Want some opinions

[komputerguy]

Hello, we are having a new furnace and AC unit installed right now. I'm kinda questioning the size they are putting in. They are installing a Goodman GMV95 95% efficient 90K BTU and a AMANA DSX16 SEER AC 3 ton unit. Our home is over 3500 sq feet. The OLD furnace they are taking out was 130K BTU and I'm not sure on the AC unit, but it is gone already. Any angles or ideas?

[the dangling wrangler]

Almost impossible to give you good information without knowing your house construction. You really should have talked with the contractor before any work started. Things can go south real quick like. Not good for either party.

[Some Dude]

And why doesnt anybody get here before the start?>

[komputerguy]

Sorry, just found you guys here. We are a split level house with an open kitchen/dining setup. I'll try and answer any questions you have.

[the dangling wrangler]

I for one won't try and second guess what your contractor has in mind. I will say this, the new furnace is a lot more efficent than the old one. So, in fact, it could be a lesser btu rating.

[gary_g]

Hello, we are having a new furnace and AC unit installed right now. I'm kinda questioning the size they are putting in. They are installing a Goodman GMV95 95% efficient 90K BTU and a AMANA DSX16 SEER AC 3 ton unit. Our home is over 3500 sq feet. The OLD furnace they are taking out was 130K BTU and I'm not sure on the AC unit, but it is gone already. Any angles or ideas?

A heat gain/loss calc (Manual J) would answer your sizing question.

[komputerguy]

I don't have Manual J or access to it. The contractor said this "if come winter it doesn't heat your home comfortably we will replace it with a higher btu one at that point."

[the dangling wrangler]

I don't have Manual J or access to it. The contractor said this "if come winter it doesn't heat your home comfortably we will replace it with a higher btu one at that point."

I usually don't knock a contractor, I have to this time. Why not just do it right the first time? That's a nice offer on his part but.... don't guess, get it right the first time around. Sounds like he's just guessing at the sizing. Not the preferred way to do things.


(top of the page, look for HVAC Calc)

[john_ertw]

I don't have Manual J or access to it. The contractor said this "if come winter it doesn't heat your home comfortably we will replace it with a higher btu one at that point."

I bet they will not be available if you get to this!

[heaterman]

Kinda of shutting the barn door after the horse is out but ask the contractor to do a heat loss / gain calc on the house. The fact of the matter is that most heating and cooling equipment is over sized to begin with, that's why a manual J is so benificial.

[gary_g]

I don't have Manual J or access to it. The contractor said this "if come winter it doesn't heat your home comfortably we will replace it with a higher btu one at that point."

Hopefully you have this in writing, and the labor is included.

Good luck.

[motoguy128]

Kinda of shutting the barn door after the horse is out but ask the contractor to do a heat loss / gain calc on the house. The fact of the matter is that most heating and cooling equipment is over sized to begin with, that's why a manual J is so benificial.

Hmmm... wonder if the contractor might manipulate the numbers to make sure it shows his equipment is sized correctly.


If the homes is well insulated, it possible that that furnace will be adequate. You just can't use a 5 degree setback on a cold night and expect it to recover in 1 hour. the contractor may have also factored in other heat loads inside the home like firepalces, flat screen TV's, normal occupancy.

I think you'll be suprise that the system will keep up nicely and be much, much quieter and more comfortable with nice even heat.

Like others said, it less of a difference than you think. If the old unit was 75% efficient, then it's output was actually 97.5k BTU. The new unit is 85.5 k BTU. So if the old unit was running 90% of the time in the coldest weather, the new unit will run about 100% of the time. That's considered to be perfectly sized.


So it goes 1st stage, then 2nd stage, then 2nd stage + heat strips.


I don;t know abotu that model, but some outdoor unit actually have 2 compressors to create 2 stages. They actually have ot stop one compressor then start the other unit. Others "unload" a single compressor. I think your proposed unit is of that type. There's a mechanism ot reduce it's capacity.. and subsuquently the electricity it consumes. In 2nd stage, it runs normally. So a 3 ton 2 stage unloading compressor, is a 3 ton compressor, that unloads to produce around 2.5 Tons in 1st stage. A 3 Ton units with 2 compressors have 1 compressor designed for abotu 1.5 Tons and the other for 3 Tons.


Just comming onto the market now, there are soem high end units that actually run the comrpessor at slower or faster speeds, to reduce capacity. Those units can drop all the way down to 10% capacity in some cases with almsot unlimted steps inbetween. Pretty cool stuff there.