80% vs 93% AFUE furnaces

[John Hines]

I think it is more comfort than absolute BTU efficiency. For most of the year, the lower BTU unit is fine.

All I know is that when the heat kicks on high, it is like kicking on the after burners in a jet, it cranks out a lot of heat. And I've not seen it happen yet other than in testing, it takes a multi degree thermometer change to kick it in.

I only have a single speed A/C. I keep the variable speed blower on all the time, it evens out the temp.

-- If I had something witty to say, this is where I'd say it.

[Rick F.]

What sort of PVC piping is needed for one of these more efficient models? Just curious..

[John Hines]

Typically 3".

-- If I had something witty to say, this is where I'd say it.

[Robert Gammon]

These are condensing furnaces, that is the exhaust needs to be routed horizontally out of doors and a limestone/marble bed provided underneath the outlet. Acidic water is produced and must be effectively dealt with.

[John Gilmer]

Well, it's your house.

But when you keep the air circulating when the compressor is off some of the condensation water ends up back into the house rather than being taken away. And, unfortunately, those 3 speed fans use a signficant amount of power.

[John Gilmer]

True.

Slight OT: my (our) first house had a thermocouple powered gas valve for the furnace. (This is still standard for gas powered water heaters.)

Were the electric to go out the furnace would still light up as normal. When the insides got hot, the fan controller would still attempt to switch on the fan but without electric the fan would not come up and the insides of the furnace would get hotter and hotter until the over temperature cutoff on the controller opened. When the insides cooled (from convection) the overtemp switch would open again and the cycle would start over.

Needless to say, they don't do it that way anymore.

But it is "nice" to have hot water when the electric is gone.