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Old 08-14-2007, 04:32 PM   #1
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Whole House Air Cleaner


We have a 11 y.o. Day & Night furnace (one of Carrier's D&N/Payne/
Bryant brands) model 350MAV, 60K input, 56K output, and a 3 ton AC.

We are getting three bids to install a whole house air cleaner.

Any preferences between the Aprilaire 5000 and the Carrier?

All three contractors would install the unit differently.

#1 would remove the furnace from the plywood stand that it is on,
place the air cleaner on top of the return hole, and set the furnace
back on top of the air cleaner.

#2 would mount the air cleaner on the side of the furnace
(at the bottom of the right side) and therefore not have to
remove the furnace. They said that the manufacturer allows that.

#3 would mount the air cleaner inline with the sheet metal
return duct which is near the side of the furnace.
They wouldn't have to remove the furnace either.

Is one of thse methods preferable over the others?
Is one of these methods not advisable?
Thanks.

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Old 08-16-2007, 04:58 PM   #2
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Whole House Air Cleaner


The filter should ALWAYS be in the return.....and easy to get too..........

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Old 08-16-2007, 05:41 PM   #3
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The first guy seems concerned with the furnace being on a plywood box, not seeing the job myself, it brings some items up. Can you post a pic of the current set up?
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Old 08-16-2007, 11:23 PM   #4
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Maybe I didn't describe this well. In the garage the furnace sits up on a sealed plywood box. Is this called a plenum? I believe that it is code that furnaces and water heaters cannot sit on the garage floor. The plenum is roughly 2 feet high, 5 feet wide, and 2 feet deep. It is, more or less, air tight.

The return sheet metal duct comes out of the wall between the house and garage, makes a 90 degree turn, and goes down through the top of the plenum. It joins the plenum immediately to the side of where the furnace sets.

A rectangular hole is cut in the top of the plenum by the furnace contractor. The furnace sits on top of that hole. Return air goes into the plenum from the return duct. The furnace fan takes air up from the plenum, heats or cools it, and sends it back to the house via the supply duct.

Contractor #1 said that he would temporarily remove the furnace from the plenum. He would set the air cleaner on the hole where the furnace was. He would then set the furnace on top of the air cleaner, in the same place that it was, but several inches higher. I guess he has to cut an appropriate number of inches off the supply duct to make up for that.

Contractor #2 would not do that. He would cut a hole in the side of the furnace, at the bottom, and mount the air cleaner vertically on the side of the furnace. He said that the furnace manufacturer allows that. I have gone to the furnace website and they have pictures of that configuration. In this method, the plenum is no longer used, since the return sheet metal duct would be changed to make a 90 degree turn to go into the air cleaner, instead of going straight down into the plenum like it used to do.
'
Contractor #3 proposed something even simpler. He would simply set the air cleaner on the hole that the return duct goes down into now. The air would go from the return duct, through the air cleaner, into the plenum, and into the furnace.

Three contractors, three different solutions. This is what drives homeowners nuts. And this is why some homeowners never end up having a job done. You can't even get agreement from the contractors on how it should be done.
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Old 08-21-2007, 12:42 PM   #5
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Let me restate the question.

Where should a whole house electronic air cleaner be placed?
1. Below the furnace (between the furnace and the plenum),
which requires removal of the furnace.
2. In a new hole cut in the side of the furnace. I have checked
and the furnace manufacturer says that this _is_ allowed.
3. In the sheet metal return duct coming from the house to
the furnace.
4. Some other place.
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Old 08-21-2007, 02:24 PM   #6
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Quote:
Originally Posted by joee View Post
Let me restate the question.

Where should a whole house electronic air cleaner be placed?
1. Below the furnace (between the furnace and the plenum),
which requires removal of the furnace.
2. In a new hole cut in the side of the furnace. I have checked
and the furnace manufacturer says that this _is_ allowed.
3. In the sheet metal return duct coming from the house to
the furnace.
4. Some other place.

I have seen it done all three ways and all three ways will work. I wouldn't go the first route. You can scratch that off the list. It is just overkill at this point. Is the plywood box sealed and insulated? In older homes, they would just seal the box and not put any insulation. If the box was sealed and insulated, I would go with contractor three and just cut it into the return plenum. Make sure he transitions the duct into it though. The filter is not going to be the same size as your duct. I have seen guys just cut the duct the height of the filter and just stick it into the duct. The then just seal the portion the remaining portion that overhangs the duct. You will not get full use of your filter this way. What he needs to do is cut out a three foot section or more depending on the size of your return duct. He will then have to transition the duct into the filter from both ends. I hope that made sense. If the plywood isn't sealed and you do not have a 2000 cfm unit (5 ton cooling capacity), I would cut it in the side. It really depends, but I don't think you can go wrong with choice two or three. Now that I think about it. This is what I usually do. I haven't seen your setup so please keep that in mind. To save space of the overall unit size (unit plus return duct). I usually cut a hole in the side of the unit. I will then build a box made out of duct and attach it to the side of the unit. The filter then sits horizontally on this box. I will then tie in the duct work into the top of the space guard. It looks clean and professional in my opinion. I will only sit a unit on top of a filter if it is designed specifically for that unit (i.e. the manufacturer of the unit makes it). I do this a lot with Trane perfect fit type filters.

Last edited by Malcolm; 08-21-2007 at 02:26 PM.
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Old 08-22-2007, 11:35 AM   #7
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Thank you for your response. The plywood box is sealed but not insulated. It wasn't sealed until I started working on this project. It had huge cracks at most of the interfaces (vertical and horizontal). On the outside of the box I caulked the large gaps and used primer paint on the small cracks. It seems pretty much airtight now.

The garage is now fully insulated, so the temperature doesn't get extremely hot or cold. When it is extremely hot outside, the garage gets to around 80. I'm not sure about the winter, but probably in the low 50's. The house is 11 years old, and the garage was mostly uninsulated previously and the plenum had huge gaps. So both are now better than they have been in past years before we moved here. One thing that concerns me a little is that the garage has some (probably small) amount of mildew and mold in it, simply from being exposed to the outside air and surrounding ground. The previous huge gaps in the plenum and _numerous_ large gaps in the sheet metal return duct joints have recently been fixed. For 11 years both sucked lots of garage air into the furnace, bypassing the expensive, high quality pleated filters that I use. (The filter is in the return vent, which is inside the house.) I am concerned that the plenum might have some mildew or mold in it. I am having all the flex supply ducts in the attic replaced with new, high R value supply ducts because of this concern.

Both bid #1 (under the furnace) and #3 (in the return duct next to the furnace) would continue to use the existing plenum/plywood box. Bid #2 (into the side of the furnace) would bypass the plenum. Perhaps that's a good thing.

Last edited by joee; 08-22-2007 at 11:42 AM.
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Old 08-22-2007, 02:26 PM   #8
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Quote:
Originally Posted by joee View Post
Thank you for your response. The plywood box is sealed but not insulated. It wasn't sealed until I started working on this project. It had huge cracks at most of the interfaces (vertical and horizontal). On the outside of the box I caulked the large gaps and used primer paint on the small cracks. It seems pretty much airtight now.

The garage is now fully insulated, so the temperature doesn't get extremely hot or cold. When it is extremely hot outside, the garage gets to around 80. I'm not sure about the winter, but probably in the low 50's. The house is 11 years old, and the garage was mostly uninsulated previously and the plenum had huge gaps. So both are now better than they have been in past years before we moved here. One thing that concerns me a little is that the garage has some (probably small) amount of mildew and mold in it, simply from being exposed to the outside air and surrounding ground. The previous huge gaps in the plenum and _numerous_ large gaps in the sheet metal return duct joints have recently been fixed. For 11 years both sucked lots of garage air into the furnace, bypassing the expensive, high quality pleated filters that I use. (The filter is in the return vent, which is inside the house.) I am concerned that the plenum might have some mildew or mold in it. I am having all the flex supply ducts in the attic replaced with new, high R value supply ducts because of this concern.

Both bid #1 (under the furnace) and #3 (in the return duct next to the furnace) would continue to use the existing plenum/plywood box. Bid #2 (into the side of the furnace) would bypass the plenum. Perhaps that's a good thing.

If it is not insulated, I would bypass the plywood box. I know you said you sealed it, but they are a pain to seal even if you have the furnace off the plywood stand. Just have the contractor cut a hole in the side of the furnace and seal the hole in the bottom of the furnace.
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Old 08-22-2007, 04:24 PM   #9
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What size (btu's) is the furnace?
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Old 08-22-2007, 05:18 PM   #10
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Furnace: 60K input, 56K output
AC: 3 ton

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