Need opinions on AC issue

[matemike]

I have a 32 year old 2 story house that is 2650sq ft, located in hot coastal-bend Texas. We have lived here since 2018. The house is equipped with a single 5-ton HVAC unit, blower located in the upstairs over head attic space. That single unit is asked to heat and cool the whole house, which it does OKAY at best. The upstairs rooms (3 bedrooms, and a play room) get good ac and heat all year round. The downstairs living room, dining room and kitchen areas do okay as well. But our downstairs master bedroom, master bathroom, and utility room are down right HOT in the summer. We can’t get them below 78 deg F on a good day; usually more like 80 F. Those few rooms are also cold in the winter. The 5 vents covering those spaces are at the end of the line from the air handler unit. In fact, it is a single 14” duct line that comes from the unit to a box in the attic over the master bed room; that then splays off to those 5 vents. The vents get air flow, but not much, and the temp is not very useful by the time it does get there.

I’ve gotten two opinions now, still waiting on actuall quotes. But one AC company in town says to add a little 1.5 ton unit and run those 5 vents in the master bed and bath room and utility room and add a vent to the toilet room. This would require a new compressor, condenser, electrical, copper and of course an intake and thermostat. Then they would cap off that 14” line at the existing 5 ton unit. I’ve got a bathroom upstairs that could use two new vents (there are currently none) and add a vent in the play room to have running off the existing 5 ton unit.

The second opinion said to add “zoning” to my single 5 ton unit and a variable speed fan to keep areas at proper temps separately and more efficiently throughout the day and night. The 5 ton unit is well capable of this. I suppose they would just add some louvers in the attic to different zones and another thermostat upstairs and hopefully a thermostat in our master bed room area. I still want to add vents to our master toilet area and two in the upstairs bathroom that currently have no vents. Those little spaces get HOT in the summer when the doors are closed .

No matter what route we go, we have a guy lined up to come blow in more insulation in the two attic spaces, put radiant barrier in the overhead of the attics and check that my current insulation bats are not impeding the vents in the roof eves so we are getting proper air flow throughout the attics.

I fear if we add the 1.5t unit that the 5 ton could be oversized for 1800 sq ft of space .

And I fear that if we go with the zoning only that we won’t get what we were completely wanting to achieve. Kind of a band-aid approach.

AC experts, what would you do?

 

[yatg]

How old is the existing 5ton?

 

[fitter30]

Two story houses need two separate units. I'm not a fan of zoning one unit except with a variable refrigerate flow and air flow. 5 ton unit for 1800' is probably over size but with a smaller unit it could be used for help with lowering the humidity. Humidity flow from high to low just like temperature. Wait for adding insulation till the equipment is added or changed. It would be a nightmare to work around and get smashed down.
There are fed tax credits, possible state and the electric company might have something. Check with the electric company see if they offer a energy audit with a blower door test there could be more rebates offered.

 

[matemike]

How old is the existing 5ton?

Installed 2008

Edited: Man, 15 years sneaks up on ya quick!

 

[462867aa]

Was recently in a similar situation. 5 ton unit that just didn't seem to work great. The problem was the ducting installation. Installed metal ducts in place of the flex duct. Can't believe the difference it made.

 

[matemike]

Two story houses need two separate units. I'm not a fan of zoning one unit except with a variable refrigerate flow and air flow.

I’m making sure this is for variable speed on the fan and Freon flow. I think it was just a variable speed fan.

5 ton unit for 1800' is probably over size but with a smaller unit it could be used for help with lowering the humidity. Humidity flow from high to low just like temperature.

Wait for adding insulation till the equipment is added or changed. It would be a nightmare to work around and get smashed down.

Yes, that is the sure plan.

There are fed tax credits, possible state and the electric company might have something. Check with the electric company see if they offer a energy audit with a blower door test there could be more rebates offered.

Rebates included and explained in the quote. But thanks for pointing that out.

 

[danski0224]

I have a 32 year old 2 story house that is 2650sq ft, located in hot coastal-bend Texas. We have lived here since 2018. The house is equipped with a single 5-ton HVAC unit, blower located in the upstairs over head attic space. That single unit is asked to heat and cool the whole house, which it does OKAY at best. The upstairs rooms (3 bedrooms, and a play room) get good ac and heat all year round. The downstairs living room, dining room and kitchen areas do okay as well. But our downstairs master bedroom, master bathroom, and utility room are down right HOT in the summer. We can’t get them below 78 deg F on a good day; usually more like 80 F. Those few rooms are also cold in the winter. The 5 vents covering those spaces are at the end of the line from the air handler unit. In fact, it is a single 14” duct line that comes from the unit to a box in the attic over the master bed room; that then splays off to those 5 vents. The vents get air flow, but not much, and the temp is not very useful by the time it does get there.

I’ve gotten two opinions now, still waiting on actuall quotes. But one AC company in town says to add a little 1.5 ton unit and run those 5 vents in the master bed and bath room and utility room and add a vent to the toilet room. This would require a new compressor, condenser, electrical, copper and of course an intake and thermostat. Then they would cap off that 14” line at the existing 5 ton unit. I’ve got a bathroom upstairs that could use two new vents (there are currently none) and add a vent in the play room to have running off the existing 5 ton unit.

The second opinion said to add “zoning” to my single 5 ton unit and a variable speed fan to keep areas at proper temps separately and more efficiently throughout the day and night. The 5 ton unit is well capable of this. I suppose they would just add some louvers in the attic to different zones and another thermostat upstairs and hopefully a thermostat in our master bed room area. I still want to add vents to our master toilet area and two in the upstairs bathroom that currently have no vents. Those little spaces get HOT in the summer when the doors are closed .

No matter what route we go, we have a guy lined up to come blow in more insulation in the two attic spaces, put radiant barrier in the overhead of the attics and check that my current insulation bats are not impeding the vents in the roof eves so we are getting proper air flow throughout the attics.

I fear if we add the 1.5t unit that the 5 ton could be oversized for 1800 sq ft of space .

And I fear that if we go with the zoning only that we won’t get what we were completely wanting to achieve. Kind of a band-aid approach.

AC experts, what would you do?

I have yet to see a "5 ton" system in the wild that is installed properly, as in there is enough ductwork to move the required amount of airflow. Most have had barely enough ductwork to handle 3 or 3.5 tons of airflow, much less 5. Not only is duct size important, how it is made and connected is important. Properly sized duct can be killed with ****** design and installation (bad airflow).

Typical residential zoning does not work. Don't do it. Just don't.

Your number one existing installation problem is the fact that the equipment and ductwork is in the attic. The duct insulation might be classified as "R8" if you are lucky, but it will not be delivering that in the "as-installed" condition. If R8 isn't good enough for the attic, then why would anyone think it is good enough for the ductwork? There can easily be a 100 degree temperature difference between the air in the ductwork and the air in the attic.

Next, I bet that the ductwork (or rather, flex connections) are not sealed, nor are the register boots in the ceiling. Duct leakage in an attic will absolutely kill performance. It is not unusual to see duct systems with 20%-30% leakage.

You need to seriously look at spray foaming the attic, making it conditioned space.

Whatever is done with insulation (spray foam or not), that needs to be factored into any new system designs.

If you want it to work when the repairs are done...

You need to find someone competent to perform a system evaluation and load calculation, then come up with a plan.

Factoring in insulation changes, a room by room load calculation needs to be performed.

Given a room by room load, then the ductwork can be designed.

Then the equipment can be selected. Do be aware that there are at least 2 different "5 ton" evaporator coils available from most manufacturers, and only one will actually deliver close to the rated capacity (and it costs about 2x the other one). There is a lot that goes into selecting the proper matched equipment.

In the trade, this is Manual J, Manual D and Manual S.

There is software called HVAC-Calc that can do the load calculation and duct sizing. You will need to know something about the basics to use the duct sizing feature. It is not ACCA approved, but it does work. A single use license is about $50.00 and it is relatively easy to do the load calculation part.

Adding another unit is a band aid.

I have typed responses like this before, and I do not think that anyone has actually gone through and fixed the problems correctly.

Good luck.

 

[matemike]

Was recently in a similar situation. 5 ton unit that just didn't seem to work great. The problem was the ducting installation. Installed metal ducts in place of the flex duct. Can't believe the difference it made.

Good to know. However, I am immediately reminded that my wife's grandparents house in Baton Rouge, Louisiana had metal ducts, and you could hear people talking, not just room to room, but all though the house through the duct work. Do you notice that?

 

[matemike]

A little more info:


The initial A/C company that suggested to add the 1.5T unit quoted back that their cost would be $7,700, but not factored in electrical work yet. When asked about the humidity issue with the 5T unit cooling less space they said, ya, you might get humidity and mold, but then we'd just change that out for a 4 T unit and I'd just be shelling out more money.


I got the quotes back from the second company for a couple different options for "zoning" units. The guy told me that his options to get "zoning" is a win win because it not only works better than adding a second small unit, but it is cheaper too. I thought all I was going to get was new hi-tech louvers installed on my existing unit's outlets and thermostats in a couple places to automatically control those louvers....right? wrong.
Turns out this project is a complete replacement of my entire existing A/C unit. Holy Cow! Not what I was thinking/wanting. Therefore I was not expecting $27,000.
He went on in the quote to tell me that adding a 1.5T unit would be about $9,000. But he won't do that for me because it's not the right way, unless he changed out the 5T for a 3.5T as well. Another $10,000.


Getting my ducts investigated, attached properly and made of better material is understood. But I am not understanding how to get my attic completely foam sealed. A couple people who looked at it said that I'd have to remove all the ridge vents and eve vents, get it completely sealed, then still probably have sweating issues between the foam and the wood boards. Sounds like foam insulation needs to be applied on new builds, and that this house is not a candidate...? So I'm also not understanding, but I don't think my attics can be "conditioned" spaces.


So between the two bad choices, what's a better choice? zoning, or adding a smaller unit?

 

[CADPoint]

You can see where that 5 ton sits in real life with your existing structure.

https://www.hunker.com/13407289/how-to-calculate-hvac-tonnage

At least check to see what you have verses what you think you need and not negating all
the other fine aspects presented here or in real life (the bid) - verses the joy of ownership.

 

[danski0224]

So between the two bad choices, what's a better choice? zoning, or adding a smaller unit?

Number 3, fixing it properly.

 

[PoorUB]

Have you looked over the existing system? Is the duct work in good shape and properly insulated?

If it were me I would look over what you have, study up and make sure what you have is correct before moving on. I worked in HVAC for years and it seems to me most companies just want to sell new equipment and not fix the existing. The typical HVAC tech is not wantng to swim around in your attic and make sure the ducts are in good shape and insulated properly.

If nothing else being more knowledgeable is a good thing when the HVAC contractor wants to sell you something.

On the other hand I can not see a down side with putting a 18,000 BTU unit in your master bedroom and leaving the rest alone. I doubt it will affect the rest of the house that much.

Can you change the duct work coming off the main unit? That may be all you need. Increase the size, add another duct run, get more air flow. I know in my house I added a couple 6" runs to the south end of the house and a 4" run in the basement and it made a world of difference. The main floor in hot days might be 10 degrees warmer than the lower floor, now it usually is right on.

 

[462867aa]

Good to know. However, I am immediately reminded that my wife's grandparents house in Baton Rouge, Louisiana had metal ducts, and you could hear people talking, not just room to room, but all though the house through the duct work. Do you notice that?

 

[462867aa]

When I replaced the ducts the only thing I noticed was a small increase in air noise when running. Absolutely no sound transmission from other rooms. The bit of extra air noise was a small price to pay for the increased performance.

 

[matemike]

On the other hand I can not see a down side with putting a 18,000 BTU unit in your master bedroom and leaving the rest alone. I doubt it will affect the rest of the house that much.

Can you change the duct work coming off the main unit? That may be all you need. Increase the size, add another duct run, get more air flow.

So if I added a little 1.5T unit to the master areas, I would cut those areas off the main. You say 18,000 BTU’s. How does that compare to 1.5T. Same?

I am adding a duct in the master area to be run of possibly new extra little unit and adding three little ducts upstairs that will run off the main unit.

I think I do need my duct work looked over by a company that does that. So far both folks who looked over my system wants to do exactly what you said, sell me and add a new or additional system.

 

[matemike]

IMO, my duct work does seem to be sealed up good, but as always, some kinks and probably no a high R value.

 

[PoorUB]

So if I added a little 1.5T unit to the master areas, I would cut those areas off the main. You say 18,000 BTU’s. How does that compare to 1.5T. Same?

I am adding a duct in the master area to be run of possibly new extra little unit and adding three little ducts upstairs that will run off the main unit.

I think I do need my duct work looked over by a company that does that. So far both folks who looked over my system wants to do exactly what you said, sell me and add a new or additional system.

12,000 BTU per ton so 18,000 BTU = 1.5 ton. Some guys like tons, some guys like BTU. either works.

From your pictures your duct work looks to be in good condition, but often installers think six inch is all they need and it is often too small for the room size.

When I sized ducts for residential I always used 1 CFM per square foot. It will be oversized, but it is a lot simpler to choke back a register than to try replace the too small duct.

Also flex duct cuts flow by around 40%. So with a six inch round metal duct you will get pretty close to 100 CFM and with six inch flex you will get about 60 CFM. Many installers do not account for the reduction of air flow with flex. Other than a very small room, like a bathroom nobody should use six inch flex in typical home but they do it all the time and then the home owner complains that areas of the home do not heat of cool.

Increasing the duct size to your bedroom area might be all you need to do assuming the equipment can keep up wit the total load, but it is probably all but impossible to replace the duct without tearing out walls.

Also keep in mind the ducts work if you add a unit. 1.5 tons needs 600 CFM so six or more six inch runs, more or larger diameter with flex.

Even my own home on the south end was warm all year around with the solar gain. My living room had two duct runs, both six inch so maybe 100 CFM, except the registers were good for maybe 80 CFM. The living room is close to 300 sqft, so 300 CFM and it was getting maybe 160 CFM. I added anothe six inch duct and, plus one in the kitchen and that end of the house is the same temp as the rest of the house. The living room is still short with using 1 CFM per sqft, but is is doing fine with roughly 240 CFM.

 

[danski0224]

Ugh.

There's no way that there's enough ductwork to support 5 tons of airflow.

 

[jkuro]

Ok you have 5 supply ducts, now do you have 5 return ducts? You won't get much air supply, CFM, into the rooms, without a proper return.

 

[RoninB4]

I have typed responses like this before, and I do not think that anyone has actually gone through and fixed the problems correctly.

-I did after getting a quote of $29,000 from a company with great reviews. I did all the calculations in manuals J, D, and S. They do require a lot of data/time, they are worth doing even if it's just to know if you're being taken for a fool. Taking advice from people trying to sell you things is seldom a good approach, especially when it involves high price tags. There's a lot of questionable practices, under-skilled workers, and borderline fraud in the HVAC industry in this area. Many don't even bother with load/flow calculations, preferring to do a simple replacement and/or addition without analyzing your particular conditions.

I'd start with doing more than just looking/photographing your ducting, do the math to determine if it's even flowing air properly, is sealed properly, and isn't restricted/pinched. The ducting in my 13 year old house was poorly executed but I didn't know this until I started doing the calculations and inspecting it. I installed the 4 ton unit myself last November and am still working through the ducting/insulation issues the original installers hacked in. I knew nothing about HVAC when I started this either.

All apologies to the honest, conscientious HVAC workers out there for some of my remarks. Had any of you been in the area I wouldn't still be working on this project.

 

[PoorUB]

Ugh.

There's no way that there's enough ductwork to support 5 tons of airflow.

You are probably correct, but it is hard to tell the size of the duct with a picture.

-I did after getting a quote of $29,000 from a company with great reviews. I did all the calculations in manuals J, D, and S. They do require a lot of data/time, they are worth doing even if it's just to know if you're being taken for a fool. Taking advice from people trying to sell you things is seldom a good approach, especially when it involves high price tags. There's a lot of questionable practices, under-skilled workers, and borderline fraud in the HVAC industry in this area. Many don't even bother with load/flow calculations, preferring to do a simple replacement and/or addition without analyzing your particular conditions.

I'd start with doing more than just looking/photographing your ducting, do the math to determine if it's even flowing air properly, is sealed properly, and isn't restricted/pinched. The ducting in my 13 year old house was poorly executed but I didn't know this until I started doing the calculations and inspecting it. I installed the 4 ton unit myself last November and am still working through the ducting/insulation issues the original installers hacked in. I knew nothing about HVAC when I started this either.

All apologies to the honest, conscientious HVAC workers out there for some of my remarks. Had any of you been in the area I wouldn't still be working on this project.

Between unskilled workers, general contractors trying to build to a price point and homeowners that will not spend the money to do it properly it just snow balls.

I have a good friend that had an HVAC company. He took me through a house they were doing. I made some comment about the duct work being inadequate and he told me they have to do it that way to get the job. I looked at him and asked, "So you knowingly undersized all the dict work?" Yep, "if we would don't it they will hire someone that will." this guy probably did 100 houses a year. all built short on duct. This is one of the reasons I avoid tract homes, everything is built just about good enough. My wife and i looked at buying a different home a few years back. I finally gave up it was so frustrating to so houses so poorly built. I feel sorry for people that buy a new home with no clue what they are looking at.

I had a good friend buy a $325,000 house in Missouri. It was a custom built home. At the time you could buy a nice home for that dollar amount. In our area it would have been a $500K home, pre-COVID dollars. He has been fixing short comings in the HVAC and the general construction ever since. Luckily he has found a good HVAC contractor and they have come to and understanding on getting things done right and not to a price point.

 

[danski0224]

You are probably correct, but it is hard to tell the size of the duct with a picture.

Not really.

6" flex is roughly 8" across, duct is the same size as the furnace, and the ducts are jammed together.

Whether it's 6 or 8, not enough.