ENERGY STAR Homes

Frequently Asked Questions by Homebuilders

If you have a question about ENERGY STAR homes that you cannot find an answer to online, email us and one of our technical support specialist will get back to you.

What are the technical specifications for an ENERGY STAR home?
Will participation in the ENERGY STAR Homes program disrupt construction schedules in any way?
How is air sealing specified and quantified?
Can an especially airtight house lead to what is known as Sick Building Syndrome?
What is the point of air sealing if it must be done in conjunction with bringing fresh air into the house?
What are the relative advantages and disadvantages of the different types of rigid foam boards?
Can insulation be used to air seal houses?
What guidelines should I follow when installing fiberglass batts?
What are ENERGY STAR windows?
From the standpoint of energy efficiency, what are the best windows currently available?
What is the best window strategy to maximize passive solar gain?
For my current project, I want to use a large wooden entry door that I salvaged from an older home. Will there be any penalty for this?
What are some important considerations when designing an HVAC system for an ENERGY STAR Home?
Is one type of distribution system more energy-efficient than another?
What are the relative advantages and disadvantages of a furnace vs. a hydro-air system?
What are the consequences of "oversizing" a heating and/or air conditioning system?

What are the technical specifications for an ENERGY STAR home?

There are very few prescriptive requirements for building an ENERGY STAR home. The basic requirement is that you achieve a minimum level of energy efficiency (at least 85 points on the Home Energy Rating System (HERS) scale. Different builders use different specifications to achieve this level of energy efficiency. Typical specifications for an ENERGY STAR home may include one or more of the following: enhanced insulation levels, high performance windows, air sealing and ventilation, and/or high efficiency heating and cooling equipment.

Will participation in the ENERGY STAR Homes program disrupt construction schedules in any way?

Usually there is no disruption. Only two site inspections will be performed during the course of construction. The main purpose of these inspections is simply to confirm that the specifications for the house are consistent with a set of previously established ENERGY STAR Homes Project Specifications. It may be advantageous, however, to budget extra time for the "rough" construction of the house–from framing to drywall. This would create valuable, extra time for careful air sealing and for a quality insulation installation.

How is air sealing specified and quantified?

Air sealing is specified as a Maximum Allowable Infiltration Rate that can be expressed as an equivalent leakage area (ELA), Air Changes per Hour (AC/H) or as a fan flow at 50 pascals (CFM50). The infiltration rate is quantified at the time of the final inspection by performing a blower door test. When builders first participate in the ENERGY STAR Homes program, conservative assumptions are made about how airtight their building(s) will be. In these cases, the Maximum Allowable Infiltration Rate can usually be achieved with a minimum effort.

Can an especially airtight house lead to what is known as Sick Building Syndrome?

The answer is "yes"! That is why we make mechanical ventilation one of the few prescriptive requirements for all ENERGY STAR homes. As a builder, your goal should be to build your houses as airtight as possible and then to complement this airtight construction with a mechanical ventilation system that delivers a sufficient quantity of fresh air to the house. This will help promote good indoor air quality. For more information about mechanical ventilation, please see the following Q&A as well as the Mechanical Systems section.

What is the point of air sealing if it must be done in conjunction with bringing fresh air into the house?

Many studies have shown that houses that are air sealed and mechanically ventilated have significantly lower operational costs than conventionally built houses. The approach used in conventionally built houses is to leave ventilation up to chance, hoping that random leaks will consistently provide just the right amount of fresh air to the house. We know that this does not happen. There are times when leakage will occur at extremely high rates due to driving forces such as wind and temperature differences. Conversely, there are times when natural infiltration rates will be greatly diminished. The better way to take control of energy costs and indoor air quality is to air seal and ventilate.

What are the relative advantages and disadvantages of the different types of rigid foam boards?

There are three different types of rigid foams: Expanded Polystyrene (EPS), Extruded Polystyrene (XPS) and Isocyanurate (ISO). EPS is sometimes referred to as "bead" board. It has the lowest R-value per inch (4) of the three rigid foam boards but it has the highest permeability. It is not as durable as the other foam boards but is commonly used as the insulating component of Structural Insulated Panels (SIPs) and stressed skin panels. XPS (R5 per inch) is sometimes referred to as Dow board and is usually blue or pink. XPS is a hardy, versatile foam board that is commonly used to insulate foundations and the exterior of wall assemblies. ISO has the highest R-value per inch (7) but this may be subject to a slight degradation over time. It is sometimes referred to as Thermax or High R board and always has a foil face on at least one side. This foil face can serve as an effective vapor barrier, making ISO a good choice for insulating on the winter-warm side of building assemblies.

Can insulation be used to air seal houses?

In most cases, insulation will do little to reduce air leakage. Insulation is primarily intended to reduce conductive, as opposed to convective, heat flows. This is especially true for fiberglass insulation. There are a few exceptions, however. Cellulose for example, can be installed in closed cavities at high pressure to help reduce leaks. Spray foam insulation such as Icynene also promotes airtight construction. Frequently, the additional cost associated with using these products is offset by reduced air sealing labor requirements. Even in houses where this strategy is employed, it is still important to address (seal) major penetrations around chimneys, ducts, plumbing stacks, etc.

What guidelines should I follow when installing fiberglass batts?

Fiberglass batts should be installed at full loft without any gaps or empty pockets. They should be installed flush with the face of the studs and should be cut to accommodate all obstructions (i.e. plumbing and electrical). If the batts are kraft or foil-faced, then the tabs on each side of the batts should be secured to the face of the studs, not "side-stapled." Fiberglass batts are typically installed incorrectly. To prevent this from occurring, specify the terms of installation at the time of design and make sure that bids are submitted accordingly. For more information, refer to our technical standards, or to information provided by the North American Insulation Manufacturers Association (NAIMA, publication #B1402).

What are ENERGY STAR windows?

The parameters for ENERGY STAR windows vary according to climate. In the Northeast, windows that have a Solar Heat Gain Coefficient (SHGC) of 0.55 or less and a U-value of 0.35 or less are generally labeled as ENERGY STAR windows. Always look carefully at the information provided on the NFRC stickers for the windows that you are purchasing.

From the standpoint of energy efficiency, what are the best windows currently available?

The best windows currently available are fiberglass-framed windows. Fiberglass-framed windows feature the highest ratio of glazing to frame area and consequently, the lowest U-values (as low as 0.15 for triple-paned units). The most energy-efficient windows also typically feature low-e coatings and argon gas.

What is the best window strategy to maximize passive solar gain?

The best way to maximize passive solar gain is to orient your house properly. The side of the house with the most glazing should face south. To avoid overheating, the glazing area on this side of the house should not exceed 7% of the floor area of the house (unless the glazing is coupled with thermal mass). In addition to having well insulated and airtight shells, passive solar homes that perform the best incorporate an appropriate combination of orientation specific, high performance windows, carefully designed overhangs, and sufficient amounts of thermal mass to store the heat during the day and provide heat at night.

For my current project, I want to use a large wooden entry door that I salvaged from an older home. Will there be any penalty for this?

The penalty for using an old, wooden door would probably be negligible. Most houses typically have small door areas compared to other components of the building. Consequently, the loads associated with doors are relatively small. These small loads can be even further reduced by making sure doors are airtight. Install quality weatherstripping and seal the gap between the door frame and the rough opening with either foam or caulk.

What are some important considerations when designing an HVAC system for an ENERGY STAR Home?

All ENERGY STAR Homes require a mechanical ventilation system. While there are many ways to satisfy this requirement, the simplest way is to install at least one bath fan that is rated for continuous operation. This fan should have a sone rating of 1.5 or less and should be operated in conjunction with either a 24-hour timer or variable speed controller.
Select high efficiency, ENERGY STAR rated equipment. Boilers with AFUE ratings of 85 or higher, furnaces with AFUE ratings of 92 or higher, and central air conditioning systems with SEER ratings of 14 or higher are preferable (visit www.aceee.org/consumerguide for a list of products). Domestic hot water should be stored in an indirect-fired tank (in cases where the house is being heated by a boiler) or generated by a hot water heater with an EF rating of 0.82 or higher.
Opt for equipment that features sealed combustion or direct venting. Atmospherically vented appliances should be avoided.
Insulate hot water pipes; seal and insulate all ductwork in unconditioned spaces.
Install programmable thermostats

Is one type of distribution system more energy-efficient than another?

The efficiency of a distribution system depends largely on the design and installation quality. Duct distribution systems are prone to the most significant losses–especially if the ducts are poorly sealed and/or installed outside the "thermal envelope" of the building (in an attic, for example). For obvious reasons, hydronic systems are typically installed within conditioned or "buffered" spaces like an unconditioned basement. In either case, it is important to insulate ducts/hot water pipes that are not in conditioned spaces. Theoretically, there is no difference in efficiency between one system and another. Radiant systems, however, generally provide higher occupant comfort levels at lower ambient air temperatures. This may result in lower operational costs. With radiant heat, it is particularly important to thoroughly insulate the cold side of the heated assembly.

What are the relative advantages and disadvantages of a furnace vs. a hydro-air system?

Generally, the first time cost of installing a furnace is much cheaper than the cost of installing a hydro-air system. The hydro-air system is more expensive because there is an extra component in the system (a separate air handler) and because boilers are usually more expensive than furnaces. Operational costs however, are generally lower for hydro-air systems (depending on the equipment selected). This is because Domestic Hot Water (DHW) can be produced by the boiler and stored in an indirect-fired tank. When a furnace is installed, it must be installed in conjunction with a stand-alone DHW tank. Stand-alone DHW tanks produce hot water at much lower efficiencies. These tanks also introduce an additional source of combustion and additional venting requirements to the system. If multiple duct distribution systems are specified for a single house, then the case for a hydro-air system gets stronger. In this case, the boiler would serve as a central heat "plant" with zones for each air handler and a zone for DHW. In this case, the first time cost might be similar to what it would cost to install multiple furnaces and the operational costs would likely be less.

What are the consequences of "oversizing" a heating and/or air conditioning system?

If a heating and/or air conditioning system is oversized, it will satisfy calls for heat and/or air conditioning quickly–leading to a condition know as "short cycling." When systems short cycle, they turn on and off frequently spending more time in start up/shut down modes and less time operating at peak, "steady state" efficiencies. The mechanical stresses that result from this may be more significant than the reduction in energy efficiency. These stresses may lead to increased maintenance costs and/or premature equipment failure. Heat/cool load calculations should always be performed to ensure proper sizing.