New 22' Trunk Line

**beenthere** · 05-31-2010, 07:10 PM

Keeping the furnace jacket off the floor, helps to prevent rusting out. They make plastic feet for this.

Yes, thermostat wire comes in 5 wire. Should always run extra. You would be surprised how often having extra wires has saved another thermostat line from having to be ran.

unixb0y · 06-01-2010, 12:14 PM

Quote:

Originally Posted by beenthere

Keeping the furnace jacket off the floor, helps to prevent rusting out. They make plastic feet for this.

Yes, thermostat wire comes in 5 wire. Should always run extra. You would be surprised how often having extra wires has saved another thermostat line from having to be ran.

I was planning on running 2 cables(each with 5 wires) to future proof things.

In reading the specs, it looks like the furnace will use 8.7A. Should 14.2 be ok or should I use 12.2?

**beenthere** · 06-01-2010, 03:01 PM

14/2 is fine for a furnace.

unixb0y · 06-03-2010, 01:32 AM

I need to tie into square stack boots that are 3x12 inch. There doesn't seem to be anything on the market that is affordable that will tie in to round duct.

So what I was going to do is reuse the stack boots, add a 3x12 to 3x10 reducer and then add a universal boot to convert the 3x10 to either 4,5 or 6 inch round pipe.

I spent some time tonight trying to build a paper template for a 3x12 to 3 1/4x10 reduction. I was attempting to make a one piece reducer that I could bend with a 24" brake.

So far, I haven't been successful designing a reducer with the least amount of pieces.

At this point, I think I'm going to make a top, bottom, and 2 sides with 90 deg bends and screw/mastic the reducer.

I'm looking for suggestions on how to build the reducer with the least amount of pieces and screws

**beenthere** · 06-03-2010, 06:10 AM

Can you get a 3¼X12 boot to fit on the 3X12 stack?

A reducer like that, is generally made from 1 piece of metal. Just have to decide if you want it to reduce to one side, or reduce tot he middle/center.

unixb0y · 06-03-2010, 10:22 AM

Quote:

Originally Posted by beenthere

Can you get a 3¼X12 boot to fit on the 3X12 stack?

A reducer like that, is generally made from 1 piece of metal. Just have to decide if you want it to reduce to one side, or reduce tot he middle/center.

I'd like to reduce it in the middle as the duct is located between floor joists. So far I have not been able to find a template or stocked piece online.

unixb0y · 06-09-2010, 12:01 PM

Well I managed to get the reducers made for $10 each. So that was nice.

Now I'm wondering if It a good idea to have a take off on the top of the supply plenum?

**beenthere** · 06-09-2010, 01:53 PM

50/50.

A single take off or 2, is no real problem.

unixb0y · 06-09-2010, 02:49 PM

Quote:

Originally Posted by beenthere

50/50.

A single take off or 2, is no real problem.

This particular take off will only need to be 3 feet long.

It will be going to an inside wall in the living room. I have an older house and in this case, I'll be working with what I have.

My concern is the noise with this particular register. Am I wrong to assume that this takeoff/register will get the brunt of the pressure and therefor be noisy?

**beenthere** · 06-09-2010, 03:00 PM

It could be noisy only being 3 foot long. Being flex duct will help to minimize some of the noise.

unixb0y · 06-09-2010, 05:23 PM

Quote:

Originally Posted by beenthere

50/50.

A single take off or 2, is no real problem.

Does it matter if the take off is on the side or the top of the plenum?

**beenthere** · 06-09-2010, 05:51 PM

Side has less turbulence from velocity.

unixb0y · 06-17-2010, 12:22 PM

Is the using the duct calculator in HVAC calc good enough?

**beenthere** · 06-17-2010, 12:40 PM

Unfortunately. It leaves a lot to be desired.

Your furnace blower. Won't be able to work against the amount of static pressure that a 4" pipe moving 85 CFM would need.
It would take a supply static of .5" to move that much air through a 4" pipe. Add on what the return would be. And its too much for the blower.

On some 6" runs. Its hard to get a full 85 CFM through them. Depending how long they are, and if they have any ells in them.

unixb0y · 06-17-2010, 03:11 PM

Quote:

Originally Posted by beenthere

Unfortunately. It leaves a lot to be desired.

Your furnace blower. Won't be able to work against the amount of static pressure that a 4" pipe moving 85 CFM would need.
It would take a supply static of .5" to move that much air through a 4" pipe. Add on what the return would be. And its too much for the blower.

On some 6" runs. Its hard to get a full 85 CFM through them. Depending how long they are, and if they have any ells in them.

I was going to disregard hvac calc and use 6" for the upstairs runs. 1 room run is 10' while the other 2 rooms are 14'.

All the other runs are shorter. I was then going to use 5 inch on the main floor and 3 inch in the basement.

Can the CFM in hvac calc be trusted? Should I go off of that to figure things out?

Is there anything I can use that's inexpensive to figure it out myself?