can i install dual fuel in plastic wrapped older home

Mike G_3

Yes, by "dual-fuel" i'm talking about a heat pump with an LP backup furnace. Since I built the house in 1976, I've been told by many people that you can't use a gas furnace in the vapor shield wrapped house or condensations will be so severe that it will rot ceiling joists. I've heard of people having done it anyway and having pools of water in their attic. Not having seen it with my eyes, i've always been skeptical. My home is in the country so natural gas is out of the question.

Mike G_3

Can I install dual fuel in plastic wrapped older home

My home was built in 1976. I need to replace the original heat pump systems (2). The house was wrapped with plastic vapor barrier. Will a dual fuel furnace using LP gas rot out my studs and ceiling joists? I want warmer and cheaper heating. Thanks! Mike

John Mills_4

I'm confused

What would cause your studs & joists to rot out?

Price fuels but normally you can't get much more expensive than LP. Staying all electric may be a cheaper heat! A good heat pump with electric backup and a good electronic thermostat on a good duct system isn't that bad.

Mike T., Swampeast MO

If I remember my late childhood properly, there were some VERY tight, rather "experimental" houses built around that time. I would NEVER consider ANY form of unvented combustion heater in such a house!

All true "furnaces" I know of have a flue to the outdoors and are thus incapable--under normal circumstances--of adding humidity (via water from combustion) to the house. If your house is very tight, I would suggest use of a WELL SEALED, "balanced" heating appliance that draws its combustion air from the great outdoors. These tend to be more efficient. Otherwise, you may well need to make a literal "hole in the wall" to ensure proper combustion air.

What sort of "dual fuel" appliance are you considering? If something weird like solid (wood, coal, etc.) and gas I HIGHLY suggest that you contact your insurer BEFORE installing such an appliance INSIDE the house. High fuel prices tend to bring out some really kooky ideas--often installed by kooks with ZERO business EVER touching the combustion end that can not only endanger the structure, but the occupants. Many insurers will drop you INSTANTLY or deny a claim if you install a solid fueled space heating appliance inside the house. When I changed homeowner's insurance a few years ago, the insurance inspector utterly insisted that I show him--not just tell him--that I wasn't using solid fuel in my big old house with radiators. Of course he got a lot more information than he really wanted when I started talking about my Vitodens 200 hanging on the wall...

Mike T., Swampeast MO

Were they perhaps talking about ventless gas heaters? If so, I would NEVER consider using one in a tight home. Those things are far too popular in my area and even in old, leaky homes I can smell them (and see the soot on the ceilings/walls) the instant I walk in.

A properly functioning, vented gas furnace is incapable of either adding or removing moisture from the air it heats as the flue gasses and the room air are completely separate. They do however lower the relative humidity of the room air--the hotter the air they produce the lower the relative humidity, thus leading many to believe--even feel--that they "dry out" the air.

Perhaps the people you've been talking to used humidifiers. When malfunctioning or improperly set these can lead to severe condensation problems. When humidifiers are used, you are supposed to lower the setting as it gets colder outside. Few people bother--often to the detriment of their homes. Some humidifiers have truly automatic controls that handle this adjustment for you, but they're rather expensive and I'm nearly positive they have to be connected to an outside temperature sensor.

SteveD

your vapor barrier

If your vapor barrier is properly installed on the inside of the studs (behind sheetrock) you should be OK, rot-wise. If the house is wrapped on the outside you are in trouble no matter what you do.

The point of the barrier is to keep the vapor from the cold, condensing temperatures in the wall. Vapor barrier on the outside will be a mold and rot nightmare as the insulation and studs get soaked.

World Plumber

Condensation rotting studes

A properly vented high effencency Gas furnace will not add any moisture to your home. The condesation from combustion goes out the vent. You can get units that are 96 to 97 % effencent today. Nonvented brick and space heaters will rot your house out as well as cause health problems. On a nonvented unit all the water from combustion goes into the air in the house as well as all the carbondioxide. In our area the gas company will not supply gas to your home if you install a nonvented unit and they find out. They will give you 5 days to remove it if not done they turn the gas off. Do you have many days below 40 degrees each year? Check out your heating degree days. If you don't have a lot of supper cold days it may cost you more to run. If you install a furnace. I suggest the Honeywell Vision 8000 or IAQ thermostat for your dual fuel control.