Home Energy Improvents with best ROI
I recently moved into a new construction home in Phoenix, AZ and assumed it would be energy efficient, but after only a short time in the home I am finding it is not so. It is a smaller 1600sq ft single level home, concrete tile roof, it has R19 wall and R30 ceiling insulation, lowE windows, CFL’s, 15seer ac unit to name a few.
What are some cost effective energy improvements that will make our home more energy efficient in this hot climate? We have added shade screens, and I am considering a radiant barrier in the attic as well as garage door, but other than that I can’t think of many options I have.
Any input would be appreciated.
Adam
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Replies
Air sealing, particularly at the attic-floor plane is usually very cost effective, and a necessary preliminary to attic insulation.
If you have ducts in the attic above the insulation (a bad idea, in any climate, but common in AZ), air-sealing and insulating the ducts and air handler is cost effective (it's imperative- in fact!) In CA duct tightness is required to be under a specified and tested maximum leakage, and with good reason: Duct leakage is a major driver of outdoor air infiltration, and potentially pulls fiberglass-contaminated attic air into the house. Before that became code, in most homes 15-25% of the AC air was going somewhere other than intended, and 40%+ wasn't uncommon(!). Even the most efficient AC unit & houses were getting cut off at the efficiency knees with leakage like that. Unless you've had your system tested with a duct blaster, you don't really know where it is relative to what it could be. Fixing the obvious like going around to each register and caulking the duct boot to the ceiling or wall gypsum is both cheap, and necessary, as is mastic-sealing every seam & joint you can get to on the ducts themselves, and sealing the seams of the air handler with FSK tape (aluminum duct tape.)
If the attic insulation is low-density blown fiberglass or R30 batts, blowing 6" of cellulose over the top will be cost effective. Low density fiberglass is translucent to infra-red radiation, and the temperature an inch or two into the top side is usually hotter than the attic air on a sunny afternoon (meaning you're insulating against a higher temperature with ~2" less insulation!). At low densities fiberglass is also not very air-retardent. Cellulose is IR-opaque, and an order of magnitude more air retardent, and even a 3" overblow of cellulose "restores" performance to the existing fiberglass while adding another R10. A 6" overblow would give you an ~R50 nominal attic R, but would also add a modest amount of thermal mass (not that you really need more, given the concrete tile roof.)
With even R19 in the attic and modestly insulated ducts radiant barrier wouldn't be buying you much in efficiency- not nearly as much as applying the same money to more cellulose (assuming you're under R-60). A mop-on high solar reflectance "cool roof" coating would usually do a bit better in both absolute performance and in performance-per-dollar. To see just how low the marginal improvement is for radiant barrier, once you have code-min R and insulated ducts, see the table on P5 of this document:
http://web.ornl.gov/sci/ees/etsd/btric/RadiantBarrier/RBFactSheet2010.pdf
A thermal-imaging scan might tell you how well the R19 in the walls is really performing, or if it's even there! Gaps & compressions are common, and missing insulation (particularly on a side that gets direct sun) can be a significant fraction of summertime heat gain (and wintertime loss.) Spot retrofitting insulation in walls is possible, but from a bang/buck point of view it's usually well behind exterior window shades, air sealing, and attic insulation.
Adam,
Dana has given you good advice.
If you are not sure what to do, the usual first step is to hire a home-performance contractor to do an energy audit. Choose a contractor or home rater who is certified by RESNET or BPI. At the end of the energy audit, you will receive a prioritized list of energy-retrofit projects that is customized for your house.
More information here:
Energy Upgrades for Beginners
Hot-Climate Design
Keeping Ducts Indoors