on return plenum


FA in the furnace room only, won't get that FA to the other rooms.
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Old 09-25-2012, 12:26 PM   #22
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Where to attach Fresh Air intake location on return plenum


If you go back in the thread there is a separate one for each..FA to return air duct AND CA to furnace room itself.
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Old 09-25-2012, 01:13 PM   #23
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Where to attach Fresh Air intake location on return plenum


I intentionally bought a 80% furnace instead of a 90+% because of the needs for dedicated air intakes and exhaust on a 90% unit. My home had a dedicated fresh air intake that dumped the fresh air into a 5 gallon pail (to stop siphoning) and used a the stale interior air for combustion.

When my 80% unit (Bryant) was installed, the furnace installer did put a vented cover on my pail to keep the intake inside the pail.

Dick
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Old 09-25-2012, 04:38 PM   #24
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Where to attach Fresh Air intake location on return plenum


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If you go back in the thread there is a separate one for each..FA to return air duct AND CA to furnace room itself.
I know. I was just answering to what you posted.
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Old 09-25-2012, 04:41 PM   #25
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Where to attach Fresh Air intake location on return plenum


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Originally Posted by concretemasonry View Post
I intentionally bought a 80% furnace instead of a 90+% because of the needs for dedicated air intakes and exhaust on a 90% unit. My home had a dedicated fresh air intake that dumped the fresh air into a 5 gallon pail (to stop siphoning) and used a the stale interior air for combustion.

When my 80% unit (Bryant) was installed, the furnace installer did put a vented cover on my pail to keep the intake inside the pail.

Dick

That would make it a combustion air intake, not a fresh air intake. Since you wouldn't want fresh air to just stay in the pail.
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Old 09-25-2012, 06:18 PM   #26
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Where to attach Fresh Air intake location on return plenum


OK we got that straightened out..I think...Onwards and Upwards

Did this mainly because I have now included my location and wanted to see if it is now included and it is..yippee kyay!

Last edited by techpappy; 09-25-2012 at 06:20 PM.
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