MORE AT This Old House
If you're considering a new system for your home, talk first to your architect or designer. Conversations with HVAC contractors will probably follow, although you or your designer may also want to consult a specialist – a heating engineer – in the event your building project presents unusual demands.
Talk through in detail exactly what your needs are. If your budget is tight, you'll need to identify essentials. If you can afford to think more broadly, consider the added comfort of, say, radiant floor heating. If you're unhappy with your present system or would like to add humidification or a filtration system, get bids for those costs. In most cases, extending your existing system or adding a smaller area heater will be the least expensive option.
Here are a few other considerations:
The Air-Conditioning Option. As a rule of thumb, if local temperatures rarely rise above 85 degrees Fahrenheit, you probably don't need central air-conditioning. On the other hand, central air is often regarded by realtors as a valuable selling point, so if there's a chance you'll be transferred to another region or are likely to put your home on the market for any reason in the near future, central air-conditioning may be a good investment. Top-of-the-market houses get top-of-the-market prices because they have all the bells and whistles. For people with asthma and other allergy problems, central air with its ability to filter and "condition" household air can also have health benefits.
Beware of Oversize Systems. Strange though it may sound, too much heating capacity will make a system less efficient. It will cause the system to cycle on and off frequently, producing excess wear and tear on the components. The system may never reach peak operating temperatures.
To be sure your system is suited to your home, ask your HVAC contractor, heating engineer, or whoever designed the system to walk you through the calculation. The process consists of determining what the heating load is (based on an arithmetical formula that factors in the size of your home, its insulation, and the local climate). The system capacity should be no more than 25 percent greater than the calculated heating load.
Simple Is Usually Less Expensive. Staying with your existing system is almost certainly the cheapest route. If your system has enough capacity that it can be extended to heat (or cool) new spaces, that approach will probably be less expensive than installing an all-new system.
Buy Quality. Good shoppers don't always buy bargains. Buying durable boilers or furnaces that come with long warranties often costs more initially but, over the years, presents fewer headaches. Good furnaces often are guaranteed for twenty years, boilers for thirty, heat pumps for less.
Think Locally. Don't buy equipment that no one in your area can service. If the only HVAC contractor who'll bid your job is a long-distance call away, you could be asking for trouble. These sophisticated modern systems require occasional checkups by service people familiar with their design, installation, and individual characteristics. One industry study found that half of all service calls were the result of improper or insufficient maintenance.