Sorry about the brevity, but I am under the gun here.

I am in process of building a new house in Joplin, Missouri.  It is ICF, with open cell spray foam in the roof rafters.  I was originally going for energy star, but having difficulties with my General Contractor's HVAC subcontractor (and the GC).  Both insist that I do not need to seal my air ducts because it is within the thermal envelope.  Which they are.  My contention is that if there are leaks, the desired heating/cooling may not be getting to the rooms intended.

I decided to forgo getting energy star (for a variety of reasons), but I would still like to hit its important tenets.  How important is sealing the supply/return air lines?  The subcontractor is refusing to mastic/tape the joints eventhough I'd pay more for it.  They both say its throwing good money after bad.

I've looked inside the ductwork, and I honestly cannot see how air can get passed the joints and the insulation within the ductwork.  I can see leak paths at the registers, but they are very small holes.  Youtube shows mastic over these same size holes.

Am I overreacting, or is this something I should rant and rave about until it gets fixed? 

Thanks in advance for any advice,

Matt

Hi Matt IMHO your the boss, you want it done that way , they should do it that way, Taping joints doesn't take long. I did it in my home particularly where the insulated flexible duct met the galvanized solid runs. Consider someone closing off an air diffuser and the increase back pressure could eventually work the connection loose or at least cause more leakage than desirable My two cents

I remember reading that about 20% of all duct work eventually leaks. With that being said, your duct work is WITHIN the thermal envelope of the home, so you've won most of the battle right there. Putting your duct within the thermal envelope of the home saves you about 30%-40% in energy costs over not within the envelope.

Not taping the duct work is PLAIN LAZY and how much more $$ are we talking about? $100 - $200??? Your GC is an idiot for talking to you that way and I would just DIY. Go to Home Depot and buy the stuff and DIY if he doesn't want to do it.

I'd fire your GC for 2 reasons,

One for being an idiot, it's a cheap solution to seal the ducts, you know about it, it's the proper way to do it

Two for hiring and HVAC contractor who is an idiot


If your current basement is unfinished, turn of the furnace fan, and use a lighter or a cigarette (if you smoke) hold it by the joints on all your duct work. Case closed.

Although it is leaking within conditioned space it is leaking in the an area not where intended, the termination point (register) is where it needs to go.

Thanks for the replies! It is such a small cost, that I cannot believe they are balking. Since only the garage will be finished at this time, I went to HD and got some mastic and tape. Will get that taken care of, and once I move in, will test the duct work to gauge the magnitude of the problem. For now, just the seams, and the registers in the garage area (about 6-7 areas I think)

I am a bit limited on ICF contractors in my area (though the ICF portion is up at this point). Lot of GC's said they could do it, but still pushed SIPs and advanced construction with CC spray foam. None had installer crews lined up. And I talked to about 6 GCs.

My GC and sub doesn't recommend ERV's either. HVAC guy said they work great for a year or two, then they fail and homeowner is none the wiser. Obviously I will have neither install one. I will have to find a good one and put it in after the fact. Luckily my attic will be conditioned space =)

HVAC guy said they work great for a year or two, then they fail and homeowner is none the wiser.

They do require some regular homeowner maintenance, and I know one brand had some troubles with their motors, but am wondering how else they might "fail".

If you do have a tight home, seems like you are going to notice when air doesn't get moved anymore.....

Posted By matrim72 on 20 May 2012 09:52 AM


My GC and sub doesn't recommend ERV's either. HVAC guy said they work great for a year or two, then they fail and homeowner is none the wiser. Obviously I will have neither install one. I will have to find a good one and put it in after the fact. Luckily my attic will be conditioned space =)

With an ICF home, ERV's are mandatory not optional. Unless you are going to keep the windows open all year round. Nothing like living in a tight home and breathing the same stale air over saturated with carbon dioxide and whatever off-gassing you have from paint, carpet, glues, etc.

For your GC to state that ERV's fail in a year or two is like saying A/C's fail, so why install one? Anything can "fail" but if you research and find a reliable unit and do proper maintenance on it, it will be reliable and run a long time.

I'm sorry but your GC sounds like a complete fool. First with the HVAC duct thing and now with the ERV.

Actually their idea was just to drill through the concrete and put a manual operated flapper on the supply lines. That way it partially pulls from outside. Only downside is the lack of heat transfer between outgoing and incoming air.

Posted By matrim72 on 20 May 2012 07:09 PM
Actually their idea was just to drill through the concrete and put a manual operated flapper on the supply lines. That way it partially pulls from outside. Only downside is the lack of heat transfer between outgoing and incoming air.

You would be pulling in unconditioned air (waste of energy) and you still have the problem of the stale air in the return line going where? It would just recirculate the stale air back into the home.

An ERV creates an equilibrium of bringing in fresh air and expelling the same amount of stale air back to the outside. Plus it filters the air and conditions the incoming air.

Remember, all commercial buildings utilize MECHANICAL VENTILATION. It is not a new concept and since this GC is clearly out of his league in knowledge of this area or he has never built a commercial structure, he would know that ERVs and mechanical ventilation is reliable and used by millions.

Posted By matrim72 on 20 May 2012 09:52 AM
Thanks for the replies! It is such a small cost, that I cannot believe they are balking. Since only the garage will be finished at this time, I went to HD and got some mastic and tape. Will get that taken care of, and once I move in, will test the duct work to gauge the magnitude of the problem. For now, just the seams, and the registers in the garage area (about 6-7 areas I think)

I am a bit limited on ICF contractors in my area (though the ICF portion is up at this point). Lot of GC's said they could do it, but still pushed SIPs and advanced construction with CC spray foam. None had installer crews lined up. And I talked to about 6 GCs.

My GC and sub doesn't recommend ERV's either. HVAC guy said they work great for a year or two, then they fail and homeowner is none the wiser. Obviously I will have neither install one. I will have to find a good one and put it in after the fact. Luckily my attic will be conditioned space =)

Installing ducts without sealing them is just malpractice.  I can see not TESTING them (unless required by code, which IS the case in CA, IIRC), but if they're arguing that they needn't even bother sealing them, they're total hacks IMHO.  The odds don't look good on their having done anything like a Manual-J heating & cooling load calculation or a Manual-D duct design either, given their attitude regarding duct sealing. 

Hopefully they at least went with insulated supply ducts?

Any home that has inherently tight walls, and is being insulated with spray foam is going to be tight enough to require mechanical ventilation. There is no indication that theses system fail at high rates after "a year or two", quite the contrary- you'll get more than a decade out of any of them unless you ice-up the core or something.  (ERV cores are more sensitive to damage than HRV cores, but still recommended anyplace with summertime dew points that average over 60F, which they do in most of the US midwest) They're not maintenance-free- you have to keep the filters clean to keep the ventilation rates up.

They are insulated ducts. Upon looking at them, I cannot see how they could leak. I guess my paranoia got the better of them and they caulked the duct joints. I still plan on sneaking in and applying mastic to the registers and returns. All the crimps look well designed, so it is hard to see air leakage through the insulation and through the joint edges.

I plan on testing the ductwork in the basement (only have to "treat" the garage ductwork since it will be insulated and covered with drywall and therefore be inaccessible). I watched a video on you-tube that showed if a return held toilet paper against it, or a supply pushed a string away, there is leakage. I plan on running this test on all exposed areas before I seal the basement up.

I will start researching ERVs and either install it myself, or find someone that believes that they are needed and recommends them. I probably can get away for awhile. I have roughly 22500 ft3 of air in my house and I live alone, and am at work for a good portion every day. I bet normal opening and closing doors should do, but I will be monitoring the IAQ.

Posted By matrim72 on 21 May 2012 09:06 PM
I live alone, and am at work for a good portion every day. I bet normal opening and closing doors should do, but I will be monitoring the IAQ.

I'll venture the opinion that is one reason why you will need ventilation. Being gone most of the day means no one will be opening and closing so that will not provide any significant amount of air change.

I have the Ultimate Air 200DX ERV. So far it has been great. The main reason I got it when I built this house in 2008 is it was the only one at the time, and maybe still, that offers an economizer feature. The exchange wheel turns off and it exchanges air with no heat recovery. This helps in the summer by bringing in cool air at night while exhausting the warm house air. I have it wired to a separate a/c thermostat so it's automatic. I ordered the timer with the ERV. I have it set to run at low speed for about 20 minutes every 2 hours. I have never detected any odors in the house or other air problems.

Sounds like the guys you're working with have never heard the new mantra in building, "Build it tight and ventilate it right!"

Hmmmm. I figured the danger of no air exchange was never getting rid of the CO2, not some other reason. That is why I figured I could get away with not ventilating right away. I mean, if I were not at home generating CO2 then I'd hardly have to exchange it. I guess I have some more research to do. *sigh*

Matt

Moisture and volatile organics are generally bigger indoor air quality issues than CO2 it a tight house, (especially in a new home.) High humidity increases the mold spore counts, and all sorts of building materials outgas stuff for the first year or so, and the moisture content of fresh concrete & new wood is also pretty high. In air-tight houses human-sourced humidity doesn't automatically leave either (but outdoor humidity from high-dew-point summer air doesn't find it's way in by accident either.)

Air tight is a good thing for comfort and energy use, but it does require a ventilation plan, and ERV/HRV allows higher ventilation rates without impacting energy use. Ideally homes will not go below 30% relative humidity @ 68F in winter or above 50%RH @ 78F in summer. In a higher-R high-mass house the air conditioning won't always run long enough to purge the moisture from interior sources like cooking, breathing, and bathing. For most of the year you can simply up the ventilation rate to reduce humidity into the healthy range. But the dew point of air 50%RH/78F air is about 58F, and between half-past May and mid-September the average outdoor air dew points are higher than that in Joplin. (see: http://weatherspark.com/#!dashboard;a=USA/MO/Joplin - pull up the graphs for dew points as well as temperature.) When the air conditioner is running it'll likely take care of it, but only if you throttle back on the ventilation rates during those weeks, but you may still need to run some mechanical dehumidifier (even if it's just a room dehumidifier placed in a cooler spot in the house like the basement).

House plants can reduce CO2 and some other indoor air pollutants for the periods where you have to back off on ventilation, but if you use an ERV (rather than HRV), which does a humidity exchange as well as a sensible-heat exchange between the incoming and exhaust air streams, you can still run reasonable ventilation rates without adding a huge amount to the dehumidification load. It takes about twice as much AC-compressor energy to reduce the dew point of the air 10F than it takes to reduce the temperature of the air 10F. So when it's 88F outside and the dew point is 68F, and you're holding the line at 50% RH, fully 2/3 of the cooling load for ventilation air is the humidity. With an HRV the temperature exchange of that incoming stream may be 75% or even 95%, but that's less than a 1/3 reduction in the cooling load. With an ERV it may only exchange half the humidity and 75-90% of the temperature, but that's now well over half the cooling load avoided. ERV is definitely preferable to HRV in your climate.

Posted By Dana1 on 22 May 2012 10:55 AM
House plants can reduce CO2 and some other indoor air pollutants for the periods where you have to back off on ventilation, but if you use an ERV (rather than HRV), which does a humidity exchange as well as a sensible-heat exchange between the incoming and exhaust air streams, you can still run reasonable ventilation rates without adding a huge amount to the dehumidification load. It takes about twice as much AC-compressor energy to reduce the dew point of the air 10F than it takes to reduce the temperature of the air 10F. So when it's 88F outside and the dew point is 68F, and you're holding the line at 50% RH, fully 2/3 of the cooling load for ventilation air is the humidity. With an HRV the temperature exchange of that incoming stream may be 75% or even 95%, but that's less than a 1/3 reduction in the cooling load. With an ERV it may only exchange half the humidity and 75-90% of the temperature, but that's now well over half the cooling load avoided. ERV is definitely preferable to HRV in your climate.

In a high-desert dry climate like Northern Arizona, would you recommend an ERV or HRV?

Posted By Lbear on 23 May 2012 12:20 AM
In a high-desert dry climate like Northern Arizona, would you recommend an ERV or HRV?

SW Idaho is probably not as dry as AZ, but close. I find the ERV works quite alright. My HVAC installer guys were concerned because they felt the humidity in the house would climb to unacceptable levels during the winter. However, my house humidity has been about 30% in the winter, and maybe up to 40%+ in the summer. I can definitely tell the house is more humid than the outdoors when I come in, but the sensation of the difference disappears in about a minute. Basically, in this dry climate the house humidity is staying within the comfort range quite nicely. Contrary to common opinion, I think the ERV is serving me better than an HRV would have. Right now it's 74° in the house, 57° outside, the RH is 37% inside and 27% outside, and the AC has not run all day.

My experience would say get whichever machine does what you want the best, whether it be ERV or HRV.

Plug your location into Weatherspark, go over to the "graphs" tab and bring check "dew point", then scale the graphs to show an entire year's data.  Use the cursor to eyeball the average summertime dew point. If the average is north of 60F the incentive to go with ERV is pretty strong, but if is under 55F, an HRV would be fine, year round. 

To keep from over-drying in winter, run it on dehumidisat set to 30-35%RH during the winter months, but in the warmer weather you'd need a different approach to guarantee minimum ventilation rates.  Most of AZ has summertime dew point averages in the 40s, even though it may peak well north of 60F, the 1-3 muggy days/year aren't going to be enough to tip the balance toward ERV. 

FWIW, northern AZ locations tend to be drier on average than southern AZ, probably due to proximity to the Gulf of California in the southern region.  (I've experienced torrential 100F rainstorms in Tucson- complete with bar of soap & shampoo in hand, but that doesn't happen in Flagstaff or Kingman.)

Here in Michigan you have no choice, if in an unconditioned space all duct seams must be sealed (tape, mastic, etc) per mechanical code and my inspector wanted everything inside sealed as well.  I agree with everyone else, sounds like your contractors are lazy.

Posted By mike597 on 15 Jun 2012 02:44 PM
Here in Michigan you have no choice, if in an unconditioned space all duct seams must be sealed (tape, mastic, etc) per mechanical code and my inspector wanted everything inside sealed as well.  I agree with everyone else, sounds like your contractors are lazy.

But in this instance the contractor is arguing that by virtue of being fully within the pressure & thermal boundary of the house (an unvented attic insulated at the roof deck) the attic is in fact a conditioned space (which it is).  

That's still no excuse though.  IRC 2012 chapter 16 specifies sealed ducts independent of whether the duct is inside of conditioned space or not, and there's good data to back up it's cost-effectiveness.