Our humidity dictates that for spray foam projects to work they MUST provide BOTH insulation AND air sealing. Otherwise they remove sensible load while leaving significant latent load in place. That drops the home's total load and sensible heat ratio..."Foam Alone" (spray foam jobs that don't address HVAC system load and capacity) projects often leave clients with thinner wallets and discomfort.

I insist that any spray foam job with which we are associated be verified with blower door and smoke tests. We keep the foam crew on site, suited up, and spray rig ready while we smoke and blow the attic. There are almost inevitably significant eave air leaks, and the smoke rapidly illustrates the foam crew's incomplete work.

As soon as the foam job is relatively airtight, I worry not at all about duct leaks since the ducts are then within the home's thermal and pressure envelope, and thus duct leaks are largely contained within the home. Duct leaks then represent merely misdirected, rather than lost air...no problem.

Posted By engineer on 19 Jun 2012 11:08 PM 
Duct leaks then represent merely misdirected, rather than lost air...no problem.

Most of our ducts are in basements around here and leaks during cooling aren't helpful but regarding heating once upon a time we always said (regarding leaky ducts): everything you lose is still in the house.

Posted By joe.ami on 22 Jun 2012 10:21 AM

Posted By engineer on 19 Jun 2012 11:08 PM 
Duct leaks then represent merely misdirected, rather than lost air...no problem.

Most of our ducts are in basements around here and leaks during cooling aren't helpful but regarding heating once upon a time we always said (regarding leaky ducts): everything you lose is still in the house.

In an insulated air-tight basement that's sorta-true, but for the typical uninsulated semi-conditioned  basement with leaking foundation sills & band joist, open flues and not-so-tight doors and window with vent chases  and other interior paths leaking air all the way to the attic, the definition of "...in the house..." gets pretty squishy.

A tight house is not the solution to a leaky duct system any more than the converse- they're both worth treating, and the combination is good for double-digit reductions in heating & cooling energy use.

Pulling the ducts into the thermal and pressure envelope does two things:

1) Duct leaks matter less (or not at all, depending on the viscosity of the squishiness desribed above)

2) Ductwork's paltry R3-R8 insulation is augmented by the envelope's insulation such that ductwork conductive losses to outdoors are no longer a factor.

Posted By Dana1 on 22 Jun 2012 01:46 PM

 

In an insulated air-tight basement that's sorta-true, but for the typical uninsulated semi-conditioned  basement with leaking foundation sills & band joist, open flues and not-so-tight doors and window with vent chases  and other interior paths leaking air all the way to the attic, the definition of "...in the house..." gets pretty squishy.

A tight house is not the solution to a leaky duct system any more than the converse- they're both worth treating, and the combination is good for double-digit reductions in heating & cooling energy use.

So shall I say "it's still contributing to the house" instead. While all the conditions you describe may be true, the squishy leaky basement will penalize the system in duct loss, if not conditioned. Leaks can condition the basement.
Not suggesting any of these things are ideal, but they are real world (meaning the vast majority of people do not put time and thought into half of what we do here).

To be sure, HVAC losses to a semi-conditioned basement is a much smaller hit than to an unconditioned and vented attic.

"...the vast majority of people do not put time and thought into half of what we do here..."

Right again! I suppose I shouldn't be surprised when people in New England tell me that since their basement stays above 65F in the basement all winter they don't need to seal the basement an insulate the foundation, when the exact opposite is true.

Posted By Dana1 on 25 Jun 2012 05:37 PM

"...the vast majority of people do not put time and thought into half of what we do here..."

Right again! I suppose I shouldn't be surprised when people in New England tell me that since their basement stays above 65F in the basement all winter they don't need to seal the basement an insulate the foundation, when the exact opposite is true.

One of the most common responses I get when I suggest folks employ our energy analyst friend to blower door test the house is something to the effect of "I know where the leaks are".

Slowly the HVAC industry is starting to understand that attacking from the load side offers so many more benefits in comfort (et al) vs simply attacking the load.

It took me awhile, but I'm on board.

(this is one of the benefits I get from lurking here- education)

As long as my comments have little to do with OP,

WE WANT AN ASHP FORUM

now make sure you all alert the mods that I'm off topic

"I know where the leaks are"

Yup- that's a classic!  Even the air-sealing retrofit pros still get surprised.  I like engineer's pressurized house smoke machine testing approach. The air knows a lot better than the home owner or foam guy where the low-resistance air leakage paths really are.

Paraphrasing Samuel Clements:

It ain't so much the things you don't know that get you into trouble, as the things you know for certain that just ain't so.

I know where the leaks are in my house too (well, at least some of them, and some of those might even be important enough to fix, but I'm also convinced there are air leaks yet to be discovered.)

In theory, I'm totally on board with improving the envelope. Heck, I've only got 6 inches of smushed down cellulose in my 1977 attic - talk about low-hanging fruit. On the other hand, in practice it only cost me $320.00 to heat my 2100 sqft New Hampshire house last winter. And, wow, electric rates just fell another 15%. It would take a long time to payback that attic insulation.... I paid more than $320 for regular unleaded last month. Time to get a Prius? There's some strange economics introduced with geo and I can't quite wrap my brain around the big picture yet.

I never cease to be amzed by how hard it can be to substantially tighten a leaky house, even with the blower door and smoke machine.

I've had similar conversations with clients about competing improvements. I can double the SEER of an older existing system, which seems good, except that investment doubles the payback time of load side improvements. High efficiency creates a certain moral hazard - why conserve on the load side if the source side is so good?

I think it was Eric (WaterPirate) who related a story of a client who complained that geo didn't lower his bills as much as he had hoped - The guy opens the door wearing shorts in January - heating the house to 75+ and wondering why the bills are still a bit high.

People who buy Priuses (or in my case, a Diesel Jetta) may find themselves driving further more often. The abiliity to drive 800 miles for less than $75 causes more 800 mile trips to be made.

Source side improvement was a no-brainer in my case, even before attic insulation. A 100,000 BTU, 25 year old propane furnace with standing pilot. I'm guessing somewhere around 65% efficient at best. The ground floor was still freezing, so the previous owner installed a 40,000 BTU unvented propane "fireplace". My propane bill was $3,000 the first winter. The manual J calc? 27,000 BTU @ 0 degrees. Source side was killing me....

One of the off shoots of tighening up a home, is the improved comfort or eveness reported by folks prior to making any changes with the heat plant.
We simply can't ignore envelope as part of the "comfort strategy".

One of my happiest energy customers, while quite pleased with the 30-40% energy use reduction, is most pleased that he is finally comfortable in the home.

In my case, source side WAS the primary cause of discomfort in the home. I was the classic case study for GROSSLY oversized equipment. Once that nice steady mild-temperature heat replaced the cycling blast furnace, life was good. However, I'll grant you that I do definitely notice the paltry 6 inches of attic insulation during air conditioning season. I'm tall, and the ceilings are short. But central AC vs no AC kinda makes up for that shortcoming.

I find the use of the term "source side" confusing.
If this refers to the heat plant, then you should not have been undersized as you mentioned a large furnace and a 30K load.
Infiltration caused by the furnace sucking combyustion air may have made it inadequate if your home is loose.
Tightening up may have improved your comfort and taken much off your bill pre geo.
You can choose to ignore one side of the equation.
In my business it's bad customer service.
Orange or Blue store blown in insulation still might improve your summer comfort for a modest enough price to make it worthwile.

Sorry - I thought I saw you guys using "source side" for heating plant. I can see why you're scratching your head on why my grossly oversized heating unit couldn't keep my house comfortable and how the geo unit is saving me not half on my energy bill, but almost 90% with no improvements to envelope and with far greater comfort.

WAIT! I actually am ON TOPIC! The duct system was just as poorly designed as the furnace was sized. The ground floor is a partly-burried basement. Total load is only about 7,000 BTU at 0 degrees, but it was Impossible to keep warm with the old systems installed. Dumping tons of super-hot air at ceiling level, plus the unvented, uncirculated propane fireplace created the MOTHER of all stack effects. That hot air would rush up the open staircase, into the false ceiling with uninsulated band joists and straight up the chimney of the leaky fireplace and every other hole it could find a way out. My old system was amazingly efficient at pumping cold air into the house. Like I said, the poster child of what can happen with grossly oversized equipment.

Posted By joe.ami on 27 Jun 2012 09:35 AM
One of the off shoots of tighening up a home, is the improved comfort or eveness reported by folks prior to making any changes with the heat plant.
We simply can't ignore envelope as part of the "comfort strategy".

While I agree completely, I'd take that (perhaps predictably) a bit further to say, the the envelope is the PRIMARY component of the comfort strategy. 

Air tightness is essential for good humidity control (winter or summer), and at least current code min on the windows makes a real comfort difference at the temperature extremes, whether the HVAC is keeping up with temperature or not.

Hot air furnaces that are 3-4x oversized for the actual load are pretty common in my area.  While the oversizing of very low-mass burners like hot-air furnaces has negligble impact on efficiency, gross oversizing like that takes a toll on comfort, with much higher air volume/speed and short burns with overshoots, etc.  While only a few propane ducted-air furnaces put out less than 35KBTU/hr, several smaller 2-stage condensing units do (many with sub-30K input at low fire) and with properly sized & sealed ducts would make a pretty big improvement on both comfort and efficiency. But it would never come close to touching geo on operating costs. 

Blake, so the duct work was much of the problem, vs heat plant?

Dana we come at projects from different angles with the same goal. I get the symbiosis of load and heat plant, at the end of the day I only sell heat plants. I do not let that keep me from recommending things I don't sell, but I'm not likely to see load side as primary

I'd say ductwork was a huge part of the problem. I started with a clean slate when designing duct work for geo. Twice the duct for half the capacity and zoned top and bottom. Every room has a return - (no dampers on returns). I don't know how hot the air is supposed to be with a fossil fuel furnace, mine was roasting, which probably points to inadequate flow - despite (or indicative of) the roar in the ductwork. I'm fingering misdirected and very high temperature heat sources (unvented fireplace included) as the root of the stacking problem. Is an oversized heat-plant(s) or poor duct work to blame? Probably a combination. All I know is that with a lower temperature heat source (sorry, heat plant) and better ducting, there is significantly less heat loss even without doing anything to the envelope.

Regardless, the 25 year old dinosaur in the basement with the 8 inch chimney needed to be replaced. No one can convince me that any amount of envelope improvement would provide a better ROI than replacing that beast.

Not trying to convince you of anything Blake. In fact I've learned along the way here that there are less absolutes than I once believed. I handle every design as a stand alone case.
In one case I discussed today I recommended insulation/energy analysis and electric baseboard (none of which I sell) as payback horizon for extra money spent on different heat plants was waaaay out there.
"heat source" I get vs source side as there is the source of the loss and the source of conditioning.
Never trying to bust your chops, just wanted to know we are on the same page.
j