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Old 09-05-2020, 11:21 PM   #1
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DIY Zoning


I have a single stage forced air gas furnace and air conditioner (Goodman GKS90703BXAH). The supply is split into two trunks, a 20"x8" feeding the downstairs (1000 sq ft) and basement, and a 12" round feeding the upstairs (1300 sq ft), so I feel like this should not be too difficult to do.

There are manual dampers, and normally I can make summer and winter tolerable by adjusting, but on warmer or colder than average days, its easy to have a 5-7 degree imbalance. And during the seasonal changes it is all over the place. For reference I live in Indiana, near Chicago. Weather is very dynamic.

I had a local HVAC company quote the zoning ($2000), but they weren't going to add any bypass. I would think this is needed, correct?

To me the project looks straight forward, and with materials only being ~$600, would like to try myself.

This is the equipment I was thinking:
https://www.supplyhouse.com/Honeywel...nd-HZ311-Panel
https://www.supplyhouse.com/EWC-20X8...torized-Damper
https://www.supplyhouse.com/EWC-12RS...torized-Damper
Ecobee thermostats for both levels.

Regarding bypass, I have also seen the iO systems, where they add a sensor to measure static pressure, and will slightly open the non-calling zone until pressure is relieved. I like this concept, but haven't found a place to buy the panel and sensor. Is there any way to do this on Honeywell equipment?

My furnace is described as multi-speed, but this looks like it is changed by wiring only (and selected based on the size of the air conditioner). So the zoning system cannot control this.

Any insight or recommendations would be appreciated.
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Old 09-06-2020, 12:14 AM   #2
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Re: DIY Zoning


Is the upstairs not cooling and heating properly?

Your temperature imbalance is likely caused by an undersized trunk line going to the second floor, relative to the first.

20x8 flows around 50% more air than 12" round.

Your basement probably has minimal heating needs and most of it is going to the first floor.

You should know -> other things can drive temperature differences between floors:

1. Insufficient attic insulation and for summer, ventilation
2. No return air on the second floor

3. Excessive air leakage; the stack effect can make the basement/first floor much colder due to air leaking in in winter. In summer, the stack effect is reversed - air leaks into the second floor and out the lower levels, making it hotter upstairs.



It's better to fix the cause if it's within your budget than resort to zoning.

I believe that your system is not a good candidate for zoning - some here will disagree. The furnace is single stage @ 64.4k btu output, should have 1000 to 1200 cfm ideally*. I'm betting you have a 2.5 or 3 ton a/c -> similar airflow requirements.

*The absolute minimum required by the manufacturer is around 920 for a 65F temperature diff between supply and return. The optimal temp diff is 50F, the middle of the rise range = around 1200 cfm. (numbers are rounded)

Your 12" duct feeding the second floor is only good for around 650 cfm at the highest size factor/restriction level recommended. (0.1" drop per 100 ft which some say is too high)
When only the second floor zone is calling, quite a bit of air will have to be bypassed into the return duct (bypass system) or bled into the main floor/basement zone depending on the setup.

The latter reduces the effectiveness of the zoning system.

The former can cause the furnace to overheat/evap coil to freeze in cooling mode unless a discharge air sensor is used to cycle the heating/cooling during a continuous call - which is hard on the equipment. The bypass reduces efficiency too.
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Last edited by user_12345a; 09-06-2020 at 12:28 AM.
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Old 09-06-2020, 03:05 PM   #3
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Re: DIY Zoning


Thanks for the feedback, 12345a. You confirmed what I thought, the bypass will be necessary. Although it has some draw backs, it doesn't seem good to run without it. How do I go about picking the size for the bypass?

I do plan on putting in a discarge air temp sensor.

The attic is insulated to R60, and as far as I can tell all the duct work is well sealed. There are air returns on the second floor. The hose is newer (5 years old), and hopefully everything is still in good condition.

I really doubt increasing the size of the duct work or chasing leaks is in my budget. That would involve opening up walls.
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Old 09-06-2020, 05:21 PM   #4
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Re: DIY Zoning


I'm not familiar with bypass sizing, just the general concepts and someone else (beenthere?) could give you much better info on that if you go that route.

A potentially better option than a bypass - perhaps dumping excess air into a common hallway (maybe between floors if ducting it is not horribly expensive) instead of than directly into the return

One thing you should definitely get if you end up doing zoning - a panel that can stage the furnace. When your existing furnace needs to be replaced, you can get a 2-stage which needs far less airflow on low and the panel doesn't allow it to hit high until unless both zones are calling.

-----------------------
Do you by any chance have any main floor closets that could be used to run additional ductwork up at a lower cost? (ie no major bulkheads required?)

Right now, does your 12" going upstairs go into the attic and branch off into trunks, or is it all in the joist space between the first and second floor.
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Old 09-06-2020, 06:22 PM   #5
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The 12” round goes up to the attic and branches off from there to the rooms.

No closet to utilize.
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Old 09-06-2020, 06:42 PM   #6
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Re: DIY Zoning


Part of your problem may be poorly done flex in the attic - it needs to be stretched and have straight runs, elbows should be metal. Flex needs to be sized larger to get the same airflow as metal.

Capacity loss to the attic is probably not helping matters either.

It's a good idea to check out what's up there before trying zoning -> sizes, how the ducts were run -> you may be able to make improvements.

I really think even with a bypass your system is not a good candidate zoning and it can make a bad duct system worse.
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Old 09-06-2020, 06:53 PM   #7
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All of that duct work is covered under many inches of blown in insulation. Unfortunately that is beyond my physical capability to inspect much more than looking at it through the attic access door. But I expect it’s just done to code, not done as well as we all would like.

If zoning isn’t the fix, what is the best way to tackle the temperatures disparity between levels. I already run my fan full time, by the way.

I am now questioning why the HVAC guy didn’t look in to this before quoting the zoning.
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Old 09-06-2020, 06:58 PM   #8
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Re: DIY Zoning


Quote:
If zoning isn’t the fix, what is the best way to tackle the temperatures disparity between levels. I already run my fan full time, by the way.
It's hard to tell without a thorough inspection of what you have.

I imagine any fix won't come cheap.

Loose fill attic insulation can be moved around, it would be a huge pain to inspect and not diy friendly.

Unfortunately, this stuff is often not done very well as granite countertops sell houses, not good heating systems.

One thing you can easily do is remove the register covers upstairs and check the branch line sizes/type -> post back with what you have.

Is the 12" pipe going up to the attic metal or flex?

To be clear, your problem is that the second floor isn't heating/cooling properly, correct?
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Old 09-06-2020, 07:01 PM   #9
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Correct, the second level is often several degrees hotter in the summer, and several degrees cooler in the winter, compared to the main level. On days it is particularly hot or cold outside, this difference can be 5-7 degrees.

A couple weeks ago we were constantly in the 90s for a high, and in the lower level would be a comfortable 72 and the second level a miserable 79.
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Old 09-06-2020, 07:06 PM   #10
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Re: DIY Zoning


How's the airflow upstairs?

Get the duct info when you have a chance - what you can see at the registers with the grills removed.
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Old 09-06-2020, 09:35 PM   #11
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Re: DIY Zoning


Airflow upstairs seems okay, but I have never measured. I will take a look at the ducts soon.

I have manual dampers on the two trunks. If I close off the first level completely and leave the second level open, and the system does not shut down, can I assume everything will work okay? Or worth picking up an inexpensive manometer? I saw these for $35 on Amazon.
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Old 09-06-2020, 09:47 PM   #12
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Re: DIY Zoning


Quote:
I have manual dampers on the two trunks. If I close off the first level completely and leave the second level open, and the system does not shut down, can I assume everything will work okay?
For heating, you have to run the furnace for a good 15 minutes and measure the temperature difference between the supply and return, see if it's within the temp rise range on the rating plate and preferably closer to the middle of the range than the max.

The thermometer can't be within line of sight of the heat exchanger - 1 foot or so down the trunk line. The btu input needs to be correct for this test to be valid and for that you need to clock the gas meter first to verify.

Clock gas meter: https://hvactechhangout.com/home/sys...k-a-gas-meter/
*Don't time the fastest moving dial for only one turn, not accurate - need a few turns averaged.
temp rise test: https://www.structuretech.com/blog/diy-furnace-test

For cooling, you have to check the a/c size and ideally measure static pressure with a manometer/tips and look at the fan performance table (look up furnace model to get it) to make sure the airflow is at least 350 cfm per ton.

You can find videos showing how to do this.

Now, you can estimate airflow based on heating temp rise -> CFM = output BTU / (1.08 x delta-t), but the cooling speed needs be temporarily connected to the heating terminal on the control board.

Can also see if the suction line is frosting.

I doubt that you'll be able to get away with completely dampering off the main floor/basement trunk line. You'll have to experiment.

This is probably more info than you want, but better to do things properly than risk damage.
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Old 09-07-2020, 05:06 AM   #13
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Re: DIY Zoning


Based on a 50F temp rise in heating mode. In theory both of the zones would be close or just above 60% of the air flow needed for the furnace or A/C, and not require a bypass. However, for noise issues, you would want a 8" bypass. An 8" bypass will bypass up to 400 CFM of air.


Honeywell sells a bypass that is easy to set up, so that it only opens if the static pressure gets to X ".


Your 12" round to the second floor, probably should have been a 14", but you would still have an imbalance in temp between the 2 floors.
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Old 09-07-2020, 10:06 AM   #14
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Re: DIY Zoning


Quote:
Based on a 50F temp rise in heating mode. In theory both of the zones would be close or just above 60% of the air flow needed for the furnace or A/C
Are you assuming the higher static will push a lot more air through that 12"?

How much air do you believe is acceptable to just dump into the return?
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Old 09-07-2020, 10:46 AM   #15
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Re: DIY Zoning


It is sounding like my best option might be to have a dump zone, or better yet, find a place to buy the iO panel with static pressure sensor to partially open the non-calling zone.
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