Air conditioning an attic requires some evaluation of the space before purchasing a unit. Homes that have an accessible attic space offer a tempting area for square footage expansion; this top floor can easily become an office space or extra bedroom for a growing family. One major challenge for the attic area is air conditioning the space. Heat naturally rises and the attic is a prime location to accumulate this heat from the main portion of the house. However, you have a number of different air-conditioning options to create a comfortable area. Window or Wall Units A room conditioner offers you an air-conditioned attic by installing it in a window or wall opening. When the attic has window access, a low-cost window unit is a practical choice; it can easily be installed within the window opening with limited hardware needs for securing the assembly. You can simply plug the appliance into a wall outlet and cool the area quickly. A more expensive room conditioner choice is the wall-mounted versions.

These units require a large hole to be cut out of the attic wall. Depending on the shape of the attic, this attachment choice may not be possible and can be expensive to implement when the wall space is actually available. However, a wall-mounted unit can free the window space to allow light into the area, if equipped. Ductless Mini-Split Systems A ductless mini-split system acts much like a central air-conditioner unit but without the need for ductwork; half of the system is in the attic while the remaining portion is outside near the side of the home. Air conditioning the attic with this system is a more permanent solution than a room conditioner hanging on the side of the home. A conduit housing power cables, condensate drains and refrigerant tubing must be run between the indoor and outdoor units with no more than 50 feet between the two assemblies. The installation requires a 3-inch access hole for the conduit running out of the attic. However, the 50-foot limitation can only work with homes that are one or two stories tall, depending on the structure's construction.

Portable Air Conditioners A less-invasive way of air conditioning the attic is purchasing a portable unit. These air conditioners are more of a temporary solution; they require floor space and a way to exhaust the hot air, such as through an opening or window. When the attic space is used sporadically, consider a portable unit as an air-conditioning choice. It does not require installation hardware or extensive alterations to the attic space and plugs into an existing wall outlet. Insulation Considerations No air-conditioning device can function correctly without the proper insulation in the attic. Many attics do not have any insulation; they simply have a roof and rafters. A simple solution is to roll out some fiberglass blanket insulation between the rafters and closing it off with plywood. Some homeowners would like to go further in their insulating process and install spray insulation. Although more effective at insulating an area, it can be messy and extremely expensive. Regardless of the insulating choice, the air conditioner now has a barrier to the outside elements to retain the cooled air.

References Good Housekeeping: Buying an Air ConditionerU.S. Department of Energy: Ductless, Mini-Split Air ConditionersU.S. Department of Energy: Room Air ConditionersU.S. Department of Energy: Attic Insulation Photo Credits Jupiterimages/Creatas/Getty Images Suggest a Correctionductless ac ceiling units Move over powered attic ventilator. frigidaire energy star ac unitThere's a new boss in town. jual ac portable murah di bekasiFor decades, concerned homeowners have looked for ways to keep their attics cool: gable vents, ridge vents, turtlebacks and whirlybirds. Then they moved from passive to active and latched onto the powered attic ventilator. Now we don't have to settle for a technology that pulls conditioned air up from the house.

Keeping your attic cool is a perfect application for the mini-split heat pump. The Ginzu Corporation, which makes the sharpest air conditioners in the world, has just introduced a new line of powered attic mini-split heat pumps, affectionately referred to as PAMS. The biggest advantages of using ductless PAMS are: Unlike powered attic ventilators (PAVs), PAMS won't pull conditioned air from your house. And they don't need to because they make conditioned air right in your attic, where it's needed! Ductless PAMS have no ducts...and thus no duct losses. Ducts in attics are a really bad idea because they waste so much energy. In winter, they can make ice-dam-preventing strip heaters unnecessary. Automatically set to heat in winter as well as cool in summer, PAMS will keep the roof so warm that snow will melt immediately and never get a chance to form ice dams. PAMS work great with Celluloaf insulation, too! To give you a feel for how sharp they are, Ginzu is offering you a 7 piece set of ductless PAMS at a special introductory price.

Call now, though, and you can get a 10 piece set for the price of 7 and have your attic pre-chilled before summer even starts.This special offer is good today only. Note: Happy April Fool's Day! Please don't actually try using mini-splits to cool your attic in summer or prevent ice dams. US Green Building Council to Require All-Glass LEED Homes RESNET Enters into Strategic Alliance with Int'l Jugglers Association The #1 Reason Power Attic Ventilators Don't Help2012 was a hot one. We’ve had at least 31 days over 90F, something which hasn’t happened since 1988, and July 2012 was the second warmest July on record in the Twin Cities. This is a departure from the norm; for example the average number of 90F days is 13 – we almost tripled it this year.  The 1930’s homes in our neighborhood weren’t built with AC, and retrofitting ductwork is tough.  And although I obsess over our energy use like some people obsess over Kim Kardashian, we do have to be able to function on those sweltering days.  

Last year we struggled through the hot week with a single 8,000 BTU window unit upstairs, which was cumbersome, noisy, ineffective, and inefficient. This year we decided to give in and install something more efficient, permanent, attractive, and convenient – a Fujitsu ductless mini-split AC (our model is here). These units come in various configurations, but simple ones like ours have an outdoor compressor/condenser similar to central AC and a single indoor air handler that hangs on the wall.  Refrigerant, power, and control lines run back to the outdoor unit.  Because it’s a matched set, and because there are no ducts to blow through a hot attic and leak air, they can be very efficient – ours is 25 SEER, 13.8 EER for cooling.  For comparison, Energy Star standards for central AC require >=14 SEER/ >=11 EER. We weren’t going for perfect comfort, just something to keep it tolerable, and keep the upstairs cooler at night for sleeping.  One consideration with these units is that they are a single point of conditioning, and distribution can be an issue*. 

We installed only one unit at the top of the stairs, figuring some cold air could fall and hot air could rise.  If we’d been going for more consistent whole-house comfort, at least one more head would have made sense, and we may still do that in the future. In the end, we selected a single 12,000BTU (1 ton) unit after doing a whole-house heat gain analysis to determine the necessary cooling capacity.  I contacted the fine folks at The Neighborhood Energy Connection in Saint Paul to do the analysis. Overall, it’s been pretty good.  We put it in just before a perfect storm of hot:  103F days, both sides of the family visiting, and a birthday requiring use of the oven to bake a cake.  That was a struggle, but it kept things reasonable – around 80F downstairs – and much drier, which makes a huge difference.  Distribution was a bit of an issue; it’s hard to cool a hot kitchen with a unit on the 2nd floor. Here might be a more representative day: Sept 11 2012 had a high of 93F. 

We closed the house and set the unit to 74F at about 11:00AM, and turned it back off around 7pm.  The bigger spikes are likely the espresso machine.  Stuff later in the evening is cooking & running the dishwasher. The graph shows indoor & outdoor temperatures, solar PV power production, and household power use.  Outdoor temp peaked at 93F at 4pm, and indoor temps on the first floor peaked at about 76.5F around 1pm.  On the energy side, we used 13kWh and produced about 13.5kWh.  If we’d anticipated a string of hot days, we would have just left it on 24/7 to keep things cool and dried out. In July 2011, with the window unit struggling to keep up, we used 33kWh-38kWh per day for the hot days.  In July 2012, with the mini-split running 24/7 on the hottest days, we used between 19kWh and 28kWh per day – quite an improvement. The unit can also work in reverse, as an air-source heat pump, with an HSPF of 12.0, meaning for every BTU watt-hour it consumes, it moves 12 BTUs of heat into the house. 

Converted to Coefficient of Performance, this indicates that it transfers about 3.5 units of energy into the house for every unit of energy it consumes – or 3.5x more efficient than a resistance space heater.  It maintains rated heating capacity down to 20F outside, and continues to function even in -5F weather. I haven’t yet decided if we’ll use it much for heating, but it might make sense in the “shoulder seasons” when our 83 AFUE boiler would be operating infrequently and at lower efficiency.  Because these electric units can heat and cool so efficiently, they are often used in the design of well-insulated net-zero or near-net-zero homes with PV installed. Overall I’m pleased with this thing.  It’s quiet, efficient, attractive, and made the hottest weeks quite tolerable.  It helps that we’ve done air-sealing and insulation of our home, so the single unit is better able to meet our cooling load.  I may experiment with sun control screens on the south windows next year to cut down on solar heat gain.