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When House Feels Too Hot
Contributing Solutions | Building Envelope and Duct Solutions | Air Sealing | Insulation | High Performance Low-e Windows | Duct Sealing | Heating and Cooling Solutions | High Efficiency A/COverview
It is common for a home to feel uncomfortably hot and stuffy, especially in the summer.
The walls, floors, roof, and windows form an envelope which protects the house from the hot outdoors and keeps cool air in. Most houses are poorly insulated and also have cracks and voids which let cool air leak out, and let hot air in. As the conditioned air leaks out of the house, hot and humid air is drawn into the house to replace it making the air conditioning system work harder to keep the home cool and comfortable. The problem is made worse when the air conditioner can’t get cool air to the house efficiently, due to poorly designed, installed and located duct work. This common problem can be solved by considering the home as a system
To solve the problem of an uncomfortably hot house all contributing root causes must be addressed. As with many systems, the whole is greater than the sum of the parts. For example, installing an efficient air conditioner and good insulation will do more to help keep a house cool when they are done together than if they are done separately. Here are the main things to be considered in a house which feels too hot:
- reduce the amount of cooling a house needs with air sealing and insulation
- help the duct system deliver the appropriate amounts of cool air to the house
- make sure the cooling system is working properly and well adjusted, since less cooling will be needed in a well insulated home
Building Envelope and Duct Solutions
These solutions should be addressed first to improve a home’s ability to retain cool air and to ensure that the ducts are delivering cool air to the rooms which need it instead of wasting it in the attic or crawlspace. The building envelope and duct system need to work together with the cooling system to make sure that the home stays comfortably cool.
- Air Sealing: A tight building envelope makes insulation more effective and helps stop the loss of conditioned air to the crawlspace and entry of hot air from the attic; this “reverse stack effect” is a primary driver of indoor air quality issues, draftiness and energy loss.
- Insulation: Added insulation will be much more effective in a well sealed home. Insulation slows the transfer of heat from the outside of the envelope to the inside, and the installation quality is vital for proper performance, comfort and energy efficiency.
- High Performance Low-e Windows: Well engineered and appropriately selected low-e windows can add additional insulation and air sealing benefits and block incoming radiant heat from direct sunlight before it enters the house.
- Duct Sealing: Properly sealed ducts will deliver more cool to the inside of the house instead of letting it leak into the attic or crawlspace. This effect will be compounded in a home with properly designed duct work with balanced airflow and minimal pressure imbalances between the rooms of the house.
Air Sealing
Air infiltration in typical houses is roughly equally split:
- 1/3 floors, walls, and ceilings
- 1/3 ducts, vents, plumbing penetrations, and electrical outlets
- 1/6 fireplaces
- 1/6 windows and doors. Source: EERE .
Gaps, cracks, and holes in all of these areas must first be sealed for insulation and heating and cooling systems to be effective. Air sealing helps homes that tend to overheat by stopping infiltration of hot outside air and by making the insulation more effective. [+] MORE
Insulation
The walls, floors, and roofs (which are generally poorly insulated) typically represent the largest surface areas in the house and therefor represent great opportunities for low cost improvements in a home’s performance. Insulating these areas first is generally more cost-effective than replacing old windows in an existing home, and therefore should be prioritized along with air sealing.
Properly installed insulation reduces heat gain and helps address uneven temperatures by minimizing temperature variability indoors and helps keep rooms cooler in the summer. [+] MORE
High Performance Low-e Windows
High performance windows save money due to improved insulation, reduced air leakage and improved solar radiation control. As an added benefit, high performance Low-e windows will also help protect furniture and fabrics from fading due to ultraviolet (UV) radiation. Source: energystar .
A poorly insulated window actually radiates heat toward the room when it is very hot outside. This makes sitting near such a window uncomfortable because it radiates heat directly to you even if the sun is not directly shining at you. Once a home has been well sealed and insulated, high performance windows can help remedy uncomfortably hot temperatures inside by reducing conductive and radiant heat gain from the sun. [+] MORE
Duct Sealing
Most duct systems suffer from the widespread problem of duct leakage where conditioned air escapes from gaps between the duct joints. Duct sealing, which is among the most cost effective of home performance retrofits, prevents conditioned air from leaking out of the ducts into the crawlspace and attic and also improves Indoor air quality at the same time by reducing crawlspace and attic dust from infiltrating the home directly through the return ducts or indirectly through pressure imbalances.
Duct Sealing can help keep a house cool by delivering more cool air from the AC to the home instead of wasting it in the attic or crawlspace. [+] MORE
Heating and Cooling Solutions
It is common to only think of a furnace when considering improving a home’s heating system. However, heating and cooling systems work together with the building envelope and duct system to deliver and retain warmth and cool to the home. For example, good insulation can be considered part of the cooling system since cool air that it retains is cooling that the air conditioner does not need to generate. High efficiency cooling systems such as energy star air conditioners can cost less to run, but they will be most effective at keeping a home comfortably cool when operating in conjunction with a well sealed and insulated building envelope, and with an effective duct system which doesn’t waste the energy used to cool the air.
High Efficiency A/C can help keep the home more comfortable with lower bills when they are sized correctly for the buildings cooling and dehumidification needs. Smaller units that run for longer durations are actually more efficient than if the same unit in a larger model were installed, because they require smaller motors and spend less time conditioning the evaporator coils instead of conditioning the house before each cycle. Properly sized air conditioners installed along with a well sealed and insulated building envelope and duct system will keep the house more comfortable by efficiently removing heat and excess humidity which makes a house feel stuffy with a slow and steady runtime as opposed to short cycling as oversize units do.
High Efficiency A/C
Replacing an old air conditioner with an energy star AC can offer increased comfort and lower energy costs when correctly sized and installed in a well insulated and air sealed home.
It is especially important to first improve the building envelope and duct system because doing so will generally mean a smaller air conditioner (which uses less electricity than an equally efficient air conditioner of a larger size) will be appropriate to cool the house. A correctly sized and calibrated system will deliver the right amount of cooling and dehumidification to the home. By staying on longer and cycling less often, a smaller system will increase efficiency and comfort by removing more moisture from the air. Homeowners must note that properly sized air conditioners are designed to turn on earlier in the day and run for long periods of time, because they will not be able to cool a house that has been baking in the sun all day without the air conditioner on.
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