ISU Extension Publication #: AEN-169
Author: Dr. Thomas Greiner, Dept. of Agricultural and Biosystems Engineering
Iowa State University
Date: 7/96
What should I consider when buying a new heating appliance?
When purchasing a gas or wood furnace, boiler, water heater or fireplace, the main factors to consider are safety, purchase cost, operating cost, maintenance requirements, comfort level, dealer support, and indoor air quality.
Has buying a new appliance changed in the last decade?
Definitely. Houses are now much tighter. Heating equipment designed to operate in loose houses may not operate properly in tight houses. A decade ago most appliances obtained air for combustion and venting from the interior of the house. Leaks in the house replenished air lost up the chimney. Not only do tight houses not have enough air leaks, there are often more exhaust fans competing for air.
What happens when there is insufficient combustion and venting air in a tight house?
The house becomes depressurized. This causes downdrafting in the vent (chimney), and the products of combustion remain in the house. Carbon monoxide in the flue gases spill into the house. Lack of adequate combustion air increases the rate of carbon monoxide production, making the problem worse.
How dangerous is this?
The products of combustion from fossil fuel fired heating appliances cause several hundred deaths and thousands of health complaints each year. Continued exposure to carbon monoxide can cause permanent brain, nerve, or heart damage. Some people require years to recover while other remain permanently incapacitated.
Is there a solution?
For anyone purchasing a new heating appliance, the solution is relatively simple–purchase only sealed combustion direct vent heating appliances or use electric heat. Direct vent units obtain combustion air from outside the house, and are less likely to allow the products of combustion to remain in the house. Because of the sealed design and forced exhaust flows, downdrafting does not occur. Extra safety switches ensure that venting is occurring before the burner will ignite. Furnaces, boilers, water heaters, and fireplaces are available as sealed combustion models.
Besides air quality, are there other advantages to sealed combustion units?
Sealed combustion units deliver more heat more efficiently at reduced costs. Houses can remain tight and draft free since combustion air is not pulled into the house through cracks. And the units vent through plastic pipes making them easy to place anywhere in the house. Sealed combustion units are usually top-of-the-line units, with better materials, longer life, and less maintenance.
Are there disadvantages to sealed combustion?
The initial cost is higher. With inexpensive fuel it may take several years to recover the cost. Since sealed combustion does not remove air from the house, there may be a need for additional ventilation.
Where do I go for more information about sealed combustion heating systems?
Find dealers you trust, then comparison shop. Manufacturers now offer sealed combustion furnaces, boilers, and gas-fired fireplaces. Sealed combustion water heaters and wood-fireplaces may be harder to find, but are available. Newly developed innovative units, combining a hot water boiler, water heater, and forced air heating system, are now available. Ask to see efficiency ratings and warranties.
How do I know which fuel to use?
All fuels can be safely used. During the heating season it takes from 100 to 150 million Btu’s to heat an typical Iowa home. Use the following worksheet to determine approximate costs to put one million Btu’s into a house. Check local fuel prices and enter them in column 2. Make sure the figures correspond to the units listed in column 2 (gallon, kilowatt, cord, etc.). Column 3 lists typical efficiencies for existing equipment. If you know the system efficiency, replace the given figure with the actual efficiency. Multiply column 1 by column 2. Divide the result by column 3. Put this figure in column 4. Column 4 shows the cost of putting 1 million Btu’s of heat into your house, using a specific fuel.
| Fuel |
#1 Quantity for One million Btu’s |
#2 Fuel Price |
#3 Annual efficiency |
#4 Fuel cost per million Btu’s |
| Natural Gas | 10.0 Ccf | x $_________ per CCF |
/ 0.60 or_________ |
= $ |
| LP Gas | 11.11 gal | x $_________ per gal. |
/ 0.60 or _________ |
= $ |
| Electricity (resistance) | 293 Kwh | x $_________ per Kwh |
/ 1.00 or _________ |
= $ |
An example:
| Fuel |
#1 Quantity for One million Btu’s |
#2 Fuel Price |
#3 Annual efficiency |
#4 Fuel cost per million Btu’s |
| Natural Gas | 10.0 Ccf | x $0.61 per CCF |
/ 0.60 or_________ |
= $10.17 |
Should I use unvented appliances?
Even when burning clean, unvented heating appliances produce water vapor, carbon dioxide, nitrous oxides, and other undesirable combustion products. To obtain the best indoor air quality these gases must be vented or exhausted outdoors.In summary, to reduce the risks of downdrafting and carbon monoxide poisoning and to improve indoor air quality, purchase only sealed combustion direct vent high efficiency heating appliances. As well as improving the air quality in your home, you will reduce heating costs and increase comfort.
For more information request other notes in the Carbon Monoxide series. Agricultural Engineering Notes (AEN’s) are informally published information releases on topics of current concern to Iowans.