I have a 2600+ s.q. 2 story house located in NW Indiana (built in 1979) that I have owned for 5 years. It currently has a Lennox G11E-200V-4 (200k input/160k bonnet) which I think is original, plus a Goodman 5 ton Compressor replaced in 1990 (insurance-hail damage).
I am planning on replacing the furnace this summer, as I have had nothing but problems with the free-floating blower design on this monster, as well as $ 400+ monthly utility bills in the winter.
Having relatives who own a reputable HVAC company, I have the toughest part of the install process completed (finding an installer I can trust!). After running a Manual J, one of their recommendations is a Trane XV90 (120K) furnace, along with a new coil (insurance only replaced the damaged outside unit) and a liner for the chimney. After watching this site for awhile, I just have a few questions I hope someone could help me with.
1) If I'm reading the furnace tag correctly, wouldn't my current Lennox be a 80%? Was this bad boy a top of the line unit in it's day (other than being WAY oversized)?
2) What is a reasonable expectation for the life of my Goodman 5 ton? Even though it is 15 yrs old, it never has had any problems, cools well, and is fairly inexpensive to run. I don't want to replace something for no good reason.
3) The ducts currently only have manual dampers (no zoning). Is it feasible to use the manual dampers to restrict airflow to the lower lever to increase flow upstairs (acting as manual zoning), or would that be a waste of time?
Thanks in advance for your advice
G11 furnace 68% eff. i would replace any 15 yr old unit while doing other work, especially with family in the business, yes dampers can and probably should be changed summer and winter to send more air where needed.
In the order of your questions:
(First a note) Good that you found a contractor you can trust, but what about the hired help? (just kidding.)
#1: To put the current unit in proper perspective, understand that Lennox used sequential numbers for their models. That is G7, G8, G9, etc. your G11 is probably the original unit. I would venture to say the unit was closer to 70% efficiency, than 80%. It was probably not 'top of the line' simply because there really wasn't much of a separation between 'top of the line, 'bottom of the line,' and 'middle of the line.' The 80's are really when the push began toward much higher efficiency. I am guessing that perhaps the current unit does have a automatic pilot (guessing frmo the E in the model #, maybe represents electronic ignition). Energy efficiency certainly wasn't as popular back then as it is now. With lower efficiencies (usuable heat) the input from older furnaces was usually much higher than today. In other words, an area that was serviced by this furnace will probably be serviced equally as well with a smaller unit, but the load calculations will determine that.
#2 Your best bet would be to replace the outdoor unit along with the new indoor coil so that you have a 'matched' system. Otherwise, there is no ARI (American Refrigeration Institute) rating for this outdoor unit and indoor coil combination. The national average lifespan for a system is about 13 - 15 years. Obviously that can vary depending on the service that the system receives over time. With a 15 year old condensing unit, the need to replace is probably going to be sooner than later. This would be the best and most cost-effective time to change it out.
The fact the unit is 15 years old, you're updating the remainder of the system, and ought to seriously think about updating at the same time to the new refrigerant are all valid reasons to go ahead and change it out.
#3 What will happen is that by closing too many off on the first floor, you will actually decrease the amount of air to the second floor. What will happen is that you will increase back pressure in the system since the added air has nowhere to go. It is wrong to assume this air will be 'forced' to the second floor. Keep in mind, that the duct for the second floor is sized to carry a certain amount of air and won't necessarily accomodate the added airflow. In an effort to fix one problem you will most likely create another.
If the second floor space is critical to you, make sure you have a good cold air return system in place. More often than not, this has a detrimental effect on the second floor cooling. A lot of older homes were originally designed for heating only, and cold air return from the second floor was not a priority. Look at this to see if it can be improved. The other option, that I would recommend, is to install a second cooling only system on the second floor to zone this area from the first. Sounds like a lot of added expense, but hey, you got family!
You can 'modify' the airflow throughout the entire system but you must be careful to not restrict the airflow.
If it were me..........................and I was having problems with the second floor, I would put a smaller, more cost-effective and efficient system in place for the first floor, throttle off the duct to the second floor, and install a heat pump system for the second floor. This will give you heating and cooling for the second floor with total zoning capabilities between first and second floors.
Good luck! If in doubt, check with your contractor!!!
My second floor heats and cools okay; I think it is more a matter of my wanting more constant air flow. That is why I am considering the VS, so I can keep the airflow moving; just wasn't sure if zoning would be worth the expense.
A heat pump was also suggested by my cousin, which would do double duty for me, but with Chicago's cold winters, wouldn't a heat pump become ineffective for most of the winter?
As for the A/C, the Manual J is coming up with 3 1/2 ton, while I have a 5 ton now. I'm not seeing any of the normal oversizing issues (high humidity, short cycle times,etc), so I'm a little gunshy about the 3 1/2 ton #.
I just am trying to avoid buyers remorse; with so many choices, I'm getting overloaded!
The variable speed unit reflects the trend among most systems today; and that is a more constant airflow along with even heating and cooling. Contrary to public opinion, a heat pump will still satisfy the majority of the heat requirements even at say, 30 degrees without the need for any supplemental heating. Keep in mind, that if you do zone, the first floor system will contribute to the heating of the second floor (heat rises.) I know the windy city is known for cold winters, but we have had our fair share down the road from you in the Ohio Valley. Dual fuel systems are very popular and well received here, i.e. heat pump with gas heat as second stage.
Anyway, not to confuse you any further, the manual J is the DEFINITIVE method in our industry for sizing a system. Don't be gun shy. You have a system that could have very well been oversized! There was a time, when 'bigger was (believed to be) better.' That is certainly not the case now. You will be more disappointed with an oversized system that you will be even with a properly sized system.
Personal observation: You either trust "cuz" to do the right thing or you don't. If in doubt, you can call in another contractor to provide their estimate, but I am not in favor of bringing a contractor out, if it's just to keep your cousin "honest." It's not fair to the other contractor.
If "cuz" plans to be in business for some time to come, then trust his judgement, given that it is based on industry accepted practice, and turn him loose. Keep in mind also, that if the home is zoned, i.e. one system up and one down, then either of these systems will undoubtably be smaller than the older single system.
Just because the 5 ton "worked" doesn't mean it was operating at maximum efficiency and capacity. The manual J is an extremely reliable method of sizing the system.
Remember on the J -Manual input on the slab. The perimiter insulation is important. No insulation and you are heating the concrete which is a poor insulator. If you insulate around the slab which builders seem to forget, then you will be able to put a smaller furnace in. Try the differn't insulation amounts on your j-manual and see what you can save.
I'm probably just overthinking the whole thing. I have a habit of trying to understand how everything works before I purchase, and from following this forum I felt the advice given here would be worthwhile. I already knew the old furnace was way oversized, but the terminology in A/C seemed odd to me; I have seen sites refer to the recommended furnace as a 5 ton, while the recommended a/c unit would be 3 1/2 ton. That's why I pay experts to do it right, right?!?
My cousins' are the 3rd generation running their company, and I have been around their work long enough to know I can definitely trust them (blood might be thicker than water, but it's not thick enough to fix a crappy install, right?!?)
I really appreciate the 2nd opinion you have provided; it gives me peace of mind knowing that I am on the right track.
Thanks again, and keep up the good work!