HP and Furnace Combination

[martlet]

Planning to replace an outside ac unit with an outside HP (copland scroll) to run to my attic - where I have a ten year old 80% still in fine operating condition. My thought is to keep the furnace so that I do not have to run another elec line to support the heat strips used for emergency heat with the HP.

Do I need any special controller board to make the combination of the new HP and the old 80% furnace to work? Will I need anything more than a good stat to make this work - ie is there any problem with a stat cutting off the HP and turning on the furnace?

As I have to replace the coil (it's bad) I know I should consider also replacing the furnace but the existing unit is performing just fine. Is there a justification in replacing an 80% 1996 furnace with an 80% 2007 furnace?

Finally - If I replace the 80% furnace with a 90% furnace - my attic is very large and will probably support a single pipe furnace. I can place the single venting pvc pipe inside of the existing metal vent to the roof with room to spare but on the roof itself I still have a metal cap. Will that metal cap need to be replaced with a non-metal cap or can I expect it to last the life of the new furnace.

Lots of questions - thanks for your assistance.

Scott

Lilburn, Georgia

[lbf]

We do a lot of jobs like these, they work great if installed properly. In my area (SW Indiana) we've found the average home can save about 600.00/yr. Our Utility rates are low at around .07/kwh and 1.45/therm. We like to use the Honeywell Pro 8000 stats and a Fossil Fuel kit. There are stats out there that do not need the FF kit but we found them difficult for the HO to use. If you install a 90+ in an attic be sure to think about how you're going to keep the condensate system from freezing.

[Airmechanical]

We do a lot of jobs like these, they work great if installed properly. We like to use the Honeywell Pro 8000 stats and a Fossil Fuel kit. .

if you would have installed and set up the 8000 properly it has a fossil fuel setting built in it!

and you should set it up properly with an outdoor sensor, that way your customer would not have to figure anything out!

except for the temperature they want their house to stay at!



.

[martlet]

Thanks IBF for the reply,

Any thoughts on the 80% furnace (comfortmaker rpjII) - I am inclined to leave this alone because it has been very reliable to this point and plan to continue to keep it maintained if kept.

Yes - I have thought about the freeze issue - my installer claimes he did the 90% in his attic and tells me there will not be a problem. I know to play it totally safe I should stay with another 80% - but why bother if my current model is doing fine.

By the way I have the rheem mod in the basement and think it deserves the praise that it gets on this site.

I will be replacing my coil with a bi-directional model to allow for a possible change later from a horizontal to a vertical furnace. If I change the furnace out in 4-5 years I know I will pay additional labor but can't think of a technical reason why this would not be a simple upgrade. Am I missing something?

Thanks for your time. I hope that after reading this site for many months I am (finally) asking a few good questions.

Scott

Lilburn, Georgia

[lbf]

if you would have installed and set up the 8000 properly it has a fossil fuel setting built in it!

and you should set it up properly with an outdoor sensor, that way your customer would not have to figure anything out!

except for the temperature they want their house to stay at!



.

Honeywell ran into patent problems when they made the Pro8000, its built in FF kit will not let you set the high and low balance points the way I like to set them. It locks out the backup heat at any temp above balance point. This means that if you set it at any thing below freezing you risk frozen pipes. If you use an external FF kit and tell the stat you are using electric back-up it will allow you to set both the high and low balance points. I set mine at 15 and 40. Martlet, Normally you can figure that a condensing type furnace will save you about 13% off your gas heating bill but with Duel Fuel the gas furnace in my area will only run about 30% of the time so you have to do some figuring to see if spending money for a new furnace is worth it.

[martlet]

Once again thanks - I have needed all of this help to encourage my (3rd!) installer that my solution is indeed possible (no one else wanted to take it on). Will continue the study on the issue of the new 80%.

Have really engoyed this website - for a consumer who is eager to learn it is the only resource of it's kind.

Cheers

Scott - Lilburn GA

"I'll send this message down the wire and hope that someone wise is listening when I go" - Dave Carter (RIP 2002)
http://members.aol.com/rongrittz/carter.htm

[ItshotinBama]

martlet, one reason for changing the furnace now is to have a complete, properly matching system. I'd suggest going with a variable speed furnace to maximize the efficiency of your new unit. A 10-yr old furnace may be working now, but what if you are faced with a $500 repair next Novemeber? Do you put another $500 into it? If not, then you just paid more for your system by splitting the install.

ibf, where are you from? Would you mind emailing me? Addy is in my profile. Thanks

[Irishmist]

You will have a dual-fuel system which will give you superb efficiency, compared to what you currently have. You may want to consider upgrading your furnace at the same time but it is certainly not a prerequisite.

Your contractor will know what to do from a control standpoint in order for your new dual fuel system to opearate properly.

If in a non-conditioned space, i.e. attic, you are going to be limited to an 80% furnace anyway unless you insulate a compartment for the 90%+ furnace since condensate will be generated during operation. Condensate + non-conditioned space = freezing water. Not a good thing.

All the best, John.

[summers]

Honeywell ran into patent problems when they made the Pro8000, its built in FF kit will not let you set the high and low balance points the way I like to set them. It locks out the backup heat at any temp above balance point. This means that if you set it at any thing below freezing you risk frozen pipes. If you use an external FF kit and tell the stat you are using electric back-up it will allow you to set both the high and low balance points. I set mine at 15 and 40. Martlet, Normally you can figure that a condensing type furnace will save you about 13% off your gas heating bill but with Duel Fuel the gas furnace in my area will only run about 30% of the time so you have to do some figuring to see if spending money for a new furnace is worth it.

Had same problem. We use now visionproIAQ and americanstandard acont402
Both allow for modulation between hp/furnace.

[martlet]

"Had same problem. We use now visionproIAQ and americanstandard acont402
Both allow for modulation between hp/furnace."

Summers,

Can you clarify...

VisionproIAQ is a Honeywelll Vision Pro IAQ Touch Screen Thermostat which accepts info from both Indoor Sensors and Outdoor Sensors ....correct?

American Standard Acont402 - hum... another Thermostat? and this is not a duplication because?

Thanks!

Scott

[summers]

"Had same problem. We use now visionproIAQ and americanstandard acont402
Both allow for modulation between hp/furnace."

Summers,

Can you clarify...

VisionproIAQ is a Honeywelll Vision Pro IAQ Touch Screen Thermostat which accepts info from both Indoor Sensors and Outdoor Sensors ....correct?

American Standard Acont402 - hum... another Thermostat? and this is not a duplication because?

Thanks!

Scott

Yes, on the visionproIAQ. Unlike the 8000, if the temp drops in the house during hp mode, it will bring on the furnace to satisfy itself (2 degree drop), or at a timed interval. You can set it so once the hp has run for a specific amount of time without satisfying, it brings on the furnace. Example: I set the hp to run to 20degrees F and the furnace cuts out at 45 degrees F. Between the two settings, the IAQ will run the hp first, and if it is not satisfied, it brings on the furnace.
The acont402 is an American Standard thermostat that does the same thing with the dual fuel without all the costly bells and whistles of the IAQ (non-programmable, no humidity functions, etc.).

Clear as mud now? Hope it helped!

DJ

[martlet]

Ok - so the VisionPro alone is what I need. If I understand you correctly there is no reason to use the two devices (VisionPro IAQ and American Standard Acont402) in tandem.

Thanks again for the clarification.

Scott

[ItshotinBama]

Yes, on the visionproIAQ. Unlike the 8000, if the temp drops in the house during hp mode, it will bring on the furnace to satisfy itself (2 degree drop), or at a timed interval. You can set it so once the hp has run for a specific amount of time without satisfying, it brings on the furnace. Example: I set the hp to run to 20degrees F and the furnace cuts out at 45 degrees F. Between the two settings, the IAQ will run the hp first, and if it is not satisfied, it brings on the furnace.
The acont402 is an American Standard thermostat that does the same thing with the dual fuel without all the costly bells and whistles of the IAQ (non-programmable, no humidity functions, etc.).

Clear as mud now? Hope it helped!

DJ


Sounds to me that the HW VisionPRo 8000 is the same as the Trane TCONT803. Touchscreen, dehumidification control, programmable, can be run in restricted or unrestricted mode.

Am I right or are there still differences?

[summers]

Sounds to me that the HW VisionPRo 8000 is the same as the Trane TCONT803. Touchscreen, dehumidification control, programmable, can be run in restricted or unrestricted mode.

Am I right or are there still differences?

You are right. We use the IAQ for when you can't pull 8 wire from tstat location, since it uses only 3 wires from stat.

[martlet]

This is exactly the info I needed- this group is great - makes me want to grow up and be a real HVAC guy!

Have been discussing this option with my current installer. The question of which controlling stat to use and how to avoid runing more wire between attic and outside were two difficult points as I am choosing to change from an outside condensor to an outside HP. Now that I have these specifics, our communication should be easier.

Without this site it is so very hard to have an informed conversation with an installer - who wants a satisfied customer but also wants to minimize time and maximize profit.

Thanks to all

Scott

[tigerdunes]

Martlett

If operating cost and comfort are important, then I suggest a high eff heat pump with var spd air handler. For the HotLanta area/climate, I think dual fuel is a waste of $$$. Run the numbers on the fuel comparison calculator.

IMO

http://www.warmair.com/html/fuel_cost_comparisons.htm