Finishing a Basement

325_man

Hi,

First, I like to say that this forum has helped me a great deal in the past, and
I hope anyone can give me some more guidance in my effort to finish my basement myself.

So, I am about to start framing the basement, but I notice my builder didn't install many air vents for the basement. There are only 2 opening from the main air duct coming out from the HVAC, one on each end. There are other vents that feed the main floor.

I am thinking to create some rooms in the basement (i.e. entertainment room, a full bathroom, and a big open room). I think each of them needs at least 1 air vent and the big open room needs 2 air vents.

Here are the questions that come to mind at this time:
* Can I just tap the main air duct to create additional air ducts for the rooms?
* Isn't there air pressure calculation that I need to consider? If so, please direct me to sites that can give me guidance.
* Since I live in VA, are there codes, especially for the bathroom, that I need to know before messing around with the existing air duct?

Thanks!
Nick

beenthere

Doubt your existing duct is big enough for the basement also. Should run a new trunk line for it.

325_man

To give context to the existing air ducts (I may use the wrong terminology, so I apologize if I do), here are the pictures depicting my situation and my plan.

I hope someone kind enough to give me some input.

Thanks!
Nick

beenthere

And what size is your existing furnace.

HVACTECH96

Having a clean slate to work with like you have now,you have the ability to do it right and have a second trunk line installed and have it zoned so you can have a nice comfortable lower level to hang out in.

325_man

Here is the info on my existing HVAC. I live in VA.

Goodman GMT070-4B
Heating Input: 70,000 BTU/HR for Natural Gas.
Output Capacity: 56,000BTU/HR for Natural Gas
For temp rise of: 20 - 50

Design Max outlet temp:150F
Motor:1/2 HP
Aux. Limit Setting: 120F
Blower: 10x8
Factory tested external static pressure: 12

The house currently has 2 furnaces, one in the attic and one in the basement.
The information I provide is for the one in the basement.

The living area of the main and the second floor is 3400 sq ft. The unfinished basement is another 1500 sq ft.


Thanks,
Nick

beenthere

If you zone it, it should do ok.

325_man

I am new at this. Could you please explain what you meant by "zone it"?

Thanks,
Nick

TheyCallMeDave

1. Yes, you can tap the trunk duct for additional basement branch ducts.

2. Typically what you do is, install the basement ducts you want...then adjust existing (if they were put in) balancing dampers for all the other ducts so you get enough air pressure feeding your new basement ducts. It will require trial and error . Hopefully you can take air from house ducts that were pushing too much air to begin with, and use it to feed your basement ducts. If there are no balancing dampers installed , you can add them to the first floor branch ducts and adjust them for adequate basement airflow.

3. The only codes you are likely to find for bathrooms, is that : a. You never put in a return in the bathroom b. You add a small exhaust fan in the bathroom typically energized by a wall switch c. Run one supply duct to the bathroom for heat IF the bathroom is on the outer wall, otherwise, it isnt even necessary if its an interior bathroom.

beenthere

it consist of 2 or more motorized dampers that are controlled by a zone panel that the thermostats are wired to along with your furnace and A/C. The damper for the calling zone opens and the other one closes. So air is only blown into the area that needs heat or cooling.

TheyCallMeDave

You could do it this way, but trust me...youre not going to want to go to the expense . Simply adjust manual balancing dampers as ive said above, until you get the amount of air you desire for the basement rooms.

beenthere

And if he has central A/C he has to re-balance the dampers twice a year. Or the basement will over cool too much.

Zone system when done DIY is not expensive. Plus can save on heating and cooling cost since he won't have be heating and cooling the basement to normal comfort level 24/7 if he doesn't want.

TheyCallMeDave

Turning 2 or 3 mechanical dampers by hand can be placed on his seasonal list of things to do , just like changing oil or the air filter in his furnace. I encourage the OP to check into the cost of 3 motorized dampers, thermostats, and his time to install them to see if HE thinks its worth it.

beenthere

The convience alone is worht it.

Not to mention, he would still need to re-open the first floor supplies he choked down, or risk freezing his evap coil.

HVACTECH96

Most finished basements get drywall ceilings and duct chases.So all those dampers are going to be useless there after.Also robbing peter to pay paul usually affects paul quite a bit.