Furnace too big?

[Seasider]

About 6 years ago, I bought a new house. As part of the renovating process, I had a Home Depot contractor put in a new furnace in which also allowed central air conditioning to flow through the same vents. For a little over 5 years both A/C and heat seemed to work just fine but then at the end of last winter, the furnace started blowing nothing but cold air. At the time it was not a major concern as winter was pretty much over. When Fall came around, we had another heating contractor examine the furnace. This guy immediately pointed out that the furnace was too big our house. He went ahead and replaced the filter and did whatever he needed to do to get the furnace generating heat to the house again. 2 weeks later, the problem was back. The guy comes back and now says in order to fix the problem, they'll need to redo all the duct work because basically they can't handle the oversized furnace. Obviously, that route will not be cheap but I'm puzzled at frustrated at what to do. It just doesn't make sense to me that something that worked for 5 years would be the result of it being the wrong one for my house. Any input or advice would be greatly appreciated.

[HayZee518]

was any sort of maintenance done on the unit on an annual basis? I mean besides filters? check freon, oil bearings on blowers, check combustion if it was gas, check heat exchanger for cracks. It seems highly unlikely that its oversized because it functioned for 5 plus years. anyway its a little late to downsize the trunk lines or the unit.

[paul52446m]

About 6 years ago, I bought a new house. As part of the renovating process, I had a Home Depot contractor put in a new furnace in which also allowed central air conditioning to flow through the same vents. For a little over 5 years both A/C and heat seemed to work just fine but then at the end of last winter, the furnace started blowing nothing but cold air. At the time it was not a major concern as winter was pretty much over. When Fall came around, we had another heating contractor examine the furnace. This guy immediately pointed out that the furnace was too big our house. He went ahead and replaced the filter and did whatever he needed to do to get the furnace generating heat to the house again. 2 weeks later, the problem was back. The guy comes back and now says in order to fix the problem, they'll need to redo all the duct work because basically they can't handle the oversized furnace. Obviously, that route will not be cheap but I'm puzzled at frustrated at what to do. It just doesn't make sense to me that something that worked for 5 years would be the result of it being the wrong one for my house. Any input or advice would be greatly appreciated.

It sounds like he is not finding what is wrong. If the furnace was too large for the house and too large for the ducts. The furnace would just heat up fast,
turn burner off on limit and wait for the blower to get rid of the heat before
it came on again. It is not good for a furnace to run like this because it keeps over heating the furnace and that will shorten the life of the furnace.
Most furnaces have a 70 to 80 degree temperature rise across the heat exchanger, so if air going in is 70 degrees , the air come out should be 140 to 150. Usually the limits are set a 180 degrees.
To check furnace size and duct size you would have to do a complete heat loss on the home. How many sq. foot is your house, what size is the furnace
where do you live, how cold does it get in your area? later Paul