[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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