Old-House Climate Control

Clear guidelines on whole-house systems, heat pumps and minisplits, high-velocity retrofits, and ways to boost comfort.

There’s more than one wayto create whole-house comfort, even in older homes without ductwork. The small vents from SpacePak’s mini-duct system,which deliver warm or cool air, all but vanish intothe ceiling.

Whether indoors or out, we humans like to live in temperate situations. Weather and seasons, of course, vary in the extreme: from arctic cold to Louisiana hot, from dry as a desert to wet as a steaming bog. Sunlight in some locales is a significant factor in cooling; in other places, abundant cloud cover creates different conditioning needs and makes certain technologies less relevant.

HVAC Whole House Systems

There’s no one solution to overall indoor temperature comfort, certainly not one that works as well in Connecticut as it does in Arizona. That’s the key reason why different HVAC technologies are more popular in some areas and nonexistent in others. For instance, steam and hot-water radiant heating emerged well over a century ago in the cold Northeast, while forced-air heat pumps have been the standard in the South and West, for decades, given their ability to supply and circulate both warm and cold air.

The difficulty of balancing the need for heating and cooling during weather extremes has led many homeowners to install overlapping systems: a fireplace insert to boost an older furnace, say, or window air conditioners in a house with steam radiators. This has resulted in the expansion of HVAC-related industries in everything from spot radiant heating to solar panels.

While any of these options can have a place in a well-thought-out approach to increasing the comfort of your home, it’s best to evaluate the needs of the house as a unit first. Even if you think your existing HVAC system is working well, it may pay off in the long run to have it evaluated for efficiency. If an addition or major renovation is in the planning stages, now is the time to consider an upgrade to newer, more efficient heat/cool sources, or even conversion to a completely new system, such as geothermal.

Whole-house systems generally consist of a boiler or furnace and the pipes or ductwork needed to deliver the heated and/or cooled air to different rooms in the living space. No matter what kind of system you have or what fuel you use, it’s imperative that the boiler or furnace be maintained in peak condition and properly sized for the house. Have it professionally checked once a year by your power supplier or an HVAC contractor. (The Department of Energy has a maintenance checklist, too long to repeat here, at energy.gov/energysaver/home-heating-systems/furnaces-and-boilers.) If the existing boiler or furnace is over 20 years old, it’s usually worth the cost of replacement to lock in future savings on heating and cooling bills.

Determine what’s readily available in your area, if you are considering changing fuels as part of an energy upgrade. Then get estimates from a qualified heating-and-cooling contractor and local utilities, regarding what you can expect for operating costs now and long-term.

Efficiency is another key consideration. Modern boilers and furnaces display an Annual Fuel Utilization Efficiency (AFUE) rating. New residential boilers must have an AFUE rating of at least 80 percent (85 percent to be EnergyStar rated). By comparison, many old boilers have AFUEs between 50 and 70 percent, making them much less efficient than newer models. The higher the AFUE, the more efficient the boiler. To further boost the efficiency of the boiler, look for a unit with a modulating aquastat. Aquastats are controllers that adjust the boiler water temperature based on outdoor temperatures, reducing operating costs and improving indoor comfort.

In a mini-split system like this one from Mitsubishi Electric, the heat pump is installed outdoors, powering one or more of the indoor units. 

An emerging idea in boiler technology that should adapt well to the tighter spaces in older homes are condensing combination (or “combi”) boilers. In a technology similar in concept to tankless water heaters, these high-efficiency boilers heat water on demand and also separate the lower-temperature water for residential use from the super-heated water used for space heating (through a hot-water baseboard system, for example). Although the technology is proven in institutional and commercial settings, the industry has experienced maintenance issues with units intended for the residential market. As part of the next generation of combi units, Lochinvar just introduced the noble Fire Tube Combi. The noble places critical components like the built-in circulator in an easily accessible location within the unit to simplify maintenance.

As with boilers, furnaces are rated for efficiency with an AFUE. Minimum efficiency furnaces generally have an AFUE rating of about 80 percent. Fine for milder climates, the best offer electronic ignition instead of standing pilots, better heat exchangers, and internal vent dampers that reduce the loss of heated or cooled air when the unit isn’t cycling. Mid-efficiency furnaces (83 to 87 AFUE) offer more precise control of combustion and venting. If you are burning oil, look for a furnace that has a high-static burner; it will extract more heat from the fuel. High-efficiency furnaces—recommended for large houses or homes in areas with extreme heating or cooling demands—have AFUEs in the 90 to 96 percent range. High-efficiency furnaces incorporate a second heat exchanger to reclaim some of the heat lost through vaporization.

For boilers and furnaces, specify a sealed combustion unit, which brings outside air directly into the burner and exhausts combustion gases directly to the outside, eliminating the need for a draft hood or damper. Also, take electricity use into consideration. Boilers use electricity to power circulating pumps; furnaces use it to run the fan motor. For a boiler, look for a unit with high-efficiency pump. Similarly, for furnaces, variable-speed or multi-speed fan motors are usually more efficient than single-speed motors.

Recommended insulation levels are identified by zone for the entire country; the higher the number, the greater the amount of insulation needed to achieve desired R-value.

Insulation & Radiant Barriers

No matter where you live, a well-insulated house will be more comfortable, whether the outside temperature is 9° F or 90° F.

Insulation helps balance the need for additional heating or cooling during weather extremes. The higher the R–value of the insulation, the greater its effectiveness. The Department of Energy publishes a guide to recommended insulation levels by location based on R-values, available online at energystar.gov.

Installing more insulation in your home usually increases the R-value and the resistance to heat flow. With retrofits, however, this value can be affected by temperature, aging, moisture accumulation, and the settled density of the insulation, so it’s important to take those factors into consideration when installing additional material.

If the house is in a particularly hot climate—Zones 1, 2, or 3, for instance—installing a radiant barrier is key to improving overall comfort, no matter how much insulation is in place. Although radiant barriers have no R value, these highly reflective materials re-emit radiant heat rather than absorbing it, reducing cooling loads.

Sizing a boiler

A boiler that’s too small won’t be able to produce sufficient heat to warm the house, and one that’s too large will waste energy. A boiler’s output is measured in BTUs (British Thermal Units). To calculate the correct size, use these guidelines:

Cold climates: 50 BTUs per square foot

Moderate climates: 35 BTUs per square foot

Warm or hot climates: 20 BTUs per square foot

If choosing between boilers that are slightly larger or smaller than the suggested BTUs for the square footage of your house, always go with the larger option. Otherwise, you’ll be looking at supplementary heating methods.

Pro Tip: Heat pumps are rated by heat seasonal performance factor or HSPF. The higher the HSPF, the lower the annual heating energy cost. The minimum HSPF rating for air-sourced heat pumps is 8.2. High-efficiency models are rated at or above 9 HSPF.

 Already inconspicuous, mini-duct vents can be dressed up with trimwork that accents or conceals their presence, as shown by these designer vents from Hi-Velocity.

Heat Pumps and Mini-Splits

Another common whole-house system for moderate and warm climates is the air-source electric heat pump. Primarily driven by the need for air conditioning, a heat pump uses a refrigerant to cool the house during warm weather. When it’s cold out, the pump can reverse the cycle to heat the house. Surprisingly, heat pumps can be more energy-efficient than other types of electric heat, including gas furnaces.

A more recent type of heat pump, called a ductless or “mini-split,” is an ideal retrofit option for homes with no existing duct system. Multiple wall-mounted indoor units can be installed in individual rooms, all connected to a single outdoor unit. Like any heat pump, this type can provide both heating and air conditioning, but without the expense and destruction of installing a duct system. Many if not all ductless systems are Energy Star certified and can cut heating and cooling costs by up to 30 percent.

Geothermal systems powered by heat pumps are even more efficient, because they absorb heat from either the ground or from water pumped from below ground.

Invisible Cool

When an HVAC update is mandatory but it’s essential not to disturb the walls or the plaster, there is a whole-house option: mini-duct systems, offered by companies such as Unico, Space Pak, and Hi-Velocity. These cleverly conceived HVAC delivery systems consist of flexible, mini-duct tubing small enough to be routed between studs in walls and in cavities under floors and above ceilings, powered by an air handler. Tubes a mere 2″ wide send
high-velocity air throughout the house by aspiration, producing relatively even heat or cooling from floor to ceiling.

The system creates a gentle circulation pattern and, unlike some forced-air systems, is very quiet. Mini-splits are also an excellent way to add air conditioning to a house with a functional heating system but without the large ducts required by traditional air conditioning.

Towel warmers, like this wall unitfrom Runtal North America, can put out such a significant amount of heat that they also work as room radiators.

A Little Boost

Some of the best innovations in heating and cooling come in small packages, and offer other benefits: Towel radiators double as towel racks and warmers. Fireplace inserts create cold-weather ambiance as well as abundant heat. Storm windows block sound as well as heat loss.

Other options replace units that have become obsolete, worn out or broken, or are simply missing. Stiebel Eltron’s electric convection wall heater is an energy-efficient replacement for old electric baseboard heaters; Runtal North America’s style-sympathetic Steamview radiators can fill in the gaps in a one- or two-pipe steam heating system.

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