Moving furnace into the attic, what should I look out for? Feedback on plan...

[eecsflyer]

I am planning on installing my 3 ton Trane XE 80 furnace into the attic where I plan on installing all new ductwork. The current ductwork in the crawlspace is covered in asbestos and the wonderful contractor that flipped the house though it was OK to leave them all torn up. The crawl space is tiny, so going up in the attic feels like the best choice, so am looking on some advice.

Furnace:
3 ton Trane XE80
Lennox Electronic Air Cleaner

House Details
1,200 sq feet in San Jose CA
3 bdrm (~120 sq feet each)
2 baths (40 sq feet each)
Kitchen / dining room / living room area is (630 sq feet)
I have a converted garage with a seperate furnace feeding one 8" flex line to the living room.

You can see the diagram here

https://docs.google.com/drawings/d/1...?w=1344&h=1008

Questions
1. I have blown cellulose insulation in my attic. The little paper bits kind of fly around in the air a bit. Do I have to worry about the little bits of it getting into my furnace?

2. Is my design OK?
Here is a diagram, https://docs.google.com/drawings/d/1...?w=1344&h=1008

Supply (mostly metal):
BD1/BD2: 10" trunk from supply split into 2 8" runs to each room
BD3: 8" line straing from supply plenum
BA1/2: 4" line to plenum
Dining Room: 8" line form plenum
Living room: 10" line from plenum into a 10" by 10" register boot (Would it be better to split this into two 8")

Return:
16" flex

What are the biggest concerns I should have about putting the furnace in the attic?

Thanks for the help.

Regards,
Wojtek

[kdean1]

Duct sizes are determined by calculating how much air flow each room needs rather than big, bigger, biggest. Has anyone done a load calculation for the house? Or a manual D duct design?

[toocoolforschool]

The first thing I would do is call an abatement team because your house has hazardous waste.

[rider77]

I wonder what the load calc will show for sizing once the unit and ducts are put in a scorching hot attic.

[eecsflyer]

I wonder what the load calc will show for sizing once the unit and ducts are put in a scorching hot attic.

Will the temperature of my attic affect the load calc of my furnace? I do not intend to add A/C, so I just care about heating.

The way I ran my calculations is I distributed CFM evenly across the rooms based on area and followed the duct sizing to CFM mapping in this chart, http://buildingincalifornia.com/wp-c...zing-chart.pdf.

Is this going to be off significantly? I am hoping I can just adjust my dapers, which I will have for every run in case air flow is off somewhere... I am just hoping to be close enough.

[rider77]

Is this a DIY project?

[eecsflyer]

Is this a DIY project?

Yes. I have a problem with being an over-ambitious engineer maybe... So my house is fairly well balanced with the furnace in the center, so I thought it would not be that difficult to go wrong...

So if I can have one question answered. How bad/good of an idea is to run a 10 inch line to a 10 inch register in a big room vs splitting it into two 8" supplies into two registers?

BTW I have a couple HVAC guys I met at the supply store yesterday coming over to help me install the stuff today. So I will have some help...

[rider77]

Your duct load calculations will show what duct you need and where. The site doesn't allow any DIY advice on equipment or modifications.

[beshvac]

If you are an engineer, you should know that the actual loads on the rooms and cfm requirements are not proportional to the square footage.

[toocoolforschool]

An engineer would also know that the communist state of cali would love to hear about someone doing a non permitted job in an attic with loose asbestos floating around. Its your family.

[energy_rater_La]

cellulose in attic
asbestos in crawlspace