I see a few potential issues here. First off, you're using single stage thermostats on two stage furnaces. Bad idea for comfort. Swap out the thermostats for 2 stage ones. There are many products out there that can achieve this without pulling wire. Once you do that, make sure the DIP switches on the furnace boards are set properly for 2 stage thermostats.

Also, you have 180,000 BTU input total. That's a lot of heat, and it is rare that that much is needed! How big is the house? Though I wouldn't call 45-60 minute runtimes short cycling, oversized equipment generally results in uncomfortable temperature swings.

I would also look at the particular thermostats you're using. What kind of temperature swings are you getting for each on/off cycle?

the house is a traditional 2 story colonial. 1800sqft on both floors (3600 total). the first floor unit also services the 1800ft finished basement. there are 16 registers on the first floor, 7 in the basement, and 11 on the 2nd floor. some of them have strong air flow, others not so much.

the temp swing at the 2nd floor thermostat is about 3deg, but its in the hallway where there are no registers. the bedrooms swing 8-9deg. The first floor doesn't swing as much.

I was going to order a Honeywell Prestige thermostat and the remote sensor to trigger off the temp in a bedroom (vs. the hallway). It is a 2 stage thermostat - but not sure how to hook up the 2nd stage with only 4 wires?

how can I find info on programming the furnace DIP switches properly? thanks...

This post was edited by skyjumper on Sat, Oct 18, 14 at 12:18

also the plenums on the furnaces are 22x21 output, and 24x10 input, if that matters. both have humidifiers. they don't have traditional media filters, though, but some kind of washable mesh screen thing that never seems to get dirty...

You need at least 6 wires if you have 2-stage heating. You can buy the EIM (equipment interface module) which have a wireless communication to the thermostat. Then you only need two wires at the thermostat (power and ground). The EIM will need the 6 wires but this could be installed near the furnace.

You will have to find the installation manual for your furnace. This should explain how to set the DIP switches for what you want to do.

First of all, check the settings on your thermostats. Honeywell thermostats are configured by cycles per hour, other brands are configured by a programmable temp swing.

Your furnaces sound way oversized. My house is about the size of one of your floors, and it does fine with a single 60K modulating furnace. Oversizing is not good for your comfort or the longevity of the system.

For new thermostats, I'd recommend either the VisionPro IAQ, the new VisionPro 8000 with Redlink, or the Prestige IAQ. All of those thermostats can be installed with an interface module that lets you use your existing wiring as Mike said. They will also let you slow down your variable speed blowers for better dehumidification.

I've included a link to the RGRM installation manual.

Here is a link that might be useful: RGRM instructions

My wife works for Honeywell and can get the THX9321R5030 Prestige 2.0 RedLink thermostat for $179. I don't think this is the same as the IAQ, although Honeywell's product lineup is confusing so I'm not sure what the difference is.

would the 9321 work?

thanks mike H, i'm looking into that EIM and looks like what I need. good tip.

btw - I didn't mention this before but because its not relevant to this thread (I don't think) but we actually have a 3rd forced air system for the finished space above the garage (additional space above and beyond the 3600sqft). its a 40kBTU trane system with separate AC compressor. the space is 4 rooms, and about 800sqft. so if you thought our system was over sized before....

>My wife works for Honeywell and can get the THX9321R5030 Prestige 2.0 RedLink thermostat for $179. I don't think this is the same as the IAQ, although Honeywell's product lineup is confusing so I'm not sure what the difference is.

That would work fine, but you would need to buy the interface modules separately. The Prestige IAQ is similar in functionality to the 2.0, but comes in a bundle with the module and supply/return duct temperature sensors.

>we actually have a 3rd forced air system for the finished space above the garage (additional space above and beyond the 3600sqft). its a 40kBTU trane system with separate AC compressor. the space is 4 rooms, and about 800sqft. so if you thought our system was over sized before....

Actually, that doesn't sound quite as bad as the 90K for each floor. Especially considering that 40K is the smallest size they make.

Of course, everything I'm saying here about sizing is just speculation, since I've never been to your house or done any calculations. However I'm starting to think it might be a better idea to forget about the 2 stage stats and just lock the furnaces on low stage.