Help with oversized furnace causing short cycle

Question

I have just moved into a new home that had a pretty terrible HVAC system installed brand new by a flipper which has been causing me a ton of headaches.

My house is 2000 sq feet, and the furnace is in the attic. They have currently installed a 130k Payne furnace, and matching air conditioning unit.

There are 4 registers in the upstairs (3 bedrooms / bathroom) right below the attic.

Originally there were 5 registers downstairs, and the return is at the top of the stairs along with the only thermostat.

When I first moved into the house I immediately noticed something was wrong since it the thermostat was reading 68 but it felt incredibly cold downstairs. I had someone come in and they basically told me the whole job was a mess and clearly it was severely broken.

I then had the following work done to try and correct the issue:

1. Install ecobee thermostat so that I could have it pretend the thermostat is downstairs. This makes it warmer downstairs BUT makes it inferno like upstairs since airflow going downstairs was bad and upstairs was very strong.
2. Install 3 additional ducts going downstairs and adjust the main trunk into 2 trunks so that one day I could zone (no zone dampers installed yet)
3. Install a duct going down into the basement to get more air away from the furnace / upstairs
4. Install 5" media filter in the attic so that I don't die trying to replace a filter on the ceiling of a staircase

After the work was done there was a significant improvement. Now it only takes about 15 min to go up the 1.5 degrees downstairs when the thermostat clicks on. However, the system still has problems and I'm not sure where to go next. Current problems are as follows:

1. Any day it is around 50 degrees or more the furnace will short cycle. Highly annoying because it will be off for 3 hours when this happens
2. It is still way to hot upstairs under most circumstances. I was advised to close the dampers at least half way or more upstairs to force more air downstairs, BUT this unfortunately also causes short cycling.

I REALLY want to get this fixed, it's hard to trust anyone after the last bit of money I spent didn't resolve the problem all the way.

I've received 3 recommendations

1. The 5" media filter installed by the guy I had do the work is potentially restricting airflow into the furnace too much in an already somewhat unstable system and a big part of the short cycling problem.

2. I should spend a bunch of money to rearchitect the main trunk into a long T shape to help make a more consistent amount of airflow and the ability to force more air downstairs since he believes the now 9 ducts going downstairs should provide enough airflow to not have short cycling.

3. Spend a ton of money and just essentially redo everything, obviously this is not optimal

EDIT: to be clear when I say short cycle this means hitting the high temp limit which is what causes the cycle to be short

Any advice would be great. I live in Northern NJ

Answer 1

1. There is no reason that you should have that much variation in your basement and top floor. It is either a storage area or a living space. If it is a living space then you have a huge insulation issue down there. Trying to solve that via more registers is idiotic. If your main level is heated properly a well insulated basement should need very very little heat. Any living space should have access to heat/air but the last HVAC guy sold you his stuff without fixing the problem.

2. Do not restrict the airflow. If you have to constantly close registers or are adding filters this is a huge waste of money. You are burning fuel to have a good percentage of your air hit a dead end. So this just makes no sense at all.

3. Understand that your main HVAC issue is the size of the unit. Anything you do to cripple the output will cost you money and your unit will not last as long.

Options...

1. Insulate your basement.

2a. Sell your furnace, install properly sized one.

2b. Live with what you have. Let it do its thing. Keep thermostat upstairs. Understand it will short cycle when it is warmer out.

The problem is most HVAC companies you call will know you have a problem and will solve it based on what they are best at or what makes them the most money. And unless you allow them to tear the whole thing out none will fully guarantee a marked improvement. And of them giving advice about filters or doing whatever to make your system less efficient I would never do business with them.

Answer 2

An explanation of cold air and warm air in a home is as follows. Cold air is heavy and flows down toward the lowest level while warm air is lighter and flows toward the highest level. This is a given in every house. That being said, I am guessing that the return grill on the top floor is in the ceiling. That would be great if you lived in south Florida or on the equator but it will never work where you live. ( A central grill is standard in most new patio style homes and is used to save money. You noticed I did not say CRAPPY INSTALLATION). No good contractor would design a system this way. This is what should have been done; how you accomplish it is up to you. Yon need a supply and return from every room with high and low return grills. The high returns are open for A/C, low returns are open for heating. If a central grill is installed on each floor then all doors that close to rooms must have enough free space under the door to allow enough air to escape. This would be your return for that room. (CHEAP) The furnace fan should be set to run on low speed continuously and switch to high when heat or A/C is running. My furnace fan Has been running for 18 years, except when my wife opens the windows. I live north of Pittsburgh, Pa. Try to find a good HVAC contractor who does great work and use him for all your needs. Correct duct sizing is also critical. Make sure all ducting is sized correctly. I am from the " old school" and always used a resistance of .08 on the return and .1 on the supply, not used much today due to cost. There is more that can be done. Too much to explain here.