I have a ranch style house (built in 1996) that is roughly 1,500SF. I also have a 3 ton Comfortmaker A/C unit and a comfortmaker RPJII airhandeler located in the attic. The air handler is located right above the master suite. I am intrigued by zoning after reading a few posts. Essentially, I have two trunk lines connected to the supply plenum off the furnace. All ductwork is flex. Also, the one thermostat is located in the dining room on the complete opposite side of the house as the master suite is.
1. First trunk line- 10" and runs to the master suite. It connects to a metal "distribution box" which has five branches (4", 4", 6", 6",6"). The master suite gets good air flow.
2. Second trunk line- 14" and the run goes to two distribution boxes. The first distribution box it goes to has three branch runs off of it to the side (7", 6", 6"). The end of this first distribution box is connected to the second distribution box by a 14" flex duct. This second distribution box has four branches off to the side (6", 6", 6", 4"). This feeds the rest of the house (two bedrooms, dining room, living room, kitchen, bathroom and sunroom). The area this trunkline feeds does not get adequate airflow in general and is very unbalanced relative to the master suite. In other words, when the system calls for cooling, the master suite gets very cold while the rest of house remains hot.
Basically, I would love to zone my system. I would like the make the master suite one zone and the rest of the house another zone. I would like to zone the other two bedrooms, but this is not completely necessary.
Here are my questions:
1. Would I install the motorized dampers on the two trunk lines coming off the plenum? (10" and 14" supply trunk lines)
2. If that is the case, it does not appear that Honeywell makes a 14" round motorized damper. Would I need to install dampers on the branch runs (i.e, the 6" runs instead)?
3. I am a little unclear as to how the motorizing dampers are installed. As I mentioned, I have flex duct. My assumption is that I remove the flex duct from the takeoff on the plenum, install the motorized damper to the takeoff on the plenum and then connect the flex duct to the motorized damper?
I appreciate any advice you can give to me.
2. They do make a 14" round damper
3. Yes, that is how you install the damper. I would pull the flex off of the duct tap/collar. Mount the damper onto the tap and screw it into place. Make sure the screws do not hit the damper. Fold the insulation and silver lining back to expose the black liner. Expose enough of the black liner to equal the length of the damper. Cut away some of the black liner (do not cut the insulation of silver lining). After you connect the black liner to the damper (panduit strap and tape), pull the insulation and silver lining over the damper and tape it to the duct plenum. Cut out a small section to expose the damper motor. Strap the damper to the trusses/rafter to support the weight.
You are having hot and cold spots due to a poorly designed duct system. It is expensive to install a zone system. You could try to balance your system first by doing some duct modifications. The easiest and most cost effective thing you could do is install a 10" manual damper to cut off some of the air flow into the master bedroom. It really isn't a good idea to just zone one bedroom. You will also need to install a bypass damper (barometric damper), if you decide to install a zone system.
Honeywell makes round zone dampers up to 20" that I know of.
The areas conditioned by your 14" zone aren't balanced to your master suite because the ducts are sized wrong.
Zoning is more then just installing dampers in your supplies. If you just do that. You'll have lots of problems heating or cooling your house.
Need info on your return set up.
You'll also need a bypass damper to zone your house.
I have thought about the 10" manual damper before as well but was concerned about the restriction in airflow and subsequent damage to the heat exchager and/or compressor. I guess if I did a manual 10" damper, I would need to install the bypass damper as well just to be safe?
Thanks for your response beenthere. Please see my responses below.
What size ducts are attached to those return grilles.
Your supplies off of the 14" are too small. Or they would cool that area at the same rate as the bathroom.
4" flex is about 30CFM.
5" flex is about 50 CFM
6" flex is about 80 CFM(on a good day)
7" flex is about 115 CFM
10" flex is about 330 CFM
14" flex is about 780 CFM
So you have 2-4" and 3-6" branches off of the 10" flex for your master suite area. Or about 300 CFM.
For the rest of the house you have 1-4", 5-6" and 1-7". About 545 CFM.
So your master suite's supplies are close to what the 10" flex can handle.
But the supplies of the 14" are not close to what the 14" can handle.
So your system is imbalanced, because the supplies are undersized for the rest of the house.
I'd redo the supplies to the common areas of the house. Probably increase at least 1 size on all of those supply runs.
And move the other 2 bedrooms to the same zone as your master suite, and rerun that supply trunk as a 14".
With that undersized return, your system definitely isn't moving 1200CFM.
Look at the amount of supply you have going to your master suite. And how much return is ran to it.
Increase your 12X12 to a 14X20 grille and run a 12" to it. And increase your 14X20 to a 14X25, and run a 16" to it.
I use a diagonal cutter/pliers.
Have you even checked for prices for materials? I'm assuming you are going to do the work yourself. Upgrading each and every flex line entails:
-Replacement of flex for each supply line and return line
-Replacement of tap at distribution box
-Replacement of boot (some boots you can just change the tap; most new construction installs do not have these)
-Boots usually come in these configurations:
-If you plan on replacing the boot sizes, you will also need to replace the grills/registers. If you keep the same size boots and are just changing out the collars, you will not have this expense. You can buy boots with duct board backs (add tap to it) or with different size collars.
-Paduit straps and foil tape
-Thermostat wiring (you will have to run thermostat wire to each thermostat and to each damper to a centralized location. You will also need to run wire from the air handler to this location.
-Barometric damper with duct (includes flex and taps)
-You would still need some duct modifications to make the system work properly.
Those are the things that I can think of off the top of my head. Also, most duct sizes are not sized to a .05 static pressure. I have been into a lot of attics and have not seen one that was sized to those standards. We have over 100,000 homes in my area and customers are unaware of the problem. Even if all the ducts were changed out, I bet most would not even notice a difference (I'm not referring to grossly undersized systems). It is just one of those things. People seem to forget about heating and air conditioning until it fails. I'm not saying it doesn't matter; I'm just letting you know how the majority of the units are currently running.
More reasonable/realistic duct sizing would be as follows:
4in 40 cfm
5in 65 cfm
6in 110 cfm
7in 160 cfm
8in 200 to 220
10in 400 cfm
12in 700 cfm
14in 1000 cfm
This is how most units are sized in our area and there are no complaints. I have seen ducts sized way below this standard and people do not realize it. That doesn't mean there aren't problems associated with it, but I have seen systems last 20 plus years with undersized ducts. I know that there is more to it than longevity, but I do not care to get into specifics right now. My point is to just show you how most systems are run and operated (not the ideal perfect situation).
Based on these numbers, you are closer to these cfm ratings. I'm not saying you are actually getting these numbers currently. No one can tell without testing.
Two 4" 80 cfm
Three 6" 330 cfm
Five 6" 550 cfm
One 7" 160 cfm
One 4" 40 cfm
Total 1160 cfm
400 cfm per ton = 1200 for 3 ton system
From these numbers, you can see that your system was designed using more moderate sizes. It is your house and you can do whatever you want to do, but I don't think your problem is significant to take drastic measures. You can upgrade the entire system, but I can almost guarantee you will be the only one in the entire neighborhood with those size ducts.
Here are my suggestions:
You are obviously getting too much air into your master suite. Unless your master suite is comparatively larger than the rest of your house, it is a safe assumption that it doesn't need that much air. I would go around the house and check temperatures looking for hot spots. You should increase air flow to these areas. You can accomplish this by increasing the duct size or adding a supply to it if there is a significant difference in temperature. Install a 10in damper into the bedroom supply line. Since you are the home owner, you can adjust the damper manually until it matches the rest of the house. I didn't mean for this post to be so long, but I feel like people tend to do too much with projects. People that help others on the internet are passionate about what they do and inform them according. I just try to give real world approaches to solutions, and I'm definitely price conscious. I sought help doing a roofing project on another forum and spent $600 to $700 more because the standards on the internet are so much higher. I even talked a professional roofer and he asked me why I went through the additional steps and expense. If I had to do it all over again, I would just install the roof like all the other companies in my area do. Good luck
Trashed all non pertinent post to the OP.
If you want to post similar posts as you did. Start a new thread in off topic forum.
Just in case you have been on vacation or something, I wanted to add some of my suggestions that were deleted. I hope that is all right beenthere. A lot of my posts were deleted that were directed to the OP. They had some of other stuff in them as well, but I think, my opinion, they could be beneficial. I will keep it short and to the point. OP you should check for temperature differences in all the rooms. Your original installer obviously didn't size your ducts correctly. They allocated over 1/3 of the air flow to your master suite. In my opinion, this is too much air flow. I have never seen a master suite that was that disproportionate to the rest of the house. They also seemed to just add six inch ducts to every large room. I've seen contractors do this just to keep cost and stock down. They do not have to stock as many sizes. Your house may require more air flow to certain areas and less to others. For example, you might need more air flow to the living room and less to the master suite. You should figure out which areas require more air flow than others. Basically, you are looking for temperature differences. This will not tell you exactly how much air flow is required for each room. You would need a contractor to determine exactly how the proper air distribution needs to be laid out. Since you need to increase air flow to your main house anyways, it makes sense to even out the temperature now while doing so. If you have temperature differences in you main house now, you will still have them if you increase all of the ducts proportionally. I hope this makes sense. Good luck with your project. If you are knowledgeable in other areas outside of HVAC, try to give back and respond to some of my questions or others on different subforums.
Thanks to both of you for responding to this thread by the way. I would have responded earlier but work has been extremely busy for me lately and unfortunately I have had very little free time.
Nonetheless, I do appreciate your suggestions. One thing I realized today, I told you incorrectly what one of my returns is. The one with the 14" flex is actually connected to a 20x20 grill. How I got 14x20, I have no idea. Does that make any difference at all or do you still recommend that I bump the flex duct up to 16"?
Pomelo, by the way, earlier I was not ignoring your advice and I apologize if anything I said or did not say indicated that. I actually do think the 10" damper is a good place to start. To your point about hot points in the house, today was a good test for that since we have today was about 85 in NC. Anyways, the "hot" room in the house is the sunroom. There are two vents in there that I believe are connected by a 6" flex each. One consideration is just adding another vent there. Or to beenthere's point, I might just need to increase the ducts to 7" coming off the 14" trunkline. Still at the end of the day, the master suite is getting way to much airflow, so the 10" damper is a good idea. I was a little spooked at the idea because I just had our blower motor replaced a few weeks. I was concerned the excess static pressure might cause some harm. However, I am a complete newbie at this, so I could be completely wrong.
A little off topic
By the way, this is a little off topic I know, but.... one thing I have never liked is how the 14" flex trunkline makes a very sharp 90 degree turn right off the plenum. Plus, the flex is not stretched at all. I always thought this hampered airflow through out the rest of the house. Personally (this may be overkill), I would rather just replace the trunkline with a round metal 14". In it's current state, the flex connects to a rectangular "distribution" box. I would like to get away from that. But.. how do you connect supply lines to a round metal trunk? The only thing I could surmise would be to use a saddle duct tap such as this.
Would that work? Or is there some better way? Also, is there any benefit to replacing the this flex run with a round metal?
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