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Heating & Air Conditioning

Pex Installed On AC Duct?

11 years ago

My HVAC contractor has installed the pex for the radiators on the A/C ducts as shown in the picture below. Is this normal? Anything that I should be aware of or should mention to the contractor? Thank you.

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Comments (16)

juliekcmo
11 years ago
So they put a hole in your duct, instead of strapping to the floor joist? I am no duct install expert, but I question that.
david_cary
11 years ago
Interesting. Around here Pex would only be on supply lines and only installed by a plumber. PVC would be used for condensate drains. No way would a plumber screw into a duct. The pex doesn't appear to be strapped at frequent enough intervals.

That uninsulated duct looks to be in unconditioned area - certainly not code.

The hole in the duct is probably well sealed by the screw but it doesn't seem ideal.
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jb I have had a similar issue and finally fixed it. I have a 3 year old home that is well insulated and tightly sealed. It is a 2 story home with a basement with geothermal heat/cooling. The second story of the home contains only guest bedrooms that are rarely used. The second floor has its own dedicated hvac and I set the stats to cover extreme temps (set temp = 60 in winter, 82 in summer). These settings cover the rare extreme temperature cases but also enure that the hvac unit doesn't normally need to run to save on heating/cooling costs. It turns out that in the winter the warm air rising from the first floor actually keeps the rooms on the second floor warm enough that I don't normally need to run the hvac unit upstairs. However, not running the hvac upstairs is what caused the condensation problem like you have. The key to the issue is that the insulted ducts for the second floor rooms run throughout the attic. Even though the ducts are insulated and my attic is over insulated, the air and surfaces inside the ducts will get very cold if the hvac is left off. When the warm air rising from the first floor gets into the duct inlets a lot of condensation forms. But I notcied that the condensation only formed when the outside temps fell below about 20 degrees. The first time this happened, I soaked up the water on the carpet and then turned on the heat and everything dried up. I also noticed that as long as I ran the heat up there I did not get condensation even when the temps outside dropped to zero. I figured out that as long as I kept warm air moving through the ducts that the condensation would not form. But I did not want to run the hvac up there all winter because it is a waste of money. I had an idea that whenever the temps dropped below 25, I went upstairs and turned on the hvac fan but left the heat off. The idea was that continuously moving the warm air from the second floor rooms (which naturally get heat from the first floor) through the attic ducts would be enough to keep the inside of those ducts warm enough to not create the condition for condensation to form. This process proved to work for me but was a bit of a pain. I had to always remember to go up and turn the fan on at night and then shut the fan off in the morning. But it worked. AFter one season on manually turning the hvac fan upstairs on and off I decided to automate the system. Since I have a zoning up there, I checked the manual for my zone contoller (EWC Controls Ultra Zone 4) and found out that is has a dry contact input for a carbon monoxcide sensor. This feature allows the automatic detection of CO (with a seperate CO sensor) and allows the hvac fan and a freash air inlet to be automatically turned on to circulate fresh air through the system. I used that CO dry contact input to hook up a battery operated progammable timer with a dry contact closure so that every night at 6pm the hvac fan turns on, and every morning at 6am the fan turns off. I only turn this timer on during the months when nightime temps drop below 25 (generally Jan & Feb). This fixed my problem and saved me the hastle of doing it manually. When this problem first surfaced I thought about sealing up the registers upstairs but decided against that approach becuase there are times when I do run the hvac (when we have guests or when it is really cold outside) and so I would have to run up there and take the seals off. There are quite a few regsiters and it just wasn't a practical solution even though it probably would have worked. The challenge is making sure that the seals are air tight.
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The apparent contradiction of cooling inadequacy vs. heating sufficiency is not a contradiction at all. It is basic physics and it can not be messed with. If you have the heat transfer rates and capacities/contributions of both heating and cooling appliances arithmetic will make sense of it. I specify contribution because you need to know if they are operating up to their rated capacity. Condition of the ducts also contributes, to both heating and cooling as you pointed out. Of course, and the calculations involving existing construction vs. new construction is sometimes challenging due to unknowns in the old stuff. Rather than estimates of heat transfer using assumptions about the construction, you can do better with fuel use rates. You should be able to get real heat contribution from the furnace and fuel use records (and heating degree days) from the coldest weeks of the year when space heating makes hot water and cooking insignificant. You also need to know the efficiency of the furnace. An energy rater or engineer should be able to use that data to calculate the heat transfer rates of the structure. (BTU in must equal BTU out.) Those rates can also be used for heat transfer in the other direction in the summer. Those calculations can be done today. You have fuel use records and you can get degree days from a nearby weather station. It is somewhat less common to use energy use of the cooling appliance for estimates, but it should work just as well. You need to separate electricity use by installing a separate meter and the contribution of humidity removal will have to be factored in. That means that you'd have to record humidity inside and outside and include that in the calculation. It is likely that you have sufficient capacity for you furnace or it is oversized whereas the cooling capacity is not adequate if your cooling unit is functioning properly. Again, calculations will tell you. How do you fix it? Better insulation on the ducts, structure envelope and better sealing of both will always cost less in the long run than installing a larger appliance. Bringing the ducts indoors is also a good idea as pointed out by mike_home. Don't think of active fans if you consider better attic ventilation. It needs to be passive. it is difficult, however, to draw enough air through an attic to make much of a difference in its temperature. Most of the heat transfer into the living space is due to re-radiation of heat from the underside of the roof deck. That is why radiation barriers were so "hot" for a time. The trouble with them is that they get dirty and lose effectiveness pretty quickly. It was a nice idea, but did not work as expected.
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big_al_41
11 years ago
Also .. and I'm no expert .. but it seems that they moved the duct from about 2 feet away to it's present position ( right to left ) and just used metal foil tape to cover the original hole .. I don't think that will stand up to the test of time
energy_rater_la
11 years ago
these are questions to ask hvac installer
plumber & possibly builder.

not enough info for us to make the call.

best of luck.
david_cary
11 years ago
I bet there is a metal cover plate and then tape to hold it on.
countryboymo
11 years ago
Unless the tape is mastic tape it is worthless. The pex job is half donkeyed. If any of the screws in the sheetmetal of the duct holding the pex got stripped the expansion and contraction will eventually pull the screws out and after one pulls out the extra weight on the other will pull it. Make the installer fix it and screw it to the wood or someone else might be doing it later. A water leak could be involved in this mess also if not corrected as the metal clips wear on the pex which are probably for metal conduit.
energy_rater_la
11 years ago
Unless the tape is mastic tape it is worthless.
amen to that!
alan_s_thefirst
11 years ago
Lots of people here in British Columbia use mastic paint/paste, but lots use foil tape also. I didn't think there was any issue with durability, and it probably seals better than poorly applied mastic, I'd think.

I agree, the pex screwed to the duct is stupid and sloppy. HVAC people here do use PEX for in-floor heating etc, so why not radiators, I suppose.

What first caught MY eye, is the rim joists are uninsulated. Since they're so open and exposed, I'd be insulating them with ISOBOARD, the mylar faced stuff, or sprayfoam.
david_cary
11 years ago
I was just assuming insulation wasn't done yet and this was new construction.

I hadn't thought about the pex being for hot water heat. I just figured radiator was a misspeak - does anyone actually still do radiators anymore? Seems like it would be forced air or radiant in floor. If the ducts are for a/c and this is Canada, how much does it really matter if there is a leak at the screw hole. Sloppy yes but when the annual a/c bill is $50 a little leak isn't crushing.
mike_home
11 years ago
I find it amazing that there are four joists where the pex lines could be neatly and securely attached. Yet the installer choose to punch random holes into the brand new duct work.

You have to wonder what other corners were cut in this installation.
energy_rater_la
11 years ago
good catch allen.

second that the band/rim joist should be
air sealed and insulated.
spray foam or foam sheathing cut to
fit tightly & caulked to air seal.

according to code, paint on mastic
should be applied 'nickel thick'..
that's hard to do, but can be done.
lots of times I see just a thin thin coat
of mastic.
I can get 'dime thick' easily...doubling
that thickness takes more finesse. you
don't just get it right without trying.

the only tape I've found that doesn't fail
is hardcast brand #1402 mastic tape.
of course as with any tape, surfaces need
to be clean & dry for tape to adhere well.

best of luck.
JeannieMer
Original Author
11 years ago
Many thanks so far. I am pushing the builder for answers. Will let you know how this all turns out, your help is much appreciated.

Yes, this is an addition, and not yet insulated.....so that is up next. This previously exterior porch, will now be part of a family room.

And yes, we are keeping our existing radiators, adding a few more radiators in some rooms to keep costs down, and using underfloor Warmboard in most the the addition - family room, mudroom, and 3 bathrooms. The Warmboard was an extra $15K for the rest of the first floor, so we went with radiators. The pex is supplying the radiators.
ionized_gw
11 years ago
You guys obviously have it all wrong. That is the new "duct to PEX" heat exchanger.
JeannieMer
Original Author
11 years ago
Hi ionized. I'm not sure that we have a heat exchanger at all. Can you explain more?
ionized_gw
11 years ago
Sorry, Jennifer, that was a just a third-grade joke.
countryboymo
11 years ago
LOL Ionized. I am not so worried about the holes left behind after the screws pull out but the fact that after a few years and both lines are dangling having a water leak. In appearance it also just screams hack job.

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