[aaCharley]

I have a 60 year old 1 1/2 story 1800 sf house with basement. Location is northern Kentucky. Little insulation and original windows with storms. Heat is a 150K gas Sunbeam furnace. Air conditioning is with a 3Tn Sears unit. I've had a furnace man look at it and am told that the ducts are pretty adequate for what I've got installed. I'm a good enough engineer to know that the main ductwork is not undersized that it will restrict airflow - maybe not correct airflow. Evidently the ductwork was replaced when the A/C was installed 30 yrs ago. There are some baffels in the ducts. Both the furnace and the gas water heater vent up the chimney and I would like to keep that arrangement. I don't want a "booger" on the side of my house. There are only three ducts to the upper level and the stairway is the return. Maybe some sort of fan with extra power to the second floor when the A/C is running? I've heard many noise storys about that and need suggestions.

I've gathered from a lot of reading here that I do want to get some form of dual heat - Heat Pump and gas furnace. Makes a lot of sense to me, even though I make most of my money as a natural gas producer.

Now, as I conceptualize what I want, I think I would want a system set up in somewhat this configuration:
Air Filter
Heat Pump Heat Exchanger / Air Conditioner
Blower / Fan
Furnace with plenum to add heat.

I'd like to get something in the 80% gas range so that I don't have to put that booggr on the side of the house. I'm not too concerned about absolute best efficiency. I do want to be able to enjoy the immediate effects of calling for gas heat and getting it. What I have now is not very efficient, but it sure feels good when I want it to make heat, or cooling.

My thoughts on that configuration of the elements are that I want to have the Heat Pump working as long as the Outside Air Temp is greater than XXX. It will add heat to the stream, maybe not enough. With a downstream furnace, controlled by some exit temp reading telling the furncce to operate, I can still get very warm air from the vents. If the Outside Air Temp falls below XX, the heat Pump will not be in the game and the modulating furnace will carry the full load. The thermostat should allow the homeowner to set that XX number for the Heat Pump shutoff. Probably in the 20F range that it will not be energy efficient to operate with .07 kwh costs here in KY. But I don't want to have an "One or Other" system.

I sure would like to have a few advice comments on what I need. Perhaps what I want is not within the normal factory options. However, if it is, I'm sure the knowledgeable people here will know how to configure it.

 

[aaCharley]

Sounds like you've got several issues. It also sounds like your existing furnace is oversized but if the duct system is sized for a 3-ton AC system, I'd suspect the temperature rise on your furnace is astronomical and the unit is likely riding on the high limit when it runs. Based on those observations, I first and foremost recommend that a full load analysis be done on the home. Get a company in there that does Manual 'J' load analysis and once the appropriate sized of equipment are established, you can start on the 'wants'. You don't need to vent a 90+ furnace out the sidewall of the home. Most, if not all, have the capacity to vent through the roof.

Your options are many. gas warm air w/AC/HP attached, gas boiler w/hydro-air heating/cooling, ductless mini-splits to do the 2nd floor that's less than comfortable, etc. You've got a little knowledge but based on what you wrote, the old cliche, "a little knowlege is a dangerous thing" you're headed down that road without solid professional advice. So keep your questions on the table and get a good company in there to help you design something that will meet all your wishes and needs.

I've been down that "Dangerous Knowledge" path before on some other projects so I understand the advice. However, when I got finished with those projects I had acquired an education, though costly. In this case, I don't expect to be doing a HVAC project again so I don't want to get (or pay for) that sort of education on this project. I'll take the advice and try to keep it in mind.

I do believe that I want to go the gas warm air with HP attached. Possibly a little more conventional for the area and likely to get better service down the road it there are any problems.

With that set up you will rust out the furnace heat exchanger.
When the A/C runs in the summer, it will cause condesation in the furnace.

Thanks for pointing that out to me. However, I don't really understand why the AC coil I have now (located after the furnace, in the plenum) has not created that problem in the current setup during the summer cooling season. It does make sense that it would create that problem, except that it has not. Sure, I get condensation from the AC but it drains out and I've not found evidence of rusting from the moisture that is certainly remaining in the air. Everything in the current setup is over 35 yrs. old - that is how long I've owned the house. Maybe the new systems are so much tighter that the slightly more moist air will be more of a problem?

As to the vent through the roof - The one contractor whom I asked about a system told me that I would have to run a liner pipe of some sort inside the chimney pipe, if I did not go with the vent out the side of the house. He seemed to not want to do that as he thought it could lead to troubles on the install. Something to do with a condensation issue in the chimney related to the more efficient furnaces. I would have thought the gas water heater vent air would take care of the condensation. I guess not.

Anyway, I sure like the idea of the gas modulating furnace with the many incremental increases in output. And I've learned here the advantages of the variable speed blower that will help control the humidity in the summer. getting the right equipment speced and installed is the real puzzle.

Thanks to all of you for the many knowledgeable posts that I've found here. Any direct suggestions for applications on my project will be appreciated.

 

[aaCharley]

Mikey and beenthere,

Thank you both for the explanations.