"The plenum is NOT insulated inside (according to the installation HVAC folks) or outside in anyway, and neither is the ducts. They are sheet metal."

And there is your problem.

The only way it won't sweat is if it never gets below dewpoint.

 

Thank you for the reply.

What should have happened for a proper installation? Should the inside of the plenum have been insulated somehow? or the outside of the plenum, and with what type of material?

For a corrective measures should they take the duct work apart and insulate the inside for the first few feet, or just insulate the outside somehow for a few feet. Hmm the zone damper condenses too coming out one of the main branches.

The HVAC installation folks looked me straight in the eye and said that noone EVER insulates plenums when I asked him. Guess I can't trust them.

Should the sheet metal plenum, and all of the sheet metal branches coming out the plenum, have been insulated everywhere? Or just the first few feet of run?

I live in Iowa in case anyone needs to know the climate I live in (snow in the winter/hot in the summer)

Thanks for your help everyone.

 

also I was wondering, can this situation create a mold problem inside on the ducts (maybe it is condensing inside also?, or only on the outside and I just have to put up with a mess. Or possibly can equipment replacement early on?

my wife runs a preschool in our finished basement where the furnace/ac is located

 

You can sometimes get away with not insulating the ducts in well insulated and conditioned areas of the home. I believe the plenums should always be insulated and any ducts when installed in any mechanical room. I would have them wrap the outside of the plenum and ducts in that room. May look better if insulated with a duct/fiberboard on the inside but good luck getting them to tear into it now.

Do you notice a temperature difference in that room than the others? They may be able to give that area a little more supply and do without insulating.

 

Hmm my zone system used to have a "pressure relief" duct with a door in it that bleed off extra pressure, if only one zone was turned on. This pressure relief duct releases extra pressure (cold air) itself in the mechanical room just into the empty space. It was condensing this summer in the mechanical room )on the outside of the plenum and ducts) and it would get really cold in there.

I had them add this "pressure relief" duct back into the actual return air before the air filter (that is what it said to do in the zone manual), and that solved it getting extra cold in the room. But the ducts and plenum still condense unfortunately.

 

The plenum sweating and creating a mess is unacceptable in any case and even more so in a finished room. The plenum will rust out early if continued sweating occurs. I don't know about the statement that no one insulates ducts and plenums. I would call him on it. You always insulate ducts and plenums in un-conditioned areas like in attics and crawl spaces and in areas that may not be well insulated and sealed.

I would call and speak with the owner and demand the problem be fixed or he will be held responsible for any accidents or damage caused by the condensation on the floors.

 

Thank you for your help RCB, I really appreciate it. This will cause my wife and I a lot less headaches...

Whew I am so glad I found this board, and feel privileged to receive help from you.

Thanks for the explanations and for making this simple! :cheers:

 

I am not completely familiar of how things are done in your area. Most all of the systems supply side here is insulated through the entire home. Someone with plenty of experience with your install situation should be along shortly that will be able to give you better help than I can provide on this one.

I would suggest having them resolve the issues as it is their job and you didn't pay for a system that you have to mop up after daily. You need to keep calling them on this until it is fixed before the warranty gets outdated.

 

You said the company has been out three times looking it over so I didn't mention the air flow, charge or dirty evaporator coil but either of these can cause the supply to run colder than designed which will aid in causing the plenum and duct condensing.

You also mentioned that two zones are often shut. Were they closed when they came out and did they check the CFM during that situation? Might want to consider proper ventilation for that room as well. If you are having poor air recirculation there the system can't dehumidify it, just forcing cold air in doesn't work.

Hope you get it sorted. It's pretty late but someone may come along later with better insight on the issue.

 

Insultating the first few feet only moves the condensate further down the ducts. What is the temp/%RH in the space? What is the temp of air in the ducts?Maintaining <50%RH in the basement space is important avoid mold and condensation on ducts.
Get a good temp/%RH monitor and check your home throughout.
Keep us posted.
Regards tB

 

You need to get that plenum insulated with fiberglass for sure. Thats the only way it will stop sweating. I can;t believe the contractor doesn't even know that. That is sad. Also ask them to check the airflow is setup properly per tonnage for your AC unit.

 

In the midwest & Ohio Valley that I'm familiar with, supply work in a basement is not insulated. If it is so humid there that the ductwork sweats, it is too humid period. You should get good (www.thermastor.com) dehumidifier to prevent mold other places in the basement.

Ducts in any unconditioned space like a garage or attic certainly should be insulated.

 

Okay, everyone I have some further research today it got above 90 degrees outside which brings on the condensation problems on the outside of the ducts.

The outside of the plenum is still condensing , and the branch off the plenum (zone) that goes up a unconditioned flu chase up to the attic (for the upstairs heating/cooling) is dripping water down the chase off the ducts.

But there seems to be a much bigger problem. These sheet metal ducts going up the flu chase are not insulated in any way. This flu chase leads up to the attic. The stud walls of the flu chase are insulated with R-22 and R-13 on one side but it is not conditioned air in this flu chase. There is water dripping down the ducts from the flu chase I can see it with a flash light looking up from the mechanical room. That is the main problem is that this water dripping out the flu cahse is leaving a large pool of water on the floor of the mechanical room. Also the plenum and the whole branch coming off the plenum is condensing, but not as bad as the flu chase

All ducts in this entire branch going up the flu chase into the attic are uninsulated according to contractor. Earlier this summer the contractors went into the attic and put fiberglass insulation on the big box in the attic that has insulated flex ducts leading off it. Before this big box only had blown attic insulation covering it and they thought that was the problem. Supposedly they also made sure that where the flu chase ducts and the attic meets, is a tight seal now. The manager also told me the contractor that installed everything last year is no longer with the company.

I did what you guys suggested and bought a hygrometer today. Relative Humidity in the mechanical room is 65 with a dehumidifier turned off today, at a temperature in the mechacial room of 70 degrees.

I am feeling like yes maybe the dehumidifier will help the mechanical room I guess if I run it 24/7, but should I really be expected to do this? Also I wondering with the flu chase dripping problems coming to light I don't think there is anyway to dehumidify up in there for two stories.

Thanks for you help everyone. In my opinion does it seem like the plenum, all the way up the zone branch that leads into the attic through the flu chase, should have been insulated?

What type of easy fixes is there? or basically does someone need to tear the sheetrock walls up and tear out that entire branch and start over with insulated ductwork?

Thanks again everyone for your expert help.

 

My opinion is that the chase section should have been insulated since it receives no air circulation. Is it possible that the chase is open to the attic area? Simply throwing insulation over the penetration isn't sufficient. It should have been foam filled or drywall and silicone then covered with insulation at the attic penetration.

65%RH is too high in that mechanical room. As Teddy Bear stated you should be at 50% or close to it.

Is there any return in or near the mechanical room? If there isn't one in the room is there any way for the air in that room to reach the closest return?

 

hmm I would have to climb up into the attic and dig through r-50 to look, but "supposedly" the attic chase is sealed from the attic I believe by one of those 1 inch think pink r-10 styrofoam sheets or whatever it is, with r-50 blown insulation on top of it.

The mechanical room does have a register that reaches into the next room, where ambiant air from the next room can freely enter. So the air flow is not sealed tight in there or anything.

I know the contractors did some work up there when they came back to the job site, so I am not entirely sure how it is sealed now. Definately is not foam filled.

I wonder if there would be a process where we could foam fill the entire chase, if that would take care of the problem. Or maybe the insulation folks wouldn't have a way to foam fill the chase entirely since the chase is two stories tall.

I'll get the dehumidifier started again in the mechanical room tonight. Thanks RH 50 it is in there. Unfortunately the weather is suppose to cool off now over the next several days over the next 5 days, so there won't be any condensation problems to report now until the temp gets above 90 degrees outside again.

I believe the attic is the chase entering the attic is properly sealed. But without air flow in the chase and no duct insulation, I think it is just making it drip.... I suppose this could setup for mold problems and rusting out of the ducts over the long term.

Maybe spray foam would be an option? The only other option is to tear out the walls of the flu chase and the entire trunk and start over maybe?

I thought about having someone add vent registers (like on the return air) mounted into the wall so that ambiant air from the main floors could reach the flu chase. I don't know if that would solve the problem though

 

Probably the only feasible way of insulating the duct in the chase would be to seal off the bottom and drop in the blow in insulation material and hope for a complete fill with no gaps that might still sweat causing wet insulation. If the duct is sweating in the chase there is good possibility it could cause a mold problem sooner or later.

Before going to all of this effort and expense I would highly recommend calling in a reputable outside contractor to evaluate the system for a second opinion at this point. No sense in trial and error if it is something that can be adjusted within the system itself that the installing company is overlooking. I would hate to see you throwing money away trying to compensate for an improper running system that may be remedied with a few adjustments.

 

Time to take a step back. Understand what is going on before rushing to band aid fixes.

You have high humidity in your basement. Thats not the hvac guys fault. What is the source?

You have chases tuning basement to attic. If they are not airtight that is a big problem.

Is this an energy star rated home? If so, find out who the rater was and start turning the heat up under their feet. If not, get an energy audit and get a handle on the homes deficiencies. Not the symptoms, the deficiencies.

Non communicating zoning is adding to your troubles. Bypass damper returning cold air. Oversized equipment running too cold. (People don't believe they should downsize zoned systems need to read your thread) Too much leakage to outside keeping humidity levels high. Dirty coil slowing airflow. Duct work running up into an unconditioned attic! Your list of potential issues is long and solutions likely incremental rather than one "fix all".

 

Although I can agree with the bulk of your post I would have to disagree with the contractor not being at fault. It is their job to install the equipment appropriately for the surrounding conditions. Not for the homeowner to alter or adjust the condition of the home to suit the installers job despite if it may be in the owners best interests.

 

If your bad suspension causes the tires I sell you to wear out prematurely, don't look to me for new tires.

If you are not careful, and get a handle on all the interconnected issues, by the time you get a cohesive strategy to address the situation you'll have burned the patience of the contractors.

Get a clear picture of the WHOLE problem, the best practices for solving, then take it to the contractors responsible. Calling one of the parties over and over for something they don't have complete control or responsibility for, or understanding of, is a waste of your time as well.

 

Not sure where you buy tires but my guys will look at my old tires and suspension and tell me if I need an alignment, shocks, or other suspension work to keep my new tires from wearing uneven or prematurely. That is exactly what the more reputable HVAC companies will do for the home. They should have had an audit done to insure proper replacement to begin with and thus would have known to insulate the plenum or ducts if needed or to warn the home owner of possible issues and suggestions to make that area more efficient.

Just my opinion though. I would rather install to satisfy the conditions rather than to install equipment and tell the homeowner you need to make all kinds of repairs to the home so my install won't make a mess on the floor and chases. Of which they are completely oblivious to since the owner has stated they don't know why the system is sweating to begin with. That tells me they didn't have any thoughts to the conditions or suggestions for improvement to the owner. The other way is just working backwards IMO. You are supposed to evaluate the space before you go installing things.

 

I agree, but maybe the buyer was given the option of having suspension testing done and declined, "I just want a new system."

Then what, walk away from the tire sale?

And this is a brand new home. I don't know the deal between builder and hvac guy, but I suspect the hvac guy was not charged with envelope quality control.

Again, no zip in op details (hey Dad, would be nice to require a zip or at least a State!), but many hvac guys where you are have blower doors for install crews?

 

He stated he lived in Iowa.

Maybe there was no communication between the general contractor and the HVAC company or maybe the home wasn't built exactly to spec as the plans that the HVAC company used to determine the system specs? I have no idea but there was no mention of either so we have to go by what information is given.

Several statements stand out though that may put more pressure toward installer fault or in the least negligence.

The plenum is NOT insulated inside (according to the installation HVAC folks) or outside in anyway, and neither is the ducts. They are sheet metal.

I have had the folks that installed the system take a look at it three different times, and I forked out a lot of money for an entire air conditioning / furnace system to them last year, and they have not been able to solve the issue.

All of this drips on the floor making a big mess anytime the temperature gets above 90 degrees outside. To make it worse it drips on an electrical subpanel which I am worried about as far as shock hazard.

If I am going to install a device that may in any way have a chance to condensate over an electrical panel it's getting insulated period.

The HVAC installation folks looked me straight in the eye and said that noone EVER insulates plenums

This leads me to believe the installer isn't exactly on the ball. By the third call out they should have played the I told you so card on the audit side or would have placed blame on the home's design or lack of per the homes specified building design of which they should have used to determine proper installation of equipment for the home.

I really do hate pointing the finger at any company or tech but from what I have witnessed from so called professionals is down right appalling sometimes. And not saying that all my jobs are better than anyone else or always 100% perfect but I do try to cover every base and follow every conceivable practice of doing it right. I am sure you have seen installs that you think a complete idiot could have done better. Bottom line is we do not have the whole story from both sides or pics, system pressures, stats, etc so we can only judge by what we are given here. Truth be know it could be a little of everything or none at all since we can't be there first hand. lol

 

Mid-Atlantic

Here's some perspective.
Seen/owned a few homes in Maryland and Virginia area with HVAC in the basement and and the supply/return ducts are not generally insulated. A basement (especially yours that is finished) seems to be considered "conditioned" space and is generally not subject to temp or humidity extremes. In my (and neighbors) there are return plenums running to the attic in uninsulated chases with uninsulated ducts. BUT, the minute you cross into the attic, everything is insulated.

Now you say you don't have basement humidity, but 65% is high.

My guess is that your chase is acting as a conduit for the infiltration of warm moist air from the attic into the basement utility room, raising the humidity and causing condensation on cold ductwork. Solution is to attack humidity and not ductwork.

You need to go into attic and make sure that penetration of chase/duct is very well sealed with vapor retarders such as plastic sheet/plywood/polyurethane spray foam. FIBERGLASS batts or blown-in WILL NOT stop air infiltration and unsealed kraft facing provide little help.

Start here and see what happens to your 65%.