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Consider Installing Combination Heating Units


Question: My furnace is inefficient and the water heater is old, too. I might install a new combination hot water-space heating unit to replace both. Are they efficient and will there be enough hot water?

Answer: The answers are yes and yes. A combination system that produces hot air and hot water can be very energy efficient. Since the unit must have enough heat output capacity to heat your entire house, it can provide more hot water for morning showers than even the largest family could ever use.

Another advantage of a combination system is it can be used for warm floor radiant heating in one or more rooms. This is one of the most comfortable heating methods, especially in the morning.

Instead of having two completely separate heating units, one for air and one for water, it makes intuitive sense to install a single unit to do both tasks. A combination system requires only one contractor and fewer regular maintenance calls, produces less noise and often lowers utility bills.

The space heating portion is probably no more efficient than any other super-efficient gas or oil furnace. The big savings is for the hot water because the same efficient burners are used to heat the water too. This requires a smaller built-in hot water tank for less standby losses.

There are two basic types of combination systems: integral and modular. An integral unit heats the hot water and room air in one cabinet which is slightly larger than the typical gas furnace. A modular unit has a water heating unit that is connected by pipes to a separate air handler (blower).

In both systems, very hot water flows through a heat exchanger in the air handler. The blower circulates the room air through the heat exchanger where it picks up heat from the hot water. A central air-conditioning coil and air cleaner can be installed just like in any furnace or heat pump.

There are many types of air handler units made to fit almost any location and heating needs.

Smaller ones can be mounted inside a wall to heat only one room. Other whole-house models use efficient smart variable-speed motors for comfort. They use 75% less electricity than standard motors.

A high-output (gas, oil or propane) water heater is needed for a large house or an inefficient smaller house.

For an efficient house or one in a mild climate, an efficient, standard-output water heater often provides adequate heating capacity. Your contractor can size it properly for you.

If you are considering switching from expensive electric heat, consider a condensing system. It vents outdoors horizontally through a small plastic pipe without requiring a chimney.

For details, download Update Bulletin No. 934 at, a buyer's guide of 16 manufacturers of combination systems, new air handler units, super-efficient gas, oil, propane water heaters and a size-estimating chart.

Set Thermostat at Lowest Comfortable Temperature

Q: I just bought a clock-type setback thermostat for my gas furnace. It provides four temperature and time periods that I can set. How much should I set the temperature back at night and when I am at work?

A: There really is no recommended number of degrees to set it back. Set it as low as possible you when you are gone and at a comfortable level at night. You can probably lower it more at night as you get used to it.

The length of time that your furnace has to run depends on how fast your house loses heat. Heat loss depends primarily on the indoor-to-outdoor temperature difference, so a lower indoor temperature reduces this difference.

Increase Efficiency With Overhead Range Hood

Q: I have decided to get a range hood for my kitchen instead of just opening windows. My budget is limited. Should I get an overhead model or one that pops up from behind the range surface?

A: Any range hood is more efficient and effective than just opening a window. Opening a window loses too much conditioned indoor air and most of the grease vapor has already settled before it reaches the window.

An overhead model that you can find at most home center stores is probably your least expensive option. Overhead models also require less air flow than most down-draft (pop-up) models because hot air naturally rises.


Take an online tour of James Dulley's house and see the money-saving improvements and products that he tests. There are nearly 100 pictures with links to the various columns that describe the improvements and products. Go to on the Internet.

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