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|HVAC & Water
Home Heating > Considerations
Capacity & Sizing
|Once you have an idea of the type of heating system that you prefer and a brand or set of brands that you trust, you then still have to narrow down the options further based on each product's capacity, feature set, and availability. This is not especially complicated, assuming you know exactly what you need. If you are not sure, this section should help.|
|Capacity & Sizing
It is important to size a heater appropriately to the needs of the residence. In the case of space heaters, sizing is not as important as the heating power will not vary as dramatically from one unit to another. However, for central heating systems, incorrect sizing can lead to a range of problems, including ineffective operation, unnecessary wear and tear, and high utility bills.
As mentioned, identifying the appropriate furnace size is important. An oversized furnace will be constantly turning on and off, which is referred to as “short cycling” and leads to efficiency losses and increased likelihood of heat exchanger breakdown. On the other hand, an undersized furnace will be running too often and may not provide sufficient heat during the coldest days of the winter season.
Properly sizing a furnace requires understanding the space configurations and requirements of the residence. Detailed sizing calculators may be found online, free of charge. Service providers who will be assisting with the purchase decision and doing the system installation can also compute the necessary BTU rating. Finally, a general approximation can be used based on the climate zone and square footage of the residence, although it is not a substitute for a detailed calculation.
For residences located in the southern-most states, which are those that border on Mexico or the Gulf of Mexico, the estimate is 35 BTUs multiplied by the square footage of the home. For residences located in the middle of the country, stretching from Nevada, through Kansas, and onto Maryland, the estimate is 45 BTUs multiplied by the square footage of the home. Finally, for residences in the northern-most states, which are those that border on Canada or the Great Lakes, the estimate is 55 BTUs multiplied by the square footage of the home. Since most furnaces are manufactured using increments of 20,000 BTUs or 25,000 BTUs, a ballpark estimate can be a relatively accurate predictor of the necessary furnace capacity.
In the case of heat pumps, the sizing is typically performed using the pump’s cooling capacity rather than its heating capacity. In this way, the sizing calculation is similar to that for air conditioning systems. Again, detailed calculators are available, but a general rule of thumb is to add 1 ton of capacity (equivalent to 12,000 BTUs) for every 500 square feet of the home. Thus, a typical 2,000 square foot residence will require a 4-ton cooling capacity heat pump.
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There have been a number of innovations which are making both heat pumps and furnaces more energy efficient, powerful, dependable, and user-friendy. With respect to heat pumps, one such innovation is two-speed compressors. These allow the unit to run on one of two stages, depending on the thermostat setting versus the current temperature in the home. The ability to cycle to a lower stage when possible, allows the unit to attain much greater energy savings and provide more operational flexibility. Two-stage heat pumps are also better at working with zone control systems, which allow different rooms to be heated to different temperature levels.
Similar to two-speed compressors for heat pumps are multi-stage burners for furnaces. These allow the furnace to operate at different levels of power usage, adjusting the furnace in real time based on the heating needs inside the home. By allowing the furnace to run at a lower level of power usage whenever possible, multi-stage burners result in lower energy usage and greater longevity for the system.
Another feature to consider are variable-speed motors for the blowers. These are available for both heat pumps and furnaces. By being able to automatically ramp up or down individual blowers, such systems provide a more even distribution of warm air throughout the home, largely eliminating cold drafts and air pockets that are relatively warmer or colder than the rest of the room. Variable-speed motors also reduce blower noise and improve energy efficiency.
Certain heat pumps also feature what are known as scroll compressors in place of traditional piston compressors. These have been shown to provide more consistent function, a longer operating life, and a reduced noise level. In addition, scroll compressors increase the maximum heating capacity of a heat pump by up to 15 degrees Fahrenheit, which is particularly valuable in colder climates.
Speaking of colder climates, one of the key drawbacks of an air-based heat pump is its dependence on the availability of heat in the outside air. On especially cold days, such a heat pump may not be able to provide the necessary level of heating. One solution for this is to purchase a heat pump system which incorporates back-up burners, which essentially act as a furnace-type addition to provide heating when there simply is not enough
warm air outside for the heat pump to operate effectively.
With both heat pump and furnace systems, another innovation is the incorporation of intelligent controls. Such controls allow for the dynamic monitoring of temperatures and humidity levels in different parts of the home, automatic adjustment of zoning systems and airflow, filter tracking, and remote access of real-time data pertaining to your home.
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Buying a space heater is far easier than purchasing a central heating system. Since there is no installation, space heaters are a one-stop purchase. As a result, they are widely available and may be found at a broad range of retail and online sources. Not every supplier will carry every type and every brand, however.
Most of the large hardware store chains carry space heaters, including Home Depot, Lowe’s, Orchard Supply Hardware, and Menard’s. Many big box stores have them as well, including Wal-mart, Sears, Target, and Costco. However, the sales personnel may not necessarily be knowledgeable about the specific products, so it is best to go in prepared and know the type of space heater that is desired.
Alternatively, space heaters can be purchased online through either an HVAC or hardware product e-commerce site, or through one of the major marketplace sites such as Amazon, Buy.com, Nextag, and others. The benefit of buying online is that comparison shopping is easy and, generally, the best prices are available online. However, if buying online, you should make sure that you are purchasing from a reputable source with a proven track record of excellent customer service and a guaranteed return policy for defective products.
In the case of a heat pump or furnace, the situation is more complicated. Most consumers purchase their central heating systems through an HVAC contractor or service provider who also handles the installation. The advantage of service contractors is that they have extensive expertise in the field of home heating and can provide a lot of useful information.
However, many service contractors are loyal to a limited number of brands. In some cases, service providers are authorized dealers for only a single brand. Consequently, a service provider may pressure you to buy a particular brand or type of product rather than offering truly objective information. For this reason, it is vitally important for you to do your own homework and develop an idea of the type of heating system and brand name that you would prefer before you begin to have detailed conversations with local service providers.
Pricing also varies widely among different service providers, not only in terms of the labor and parts for installation, but also in terms of the sticker price for the heating system itself. Once again, getting at least four quotes should be mandatory. Given the high costs of central heating systems and their corresponding installation, this is not that different from buying a car. Just as a consumer would typically want to visit multiple car dealerships before making a purchase, so should a consumer evaluate multiple HVAC service providers before making a final choice.
In recent years, it has become possible to also directly purchase furnaces and heat pumps online from distributors and authorized resellers. However, there has to be a lot of research done before this avenue can be safely pursued. You should know exactly what type of system you want and need, whether it will require auxiliary components such as ductwork, and what types of guarantees the distributor is offering.
Generally, you should not make any purchases without first finding a trustworthy local contractor and receiving an opinion regarding whether the system is appropriate for your residence, what the installation process will entail, how much it will cost, and whether there may be more cost-effective alternatives.
You should also be wary of deals that sound much too good to be true. If an online seller is offering a particular furnace or heat pump brand model for $1,000, but it costs $2,000 or more everywhere else, further investigation is necessary before making a purchase commitment. The seller may be trying to substitute a non-brand product for the brand name, or selling a different product than advertised altogether.
A high quality local service provider should be willing to work with and accommodate, to the extent possible, your preferences as far as type, brand, and model of central heating system. As part of the due diligence process, you should ask to see examples of prior work or, barring that, at the very least a list of recent customers who would be willing to give the service contractor a reference.
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