I have a home HVAC system that is zoned into two zones. One zone runs the first floor and basement and the other runs the second floor. I am replacing both the furnace and the a/c. The salesman tells me that a two-speed furnace is more appropriate for zoned systems than a variable speed. Is that correct? I'm also looking at replacing both thermostats with digital programmable units. I know I need to buy a two-stage compatible thermostat, but will I run into any other problems considering this is a two-zoned system? Thanks much!
2 stage furnaces are fine with zoning but often that benefit is lost because most zone panels don't know how to handle them. We have a Zonex 4+2 panel which will bring the high fire on based on time but reduce it to low if the temp gets too warm with 1 zone calling. It's happy to run steadily on low all day if need be. But most panels will cycle the furnace off for a few minutes then back on low then high then off. That's very inefficient. I was talking to a Honeywell man last night, that's how their better panel does it. I wouldn't like that.
Some of the controls made to match a certain brand will offer better control of the staging. Carrier's Infinity probably would, not sure on the Lennox Harmony.
So ask lots of questions before deciding on what to do.
The EWC brand UZC3 zone control, and I assume other manufacturers 3 zone controls, can be set so that they will never call for 2nd stage heating or cooling if less than 50% of the zones are calling.
It is a 3 zone panel, so if you have only 2 zones, it will never call for 2nd stage if only one zone is calling.
You can also use standard 1h/1c thermostats with it.
Also, most furnaces with varriable speed blowers are also 2 stage heating.
and i think all new 2 stage furnaces have variable speed blowers
If you are not mistaken about what the salesman is telling you about two stage vs. variable speed then I would suggest calling a new company! As already stated in post by other people a 2 stage can or can not be useful depending on the controls. Also A variable speed blower is a must in any zone system I install......but the two things are different issues its not a matter of one over the other. That is why I suggest calling a new company.
If you are zoning a system that just shuts down certain zones when they are not calling then you should probably look for a blower that will maintain a pressure differential across the blower these fans are usually a DC motor in residential applications I know that RHEEM makes one it works very well with zoned systems that do not bypass air back to the return ( which is a crummy way of doing it).