Carrier #58UVB is their 95% AFUE furnace. I do not know of any material problems with this model. I have many of these units installed and have not experienced and reliability problems.

Condensate into the sump, why not. The condensate is slightly acidic but should not present any problems. If the thought bothers you, take a piece of 6"PVC with an end cap, drill a hole in the bottom, fill the PVC with marble chips (lime stone), run the condensate over the chips and drain into the sump. The ph should be around 7 which is neutral. You will get a slight by-product of co2 from the reaction.

A 16 year old house, how large? Your home should have R13 in the walls and minimum of R-30 possibly R-45 in the ceiling depending on building codes when your home was built. 100k-Btu sounds large to me, except if you have a mansion. I would advise a manual-J. How large is your existing furnace?

If you are changing your furnace to save a lot of $$ in energy costs, your savings will be about 16%. Is that enough to justify a $4000.00 investment?

Good luck,

"[current unit never broke down or needed repair in 16 yrs!]."

- Why are you replacing the current unit?

Let's say that your heating bill is $2000 per year and you save 16% per year with the 95% efficient furnace. That's $320, so it will take 12.5 years ($4000/$320 per year) to break even if natural gas stays the same price. If it goes up 25%, your payback is still almost 10 years. Now if your old furnace is broken, that's a different story.

Insert your actual numbers and do the math.

Good luck.

bonanza_Stu,
That is a great idea to have marble chips in line - thanks.

The house is 2500 sq ft, 2-storey colonial. House was built with R-13 and R-30 in the ceiling. Current one is 100,000 BTU unit.

Current unit is noisy; it is almost not possible to hear anything when in the basement and the blower comes on (checked and tested blower and motor - all OK) - we have play room and stuff. Also heating is uneven with the cycling.

Ok, the old furnace is too noisy! The 95% furnace will be a lot quieter as it has a sealed combustion system. 100K Btu, still sounds big to me. Have your contractor do a Manual-J to confirm the size.

is it a code requirement there that your flue piping must be a non-corrosive material? Like PVC or Stainless steel. If you are currently using your double wall B-vent for flue of your 80% furnace. You would 1st need a extra direct vent intake for your combustion air, then a separate out-take. Where I live, I wanted to install a 90+ furance, but with my existing flue already running through the roof, I decided to get another 80%. New flue installations depending on the height of your house and where it runs can cost almost more than the furnace itself espcially if you need to re-work the roof.