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rustbucket
Electric Furnace Question

I have an electric furnace just for my garage with out any duct work just one vent on top on a 3 foot stack on top of the handler. The air comes out hot at first then gets cold very quick.

I have been told this is due to static pressure. Can you explain? Is this normal? What can be done to fix this?

canuk
Re: Electric Furnace Question

An electric forced air furnace is basically the same as any other forced air furnace ..... difference being using electric heat strips instead a flame.

Basically there is a ( cold ) air return ..... which supplys the air to the blower and blows the supplied air across the elements to be heated and is forced out at about 100 degrees .

Lets say the air temperature inside your garage is 30 degrees.

There needs to be a delay to allow that 70 degree difference to occur .... it can't happen immediately.

When a furnace is installed with ducting in a home ... the ducting creates this delay by static pressure. The calculated amount of resistance the ducting provides results in pressure (resistance).

In other words .... in your case if the temperature is cold and you pass the air too quickly over the heat elements .... it won't have a chance to heat up very much.

You could try and reduce the opening of the return supply or reduce the blower speed to reduce the air speed.

The other side of the coin is .... if the air moving over the heating elements doesn't move heat quick enough this may cause a high limit control to shut off the elements . The high limit is a safety feature of a furnace.

Just a thought.

JLMCDANIEL
Re: Electric Furnace Question

I would think with the setup you have it might be better to control the fan with a temperature sensor so it only comes on when the temp inside the furnace gets hot. Convection alone may work 90% of the time.
Jack

Fencepost
Re: Electric Furnace Question

The furnace will provide the same amount of heat regardless of static pressure (and therefore air speed) in the ducting. The only difference is that the air coming out feels cooler to you; it will still heat your shop in the same amount of time (if not sooner) as it would if it had a bunch of ducting.

It's simple, really: a 6,000-watt resistive element always puts out 6,000 watts of thermal energy. If it takes 6 killowatt-hours of energy to heat your shop, it will take a 6,000 watt heater one hour to heat your shop. Period. No matter how fast the air is moving over the element. (You didn't say the size of your furnace. I'm just using 6,000 watts as an example.)

So as the others have posted, it feels cold because the air is moving faster over the element and doesn't have much time to heat up. But rest assured that it IS heating up, and your shop will warm up eventually. Adding ducting or a restrictive vent, while it may make the air feel warmer, and it may make YOU feel warmer, it won't warm up the garage as a whole any quicker. (Well, it might, ever-so-slightly. Having the air moving quickly may increase conductive heat loss through the walls and windows. But you're still getting the same amount of heat from the furnace.)

If you don't like the cold draft, direct the airflow to somewhere you're not working.

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