Our home was completely renovated in 2005, and new heating/cooling/ducting etc. was installed. For the past year we have struggled to get the HVAC contractors to return, as we suffer with it being too cold in the winter and not cool enough in the summer, primarily on the second floor (2 floor house + basement). Independtly, I have been told several problems exist, but I am not sure whether the advice is correct,

Problem 1. The attic space is not correctly vented (not enough vents). I do notice a large 20-30 degree difference between the attic and outside, and we also experienced ice damming last year. The attic appears well insulated with 14-16 inches of blown in insulation, vapour barrier, soffit on the rear addition, but the front 'older' part of the house roof does not have soffits.

Problem 2. We should have had 2 furnaces (split system), the house is about 6000 sqft (including finished basement). I think this would too late to rectify now ?

Problem 3. The cold air returns are a mix of pipe and cavities, the master bedroom cold air return does not work, but ultimately the furnace is not getting enough return supply of air. It was suggested that we add more supply vents from the basement hallway to the furnace (this would require minimum wall cutting). But I am not convinced this will work since the issue is in the master bedroom, far away from the furnance and new suggested air intakes ?

Can you tell me if you think these problems/resolutions sound plausible ?

There is about 3 degrees difference between each floor in the house, but upstairs the master bedroom at the rear of the house is noticably different 7-8 degrees from the floor below. also I expect we will have ice damming again this year, we were also told to fit heating cables to the roof edges where it occurs.

The attic has two issues Ventilation which can be corrected. And to much heat loss by the eves. Ice damming is caused by warm air melting the snow and as it runs towards the eaves it begins to freeze. With proper ventilation and insulation this can be corrected.

What I would do to install a new 2nd system is find all the air supply runs in the basement disconnect them from the current system and tye them into a new duct system and install a new furnace in the basement. Lots of work but less intrusive to the rest of the house.

If you do not have enough return air back to the furnace, How did you come to this conclusion? Lack of return air will cause poor heating and cause the air flow to diminish.
Or did they mean that you have no return ducts in the master bed area?

AS far as installing additional air returns in the basement hallway, i would have a concern with that. The ideal return duct set up is your supplying the same amount of air to the room as your taking away. In a basement area, if you begin to take back more air then delivered. Your basement goes under negitive air pressure in realation to the rest of the house. This can draw in radon gas into the basement, cause back drafting issues with furnaces, hot water heaters, dryers and the like. You can experiment with this by simply turing on your furnace blower at the thermostat, Fan On position. Open up the basement door just a crack and stand on the basement side of the door. Put your face near the door opening. Do you notice a breeze blowing you in your face, or does the door get forced closed? If that is the case you need to address return air in the first floor area. As this negitive air pressure is attempting to be made up by the door opening. This can cause real serious issues.

How big BTU'S is the furnace and AC system?

There are some large furnaces out there that can handle large homes. But unless the duct sytem design was perfect, very doubtfull that it will deliver the correct amount of air to the rooms.

A trick I used to do when I was doing this was to either turn off the air supply to the room in which the thermostat was in, this caused the unit to run longer thus suppling more air to the room that was not working right as it took longer for the thermostat to be satisfide, or relocate the thermostat to the troubled room and close down the air ducts to the rooms that were over heating or cooling. Its not the best method, as costs of operation go up, but it does solve the issue until a better method can be resolved.

Thankyou for your response.
I would think installing a 2nd system would result in a lot of wall cutting, and demolition of walls etc ? I assume the 2nd system could be located in the same furnance room ?
The original designer of the system suggested add more cold air returns to the basement, since the one in the master bedroom is blocked somewhere, also pipework was used, instead of floor joist cavities, which he said meant less volume being delivered. He suggsted adding cold air return in the basement, as he said the furnace/air con. is being starved of air. The furnace room does have some air ducts from outside in it, I was told that this is so the furnance and hot water tank will work more efficiently.
I believe the furnace is 100,000btu with a 3 ton a/c unit.
I am of the opinion that we should have the blocked air return in the master bedroom unblocked, and the attic corrected, before the next step, ie. either more air returns or another furnace. I am very reluctant to pull drywall down, unless it is a last resort.

If the furnace is a 100,000 unit with three tons of AC There is no way it will work on a home of 6,000 square feet. If that is really the size of the house. I think you need to check the measurements. Even idiots would not install a unit that small for a house that large.

I assume the furnace is in the basement of the home. If so and the basement is not finished all the ducts from the rooms must end up in the basement one way or the other. Simpy identify these ducts and disconnect them from the current system and connect them to a new properly sized duct. The old duct will need to come down as well and be re-sized for proper air flow as well.
You will be cutting some wall board and doing some demo.But is should be a small amount.
Of course if the basement is finished you will have to remove the ceiling to do the work.
You can also install a 2nd unit in a closet or attic area if you wish. That will require cutting walls and ceilings and running of ducts as well as gas pipes and electrical wires. The system can be overhead outlets, Not the best way for heat but will work as the lower floors will be heated anyway.
Do not use the basement as I said before for the cold air return. Unless you have the same amount of air being supplied back into the room. It is unsafe and in many areas against the codes.
Piping return ducts with metal is best, using stud cavities in my opinion is not a very good way of doing quality work. Althogh accepted.
If you think adding a return duct would work. Open a window in the basement pop open the furnace door for the fan and tape the safety switch on and run the system for a few hours to see if thsee is a difference. Keep the door opening partly blocked however. As the fan needs some resistance to properly operate.
If that does the trick, then add a metal duct to the return and pipe it to a floor grill or new wall outlet. Do not forget to remove the tape on the safety switch and close the window once the experiment is over.

thanks for your response.
The basement is finished, and I know for sure the a/c unit is 3 ton, the original design drawing, which I have, state 100,000 btu unit, its a keeprite. It could be a 125,000, and I was told that it has the biggest fan possible for that unit.
the house is 2,000 sq ft a floor, the basement is finished, so I included that in the 6,000sq ft, usable space.

A 3 ton AC is nominally adequate for a 2100 SF house, excluding the basement. If your home is 4000 SF excluding the basement, you are looking at a (nominal) 6 ton AC load, but that's based on my local design temperatures in New Jersey. This would require two systems since the largest available residential ac system is generally 5 tons.

In a multi-story structure, there will alway be a temperature difference between the two floors, no matter how carefully designed the duct system, since the airflow requirements reverse seasonaly. Single zone ACCA standards allow for a winter temperature variation of 4 degrees room to room and floor to floor, summer temperature variation of 6 degrees room to room and floor to floor. Having separate upstairs and downstairs systems makes more sense because not only do you have better temperature control, but the occupancies are different, (upstairs is usually sleeping quarters, downstairs living space,) so you can offset the temperatures during unoccupied periods, theoretically halving your heating/cooling requiremnets during those times.

As to the return air ducts, the main purpose of a return air duct is to de-pressurize the room, and to provide return air to the air handler/furnace. It does not really suck air into the room, and if the room is not getting adequate airflow even with the door open, fixing the return air in the cold room isn't the answer. Most likely you have a tortuous duct run, or the duct systemm was poorly designed. Adding more return air anywhere might help if the furnace is starved for air.

Your first step might be to try to balance the system at the main duct runs, assuming there are dampers installed. This is a subtractive process in which you remove air from the adequately heated rooms, to allow more air to reach the cold room, and to prevent the system from shuttuing down before the cold rooms warm up.

Really, you need to look for a good contractor, since your current one has left you high and dry. Carrier "Factory Authorized Dealers" are required to maintain high standards of training and customer satisfaction, so you might try to find one locally. Good luck.