HVAC replacement

11 years ago

Hello,

We bought a house in northern NJ last year. The house has a >50 year old gas furnace (100K BTU) made by GM Delco. The AC (3 ton) is a probably 15 years old - a Trane, I believe. Both worked fine last winter and summer respectively. However, our home inspector had strongly suggested that we replace the furnace just based on its age.

So, here's the first question

1. Should I just replace the furnace and wait a little longer for the AC to be replaced or go ahead and get both replaced at the same time.

I have received a few quotes from contractors as well as service units of the gas utility company, big box stores and department stores. Only one did the Manual J calculation. The rest either eyeballed the house or simply looked at the existing units.

Here's some info about the house,

Bilevel, 1750 feet, built in 1960 with generally poor insulation, I added batts to the attic to get it up to R-30. Windows are double pane with metal frames. Doors and sliders appear drafty. 2 bedrooms over the garage get colder since there is no insulation between the garage ceiling and the bed room floors. The house has 2 feet cantilevers in the front and back that are not insulated well. The lower level is about 3 to 4 degrees colder than the upper level in winter. A gas bill of $200 for November should give some idea of where things stand.

Here are the quotes

Contractor #1
Option 1 Lennox ML180070P36A 70K BTU single stage furnace 80% AFUE, Lennox 13 SEER Condenser 13ACX-036 with matching coil, Lennox digital thermostat $5,600

Option 2 Lennox SL280UH090V36A 90K BTU 2 stage, variable speed 80% AFUE furnace, Lennox 16 SEER Condenser 14ACX-036 with matching coil, Lennox digital thermostat $6,928 minus rebate of $500

Option 3 Lennox SLP98UH090V48C 90K BTU modulating, variable speed 98% AFUE furnace, Lennox 16 SEER XC14-036 with matching coil, one new chimney liner for hot water heater, Lennox touchscreen thermostat $8,850 minus rebate of $1,800

Contractor #2
Option 1 Rheem 14AJM 36K BTU16 SEER AC with 80% AFUE 2 stage, variable speed RGPE furnace 100K BTU $6,692 minus $500 rebate

Option 2 Same AC as Option 1 with a 95% AFUE 2 stage, variable speed RGRM furnace 95K BTU $7,363 minus $1,800 rebate

I also got one Trane and 2 Carrier "quotes" that provided no details other than the furnace efficiency and AC rating. These ranged from $8,000 for the low end of efficiency/SEER to about 13K.

Based on last year, we seem to use the heating much more than the cooling. The AC saw use for less than 2 months.

So here's the next question,

2. Am I better served by going for a high efficiency furnace with a standard 13 SEER AC?

And finally,

3. Are the unit sizes ranging from 70K to 100K for the furnace and 3 ton/36K BTU FOR the AC appropriate for this house?

Thank you for reading if you have come this far!! I will appreciate any help you can offer.

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Comments (4)

mike_home
11 years ago
My recommendation would be to replace the furnace and AC at the same time so you will have a matched system. A good time to do this would be in March - April. This is when manufacturer's rebates are available and contractors are not too busy.

Stay away from the big box stores, department stores, and the gas company. Ideally you want a local HVAC company where you can speak with the owner.

Do you have know the results of the Manual J calculation? This is the only way to know if you are sized correctly. You don't want oversized equipment.

The furnace sizes from each contractor are inconsistent. I would be suspect of any contractor who would do this.

I recommend a 95%+ efficiency furnace. If you have the funds a 2-stage variable speed model would be my choice. This would enable you to get an AC with a SEER rating of 15-16. You don't need any higher in NJ.

The quote needs to have all model numbers of equipment. You should qualify for the NJ warmadvantage and cooladvantage rebates.
tigerdunes
11 years ago
I would want to see a load calculation.

Not a fan of Lennox. Don't care for the ACX series of condensers.

Go 95+% efficiency on furnace. Var speed two stage with true two stage thermostat.Add a media filter cabinet at furnace. Insulation should be evaluated including ductwork's. Make certain you have adequate return which helps even out temps in bilevels.

With a furnace that age, I would suspect it is both oversized as was very typical and most likely in 55-60% efficient range. Go ahead and replace now to take advantage of energy savings.

IMO
Good Luck!
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njheat
Original Author
11 years ago
Mike_home and Tigerdunes, thank you for your responses.

Unfortunately I don't have the Manual J calculation. I believe it was done by the Lennox dealer since he was the only one that actually measured the rooms etc and put that in his laptop. Per the Lennox quote, I need a 70K BTU for a single stage furnace but 90K BTU for a 2 stage. Does that make sense?

About air returns, the house seems to only have 1 in the upper level. The lower level has 4 supply registers but no return. Is that a good setup? If there needs to be a return in the lower level, will that add a lot of cost?

Finally, Mike_home, I live in Morris County. Would you know any good HVAC contractors in this area?

Thanks again for all your help.
mike_home
11 years ago
If the single stage 70K BTU is the correct size, then a 90K BTU 2-stage would be oversized. This assumes they are both at 80% efficiency. He should have quoted both furnaces at either 70K or 90K BTU.

Is the furnace on the lower level? If it is them adding a return may be easy. You want a contractor who inspects the duct work for size and issues.

I don't know any contractors in Morris county, but I am confident there are many good contractors in your area. My suggestion is to go the manufacturer's web sites (Carrier, Trane, Rheem, etc,) and see who has factory authorized installers near you. I find it easier if you pick one manufacturer and get 3-4 quotes on the same equipment. This will allow you to do apples to apples comparisons. You can ask them over the phone if they will do a load calculation.