oversized undersized heating system

[grumpydasmurf]

What can occur if a system is oversized, what can occur if the system is undersized?

[Rich]

Heating over/under is not as big a deal as if the a/c unit is over/under. If it's undersized it will take longer to heat the home to the desired temp. If it's oversized it will take less time.

[roger g]

Well................. there is a little more to it.If you have a high efficiency furnace , and everyone should or thinking about getting one, being oversized is not good. Most furnaces are extremely oversized because everyone factors in huge fudge factors. I'm talking about heating now. If you buy a high efficiency furnace i would assume that you want it to run efficiently. Probably highly efficiently. Like with anything mechaniclal they run more efficient at specific periods or times or conditions. If you oversize it then it is not doing it's job........ efficiently.
It's like having a fuel efficient car where you stomp on the gas till it red lines then you coast then stomp on the gas again. You stillget to your destination but it cost you more in fuel.


roger

[Rich]

You're right roger in principle - good analogy with the car efficiency. The reason I specified a/c more than furnace is the difference between electrical costs and it's efficiency compared to natural gas efficiency before it ever gets to the efficiency of the unit itself. Typically you will spend much more during the summer than the winter.
Not to say that one is more important than the other because I sure like to be cool in the summer than warmer in the winter. :)

[grumpydasmurf]

Actually the answer I was looking for was uneven tempratures, frequent on/off, or with ac massive condensation.

This was for a final exam for a class and I waited to the last minute :) Anyways that's what the book claims will happen.

[roger g]

Always keep your furnace on continuous fan . It keeps the air from layering which means your feet should be the same temp as your head. The air doesn"t stagnate as much. The air is constantly cleaned. All in all it is much more comfortable living.
The very best way of doing it is to have two duct systems. One for heating and the other for heat, Usually the furnace and the ductwork run down the centre of the house because we like things symetrical. Big problem with that though. In the winter the north side and the west side of the house are usually the coolest and that is where the majority of the heat should go. ( to the main source of the cold) But in the summer the hottest part of the house is on the south side where the heat is. By having everything equal the north side of the house is cooler in the winter and in the summer the south side is always warmer but you crankk up the cooler to cool that south side room just great but the rooms on the north side are too cold In summary you should have bigger ducts going to the north side for heating and bigger ducts on the south side for cooling.

roger