[Greenbuilding] New HVAC unit

Bob Klahn Home-NRG at dnaco.net
Wed Jun 1 21:10:14 CDT 2011


Bobbi,
I agree that blowing cellulose into the walls and ceiling are your best 
initial reinsulation options. With caveats.

1) Blowing the attic can be an easy DIY - assuming that you have good 
access and that it's all open, flat attic - no kneewalls or "slopes" 
(the top floor ceiling that follows the rafter line.  If it's a walk-up 
attic, so much the better.  Is any of it floored for storage?

2) Prep work to seal _all_ penetrations of the ceiling plane.  This will 
require digging through/displacing the existing insulation to find them 
and to get sealing access.  It's labor-intensive, and in that heat best 
done in the winter or on rainy days.  However, it is *essential* to 
avoid losing much of the insulation value you (will have) worked hard 
for.  (I know of no insulation contractor in this market willing to even 
consider doing it, even though - or perhaps because - it could easily 
double the cost of the job.)  After that, adding insulation is easy.

3) I agree that you would be wise to blow the exterior wall cavities 
yourself - unless you can find an insulation contractor - and, more 
critically, installer who is familiar with dense-pack blowing techniques 
and will include in the contract assurance that all cavities were 
located and filled- and that all were filled to dense-pack densities.  
Offering to verify with an infrared scan, or agreeing to an independent 
one you contract yourself, is a strong plus.  If they don't offer one, 
you should find someone who will do one independently.
If you decide on - or are forced into - doing it yourself, email me; 
I'll be happy to send instructions or talk you through it.

4) Look for an Energy Rater in your area, with either RESNET or BPI 
certification, to run a blower door test on the house to locate the air 
leaks; a house that age is very likely to have lots and controlling them 
is critical for controlling comfort, costs, and the mold potential.  The 
Rater could also do a full analysis to determine what the "design load" 
(how big an A/C you really need) is - and what it will be after you 
re-insulate and air tighten.  Ask your HVAC dealer if he ran "ACCA 
Manuals J, D, and S on the house to determine the size units (condenser 
and evaporator) you 'need'; the duct sizing and reductions for the 
proper delivery flows and what the design flows are for each room.  In 
my experience, most don't; it's too time-consuming so they rely on 
"rules of thumb".  The only thing the ROT's will guarantee is that you 
will not get the most efficient installation.

Too large an A/C unit will keep you cool, but will not run long enough 
each time it cycles to adequately dehumidify.  When allergies and mold 
are concerns, this is critical.  Mold, and a number of other allergen 
producers just love the elevated humidity...

I don't know what your cost and completion limitations are, but I always 
advise clients to plan these upgrades in stages - but never to do 
something that will have to be undone, or redone, to implement the next 
stage.  Blowing the walls /and/ adding a layer of wall/insulation can 
make an expensive job astronomical.  The sheath wall can be added as a 
later stage.

There, I've slid into loggaria again.  Sorry,all.  But simple advice can 
so easily get twisted.  Besides, I avoided cleaning up the kitchen for a 
bit.  For that, I thank you.



On 6/1/2011 5:07 PM, Bobbi Chukran wrote:
> I'll bet he didn't live in Central TX, though.  :-)
>
> It was 90 there yesterday, and is supposed to be 100 for most of this 
> week.  Even though that house was built to be cooler *in the time it 
> was built* the climate has changed.
>
> There are also health issues to address, such as the high mold counts 
> here and allergies.
>
> bobbi c.
>
> On Jun 1, 2011, at 2:25 PM, Reuben Deumling wrote:
>
>> I once had a professor who asserted that the presence of a compressor 
>> AC in a house was a sign of poor design. In other words there were 
>> (in principle) ways around using AC in all climates>>>
>
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