New zone with one vent

tamer

Hello everyone,
I have central HVAC system.
Bosch Gas furnace, 120,000 BTU, forced air, up-flow (Model: BGH96M120D5) with currently 2 zones ( 1st floor w 2 dampers and 2nd floor w 1 damper). Basement has 2 small vents part of zone1 which not enough to heat the basement.
Basement has 1 return. I want to add a 3rd zone for my finished basement (1200 sqft) and close the 2 small exiting vents. I'll use it mainly for heating not AC. I can't run multiple vents in the basement.. I can run ONLY 1 vent and 1 return. Control panel is Honeywell HZ322 and the 3rd zone is free. There is bypass installed connected to the right side of the humidifier ( you should see it in the second picture) .

I have few questions.

1) Is that possible? or it's too much force for 1 vent and it will be short run too
2) If it's doable with one vent, how big is the vent should be and how big is the return?
3) does it matter if I cut it circle or rectangular?

Thanks in advance!

EdTheHeaterMan

It looks like there are 2 dampers for the first floor zone. One to the front of the furnace and one to the rear of the furnace. I believe you are saying that one thermostat opens both those vent dampers.

Second floor has a third damper

You can add a 4th damper for the basement. But will the Zone Control Panel accommodate 3 zones with 4 dampers? It is tough to tell without the model number of the Honeywell Panel.

1) Is that possible? or it's too much force for 1 vent and it will be short run too.

It is possible. There may be too much force if there is no bypass damper installed, or if the bypass damper is not properly adjusted. More info on the existing design is needed in order to answer that definitively YES or NO.

2) If it's doable with one vent, how big is the vent should be and how big is the return?

That depends on several factors. How much heat or cooling is needed will determine the Cubic Foot per Minute (CFM) of air flow. CFM needed will then determine the duct size.

3) does it matter if I cut it circle or rectangular?

Round dampers are available so you can cut a round hole for the new zone.

How many square feet of basement floor will be heated/cooled?

pecmsg

Basements require heat while the upper floors require cooling. 

Install a small mini split and dehumidifier. 

tamer

Basements require heat while the upper floors require cooling.
Install a small mini split and dehumidifier.

No, Only heating during the winter time.

tamer

Thanks @EdTheHeaterMan .

One to the front of the furnace and one to the rear of the furnace. I believe you are saying that one thermostat opens both those vent dampers.
Second floor has a third damper

Yes .. 2 dampers connected to the 1st zone. 3rd damper is connected to zone 2

It is tough to tell without the model number of the Honeywell Panel.

Sorry, I missed it.. It's HZ322 .. and has free 3rd zone now.

There may be too much force if there is no bypass damper installed, or if the bypass damper is not properly adjusted. More info on the existing design is needed in order to answer that definitively

There is bypass installed now, it's part of humidifier (pls see 2nd picture) , is this enough? what kind info do you need? will be happy to answer them. thx

How much heat or cooling is needed will determine the Cubic Foot per Minute (CFM) of air flow. CFM needed will then determine the duct size.

I need to use it only for heating during the winter time. where can I find the CFM.. I'm looking at the manual and seems to be 2290 - https://skipthewarehouse.com/index.php?route=extension/module/mmos_attachmanager/getfile&product_attach_file_id=14441

since it's 2 stage ECM motor for quiet, efficient operation .. Maybe I can run the basement only on 1st stage heating.

How many square feet of basement floor will be heated/cooled?

1200 sqft all open space.

EdTheHeaterMan

There is bypass installed now, it's part of humidifier (pls see 2nd picture) , is this enough? what kind info do you need? will be happy to answer them. thx

The humidifier bypass is not the one you need for the Zone Control. That bypass should be closed for summer operation and open for winter operation.


This is a bypass damper https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Honeywell-CPRD12-Product Overview.pdf

Since the heat exchanger and the evaporator coil need to have a given amount of air flow in order to deliver all the capacity of the equipment, when all the zones are calling, your furnace blower will be set to deliver that amount of air flow. For example: a 3 ton Air conditioner might operate properly with a blower that delivers 1200 CFM air flow. What happens to that air flow when only one zone is open. That one zone's duct work may only be able to handle 600 or 700 CFM. Try to push 1200 CFM through only one zone and the blower will work extra hard, however, the smaller duct system will be noisy and may only allow 1000 or 900 CFM air flow. A bypass damper will open partially to relieve that additional pressure. 600 CFM will go to the one zone duct that is open and the other 600 CFM will bypass to the return. The fan does not work as hard, the one zone operates quietly and the DATS sensor will cut off the compressor if the coil gets too cold or the furnace gets too hot from the short circuit conditioned air in the return.

On a 3 zone system, if the smallest zone is only able to allow 300 CFM of the available 1200 CFM the blower will produce, then the bypass damper will open 100%. If 2 zones are calling, then the bypass damper will open 30%, 40% or 50% depending on the combination of zones that are calling for heat or cooling. When all 3 zones are calling for heat, the bypass damper will be 0% open (100% Closed)

If your system was installed without a Bypass Damper designed for the system to operate in conjunction with the zone dampers, then you may have a noisy system when only one zone is calling.

When you add the third zone, you will want to add the bypass damper that is needed to bypass all the air flow (CFM) the the smallest zone does not use.

pecmsg

tamer said:

Basements require heat while the upper floors require cooling.
Install a small mini split and dehumidifier.

No, Only heating during the winter time.

and what about the spring and fall?

that basement is surrounded by 55°soil, not 70, 80 or 90°air. Because it is cool the RH is higher than the upper floors.

You need a separate heat pump and dehumidifier!

pecmsg

pecmsg said:

tamer said:

Basements require heat while the upper floors require cooling.
Install a small mini split and dehumidifier.

No, Only heating during the winter time.

and what about the spring and fall?

that basement is surrounded by 55°soil, not 70, 80 or 90°air. Because it is cool the RH is higher than the upper floors.

You need a separate heat pump and dehumidifier that can operate independently of the main system!

pecmsg

pecmsg said:

Basements require heat while the upper floors require cooling. Install a small mini split and dehumidifier.

No, Only heating during the winter time.

and what about the spring and fall? that basement is surrounded by 55°soil, not 70, 80 or 90°air. Because it is cool the RH is higher than the upper floors. You need a separate heat pump and dehumidifier!

Now let’s talk winter. 

Again that basement is surrounded by 55* soil not 30* air. 

Again a completely different heat load loss than the upper floors. 

EdTheHeaterMan

I'm not sure I understand what @pecmsg is trying to say. Let me recap it see if I'm getting it

and what about the spring and fall?

that basement is surrounded by 55°soil, not 70, 80 or 90°air. Because it is cool the RH is higher than the upper floors.

You need a separate heat pump and dehumidifier!

or did you mean:

and what about the spring and fall?

that basement is surrounded by 55°soil, not 70, 80 or 90°air. Because it is cool the RH is higher than the upper floors.

You need a separate heat pump and dehumidifier that can operate independently of the main system!

Or perhaps you are trying to say

Now let’s talk winter.
Again that basement is surrounded by 55* soil not 30* air.
Again a completely different heat load loss than the upper floors.

But you might be saying something completely different, Like maybe @tamer should consider a separate mini split for the basement.

Perhaps you could be more specific in your next post @pecmsg

LOL

HVACNUT

Agree with @pecmsg. Install a separate ductless system for the basement. 

If adding the basement to the existing, make sure the DATS sensor is installed, because it's gonna get a workout.

pecmsg

EdTheHeaterMan said:

I'm not sure I understand what @pecmsg is trying to say. Let me recap it see if I'm getting it

and what about the spring and fall?

that basement is surrounded by 55°soil, not 70, 80 or 90°air. Because it is cool the RH is higher than the upper floors.

You need a separate heat pump and dehumidifier!

or did you mean:

and what about the spring and fall?

that basement is surrounded by 55°soil, not 70, 80 or 90°air. Because it is cool the RH is higher than the upper floors.

You need a separate heat pump and dehumidifier that can operate independently of the main system!

Or perhaps you are trying to say

Now let’s talk winter.
Again that basement is surrounded by 55* soil not 30* air.
Again a completely different heat load loss than the upper floors.

But you might be saying something completely different, Like maybe @tamer should consider a separate mini split for the basement.

Perhaps you could be more specific in your next post @pecmsg

LOL

Clear as mud!