2nd Stage Heat and 5th Wire?

[trebor1065]

I recently converted my furnace over to a 90% VS Two Stage Heat system.
I had a local contractor out to service the unit due to the blower was constantly running at full speed in the heat mode, the issue was corrected the original installer had the wire from the thermostat jumped from W-1 to W-2 on the furnace board. Now the heat is running in first stage and feels comfortable he informed me in order to get the unit set up properlly he needs to install a new two stage thermostat and run a fifth wire from the thermostat to the board.

My question is is the second stage heat and fifth wire required? What is the purpose of second stage heating?

[superd77]

you bought a 2 stage furnace for only 1st stage???

in order for it to work right you need a 2 stage stat.

[trebor1065]

No I did not but I was not certain how often or if the need arises for the second stage of the heating system? I live in PA and generally our winters are mild.

[gary_g]

My question is is the second stage heat and fifth wire required? What is the purpose of second stage heating?

Second stage heat provides the full btu output of the furnace. First stage is only a percentage of the total btu output.

[beenthere]

If the furnace was actually sized right. Without second stage. Your furnace won't be able to heat the house to thermostat set point, when it gets down to around 20° or so.

If its oversized, you might not not second stage. Meaning you paid for more furnace then you needed to.

What brand furnace is it.
For proper operation, you need the additional wire.
There are other ways though, and depending what brand, you won't like the way it will work.

[Frostie]

The second stage may be timed on, not requiring a 2 stage thermostat.

[BaldLoonie]

This brings up the old argument: do we time up 2nd stage even when not needed or do we use a 2 stage thermostat and bring on 2nd stage only when it is needed?

Jumping W1 to W2 brings on high in 10 minutes (most furnaces) even if low fire is all you need. This eliminates the benefit of 2 stage furnaces, gentle low for long periods in bitter weather. Most of us on here feel the right way is to use a good 2 stage stat and fire on high only as needed. Then when not needed, drop back to low for continued gentle comfort.

Not enough wires is a common issue. 2 ways to solve besides pulling new wires:

Vision Pro IAQ stat which needs 3 wires from wall unit to equipment interface at furnace. This also gives you the capability to run a humidifier. It less you take full advantage of the variable speed blower and have extra dehumidification capabilities in the summer. Great feature!

Add-a-wire device: combines the use of 2 wires into 1 wire at the stat and expands back out at the furnace. So a traditional 5 wire stat can be used now.

[CDNtech]

Ok, at the risk of sounding like a rookie, doesn't a 2 stage stat time when second stage comes on. Therefor whether you time it at the furnace or use a 2 stage stat comes down to the same thing?

[skippedover]

Ok, at the risk of sounding like a rookie, doesn't a 2 stage stat time when second stage comes on. Therefor whether you time it at the furnace or use a 2 stage stat comes down to the same thing?

You're right, you do sound like a rookie! A 2-stage stat responds to temperature rise or fall. If the temp is 70 and the stat feels it dropping toward 69 (old ones had to actually drop to 68 but the new ones, most of them, can sense the trend away from set point) it starts the furnace in 1st stage. Blower operates at a comparable speed/airflow. If the stat sense the temperature rising back to set point, it turns the unit off. If the stat senses that the room temp is maintaining within 1-degree of set point (if it's set for that or whatever the installer set if for, if it's adjustable) then it just stays on 1st stage. But if the temp falls below 1-degree below set point, then it cycles on the 2nd stage for as long as necessary to bring it back up to 1-degree, at which point it drop 2nd stage and keeps 1st stage going. How fast the room is cooling is generally dependent on what the OAT is. The colder outdoors, the more heat needed indoors. A 1-stage stat on the other hand, when connecte to the furnace, requires some other action on the part of the installer to get maximum output from the furnace. If nothing is done, the unit will probably just operate on either 1st stage all the time or 2nd stage all the time. Some furnaces require a jumper pin be moved, some require a jumper be installed between two tstat terminals. Whatever method is required, there is usually a time delay between first and second stage, for example 5 or 10 minutes before the system ramps up to 2nd stage. So for true, 2-stage operations, a 2-stage stat is needed and yes, if you've not using a wireless stat it requires an additional wire. Add in a 2-stage AC unit and you'll need another additional wire. Make that a 2-stage heat pump and you may need several more wires. Isn't this industry fun!!

[Focko]

skippedover, your response isn't entirely fair. We all know there is a wide variety of control systems. Thermostats are one variable and furnace control boards are another. Heat pump control boards and different zoning controls make for a whole lot more variables. I doubt that any of us know them all in depth. When in doubt, I read up on what I'm dealing with.

[CDNtech]

I stand corrected. Really sounded like a rookie eh?

[I_bend_metal]

Goodman furnaces DO NOT need a two stage stat to operate at a full two stage capacity...the "auto" setting on the board is all you need...(my 2 cents worth)

[skippedover]

Goodman furnaces DO NOT need a two stage stat to operate at a full two stage capacity...the "auto" setting on the board is all you need...(my 2 cents worth)

This is a false statement. In fact, if ou read the Goodman literature on wiring the 1-stage thermostat fully, they actually state "for true 2-stage operation, you need a 2-stage thermostat". IMO, if a person pays for a 2-stage furnace, they're entitled to get the full benefit of that operaton. Putting a furance on the "Auto" setting will cycle through 1st stage for either 5 or 10 minutes, depending on how it's set by the installer and then it will always go to 2nd stage. If a 2-stage stat is used, the customer will experience a much more comfortable heating system because the unit will only fire 1st stage as long as 1st stage does the job. When it gets too cold outdoors for 1st stage to do the job, then 2nd stage cycles on and off until the outdoor temp gets to design temp at which point 2nd stage is on constantly. Any colder and even 2nd stage won't do the job. IMO, it's cheating the customer to sell a 2-stage furnace and not at least tell them they should have a 2-stage stat. Honeywell is coming out with a new linen of wireless that will allow 2-stage (true 2-stage) heating and/or cooling without extra wires. :)

[webbheat]

That was a true statement, all GOODMAN furnaces are two stage and use a single stage stat except a variable speed that is a true two stage.

[Focko]

I stand corrected. Really sounded like a rookie eh?

Not at all. And you know it.

[beenthere]

I stand corrected. Really sounded like a rookie eh?
Yep.

[beenthere]

As skip said.
There are many ways a stat can handle when to bring on second stage.
Some stats use time.
Some use time and temp.
Some use temp only.

[Focko]

Shall we all resign and say that skip knows it all? I have nothing against skip, but to say everything's covered there, I'd say no.

My bigger complaint is that I thought this was a forum to learn and share knowledge, not one to prove another wrong when they are being civil. What do we have to gain if this is a contest? Internet fame? What are people doing here if the intent is not to learn?

[beenthere]

My bigger complaint is that I thought this was a forum to learn and share knowledge, not one to prove another wrong when they are being civil.

CDN asked a question and it was answered.

You may not like how it was answered, but it was answered.

[I_bend_metal]

Goodman furnaces DO NOT need a two stage stat to operate at a full two stage capacity...the "auto" setting on the board is all you need...(my 2 cents worth)

I will re-post this....because it was absolutely NOT a false statement...

[beenthere]

I will re-post this....because it was absolutely NOT a false statement...
I think they only have one line that can use a 2 stage stat.
The rest can't use one, there is no provision to use one.