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luweee 12-30-2007 01:34 AM

How Do I Install New Duct Lines For My Finished Basement?
I am finishing my basement and am ready to install my HVAC... house is 3 yrs old.. I want to install new duct lines into my newly framed bedrooms, bathroom, family room and exercise room. I will be plugging the 3 existing that the builder put into the UNFINISHED BASEMENT. Then I will run 6 new supply lines. I see that the builder installed duct lines both ways.. some coming off the top ... some coming off the side. I, of course want to come off the side. is this going to affect efficiency REAL BAD? And, coming off the top does not look feasible.

Thanks in advance!

bigMikeB 12-30-2007 07:49 AM

The most probable answer is that the duct work isn't sized to carry the basement and the three runs that were there were just to dump some a/c air, so best of luck with trying to balance it out after.

luweee 12-30-2007 11:10 AM

Thanks Big mikeb for a fast response.

i forgot to tell you i had the original installers (they are very reputable here in Omaha NE) to give me a quote for installing the HVAC for my basement. they said what I have already in place is fine and would handle the load (house is only 3 yrs old too). they told me how many lines and where they were going to run them. From that i had a couple of questions stemming from the info they gave me. FYI i am using insulated flex pipe UL181 approved, mastic UL181 approved, zip ties, and code557 duct tape ul 181 approved. my house is a ranch 2100sft. upstairs.
The basement 2100 sft. (only finishing 1400 in the basement) 2 bedrooms @225sft. bathroom @ 60 sft. exercise/storage room @180sft. family room w/bar area @ 700+sft.

my questions are.

1. my main trunk line narrows at the last 9 feet from the far end and, i want to tap off 3 lines in that area.. is this okay? also... i noticed on the original upstairs ductlines they tapped off some duct lines from the side and some from the top... can i tap all mine off the side?... will this affect the efficiency real bad?

2. is there a rule of thumb on how far away you need tap each line? i.e. 6inches between tapped duct lines?


coolmen 12-30-2007 01:40 PM

A finished basement BELOW grade does not need much heat and very little cooling. I assure you that if you have a single zone system on a 2 floor house you will creat problems to the 2nd floor. 6 supplys is WAY to much. I would just rework what is allready feeding the basement. remove and relocate or extend to where you need it. Ansd dont forget that the mechanical room cumbustion air must be addressed.

bigMikeB 12-30-2007 02:08 PM

Good advice.

luweee 12-30-2007 06:13 PM

Thanks Coolmen and BigMike

I see where your coming from. I will close off and reroute the 3 existing and add only one more. As for the return lines/vents... I had a plan for that. I have a louvered door installed going from family room to the mechanical room, also, i plan on installing a large return vent on the lower part of the wall (an inside wall) in the large family room.

I also have my basement framed for an electric fireplace in the large family room... I will also put 1 1500 watt baseboard heater in the family room... 1 baseboard heater in each of the bedrooms too. I am going with electric because since I have a heatpump I get 1/2 price on electric bill in winter time.
If I had my basement finished when they built the house would they have put 2 zones in?


forgot to ask you... is a supply line needed (for code) in the bathroom? I know it needs to be vented to the outside... in my case a 4" fan forced line is needed ( im using a broan).

Back to the 2 zone deal that you were referring to in your last post coolemn... is this a common thing to do? does it require 2 heaters/airconditioners? Seems expensive. I dont know what im talking about thought maybe you experts could inform me.

luweee 12-30-2007 09:55 PM

Coolmen and BigMike

I have another question.... if i did want to use a couple more lines ... could i use electronic dampers and or inline duct fan boosters? im just kicking up some ideas.

also forgot to tell you that my basement is not completeley below grade I have 9ft ceilings and i also have windows that are about 42 inches from floor on 3 sides of my finished basement. i believe there called egress (SP?) windows that qualify it for legal bedrooms. i dont know if any of this makes a difference on what ive been telling you.

bigMikeB 12-31-2007 08:24 AM

What size is the furnace you have? It sounds like you would need @48,000 btu's for that space. At that size of a space I would add it's own unit if it was my house and I was going to be there for a while.

hvac122 12-31-2007 10:55 AM

I come from your neck of the woods and when we size houses we include the basement in the fold even if it will be finished later. We size the duct for a future finish and just cut a few registers in the duct to temper the basement until it gets layed out and finished. It sounds like your contractor did just that and the extra runs will not make much difference upstairs.

Remember that without zoning the basement from the upstairs there will be a temperature difference of around 8 degrees. Sounds like you will have that covered with the electric baseboard so I would go with it.

luweee 12-31-2007 01:44 PM



i see your from lincoln... yeah im here in omaha.
there are 3 vents in basement from existing ... so if i reroute those 3 and add 3 is that too much? i have a return planned... read above for square foot info. i think i might go with 24vac dampers on 3 of them. to help in summer time... in case it loses AC up stairs... maybe all 6 i'll see.

all of everybodys help has been very useful and informing.

thanks all to have replied

hvac122 12-31-2007 02:14 PM

Most likely the duct and system was sized for the whole house although I couldn't know that for sure. Its just the way we do things in Lincoln so I would guess Omaha is the same. If you are going to spend the money on dampers then I would zone the whole house and have a real comfort control system. We use honeywell zoning and you can get dampers that can be cut into every heat run and a 2 or three zone controller. That way you could have a thermostat for the basement and the upstairs.

luweee 12-31-2007 09:00 PM


those dampers are expensive $50 a piece. 300 just for the basement... might need $1500 to do all of them.... nah .. i think i will pass on the dampers HVAC122. I will do as you said. I know when i called for a bid .. the guys that built my house gave there bid and they said originally it was built for a finished basement.

one question for ya HVAC122 i am cutting my runs into the side vice the top.. i noticed they did both top and side for the upstairs. will this make a difference? also, is there a minimum distance between 6" starting collars that has to be kept?

THanks hvac122

hvac122 01-01-2008 07:52 PM

In the side or the top, without seeing it, is hard to tell how it may effect your system. The idea is to have as few bends as possible for proper air flow. You can put your takeoffs as close as needed if duct is sized right.

I see you are planning on using flex duct. This will greatly cut down your air flow to each room and may even require mor runs. I would highly recommend using pipe and elbows. Good luck.

luweee 01-01-2008 09:29 PM


yes thanx for the info. my brothers best friend is a hvac tech in Sioux falls
he said the same thing

look like i will be using the straight pipe.

thanx again hvac122

luweee 01-04-2008 02:12 PM

HVAC 122

I have a question for ya.
My brothers friend has offered to phone a HVAC place here in Omaha where i can pick up my supplies.

Will i be able to get my supplies cheaper than i will get them at lowes.... or atleast the same price?

My gut tells me to go to lowes and get my stuff... its only bout $250 for what i need. My brother inlaw who is a dry waller/builder or what ever he does. has loaned me his hvac cutter... its a hand held power tool of some type that .. all you need to do is to punch a hole then you can start to cut your hole that you templated out...

thats all besides my point... my question is .. is it worth the offer to get it at a wholesaler as opposed to lowes?

Thanks hvac 122.... as far as HVAC goes.... YOU ARE THE MAN!

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