Are you saying that this is the only return in the house?

Yep, correct. It's a 1800 sq ft house and the return sits on the landing of the stairs in the middle of the house.

Where are you in the process - are you thinking of getting a new HVAC system or improving your ductwork? What issues do you have now?

HVAC people are most concerned about total filter area, and your filter seems to fit the 1 sq ft per ton guideline (maybe a little short).

It would seem that since this is the only return duct, it should be sized as a 3 ton main duct. The sizing on your main return duct is small for a 3 ton, more like a branch duct than the main duct. If you believe you are not getting the correct airflow, make sure that you don't use those super Merv-XX filters. A standard throwaway monthly fiberglass filter would give you the best airflow.

@udarrell Thanks. I've just been using fiberglass filters. Basically I have 122 sq in of return duct, need 288. I have 420 sq in of return grill and need a minimum of 576. I'm gonna have to put another return grill somewhere else.

@dovetonsils Basically I've had really high ($400/mo) electric bills for the last four months. 4 different HVAC technicians with 4 different opinions: 1) coil's leaking/bad from factory and need 10 kw heat strips installed, 2) heat pump is overcharged with no way leak and you have 10 kw installed but 5 are disconnected

@dovetonsils 3)probably a small refrigerant leak and wired heat strips without a new wire or breaker, 4) your ductwork is crap I can't tell anything about the heat pump because of it. Attaching the pic he drew of the current set up and his proposed. Basically some of my lines cross and others have been crawled over and there's no end cap so a lot of the air shoots right upstairs.

Pics probably don't help much. :) Basically I have 12 registers. 9 downstairs, 3 up. Upstairs is a finished A-frame, essentially one per room. 3 main branches downstairs, each goes to a box that goes to three more branches that go to registers. Upstairs is the same, just have one branch that goes up there for the three upstairs registers.

Obviously, I'm inclined to believe the fourth technician just not inclined to pay $8000. Thinking if I install a second return, re-work the plenum with an end cap, uncross and replace crushed lines. I should be good.

The return is undersized, so it would be good to increase it. The duct work should be fixed where needed. However I am skeptical it is going to have a significant impact on your $400 electric bill.

What is your electric rate? Did any of these techs confirm your refrigerant levels are correct? Is the air handler and duct work in the attic? Where are you located? What is the thermostat heat settings and do you use set backs?

My first thoughts are you are low on refrigerant and your emergency heat strips are energized all the time. If a tech can't confirm that then you need to find a someone who is competent.

I'm in SE Virginia. It's a package heat pump so the air handler's in the unit. The duct work is mostly in the crawl, besides the branch that goes upstairs and feeds three registers. Upstairs is a finished A-frame so the ductwork runs behind the knee wall. Electric bill runs $80-120 in the summer, but had 4 months this winter of $400 electric bills. Had the thermostat set on 62 and couldn't maintain that.

I only had 5 kw of heat strips wired up so they probably did run continuously. I don't remember all the pressures but the second tech said the high side was 450. Third tech tried to charge it. Couldn't get the low side over 80 and it was supposed to be 115. 60 outside and inside so I think that was his problem. Heat pumps was manufactured 2 years ago and installed a little over one.

"4 months this winter of $400 electric bills. Had the thermostat set on 62 and couldn't maintain that."

If you are using all that electricity in Virginia to maintain a temperature of 62 degrees then you am confident you have a either a leak an obstruction. It sounds like you are heating the house with the 5KW heat strips. In your climate the heat strips should not come on very often.

You should continue your plan of improving the return air flow and duct work. But based what you have posted for far your heat pump needs to be repaired.