can I force my new furnace to be less aggressive?

[troyport]

Modulating goodman, installed last spring. 80K BTU, and now I believe it could have been the 60K, based on how much it runs. Dang, tried so hard to get it right, and I think my tech did too. In the end, it was me who told him go with the 80K, because the numbers were just too close at zero degrees. And I knew not to oversize!
Anyway, I do like the fact that I can use a hefty set-back, I like the house cool at night. But, during the weekend day when we are holding at about 69 degrees, it will come on and not go immediately to low fire, it will stay up at around 70% for quite a while. The manual says it will "learn" how to heat the house the best over time, so I would think it would know, based on cycle times, that once it is at temperature it can just maintain at 50%, or at least attempt to. I have the full communicating t-stat, and it never overshoots.
This spring, he will be adding a 3-ton HP to the system, which will add the outdoor temp sensor. Will that have any affect on how the furnace acts (when it is cold enough for the furnace to run) Any thoughts?

[motoguy128]

THe heat pump should fill in the "Gap" for BTU output in warmer weather. So you'll have 30-36k BTU's on the heat pump, then it will transition to the furnace at around 40k. Actually, that makes the slightly oversized furnace almost ideal. Even better if you have a 2 stage heat pump, then it will run almost continously below about 40F, meaning there no real penalty for an slightly oversized furnace in this case.

[troyport]

the heat pump is a 2-stage! And I am looking forward to how it handles AC this summer. My old AC, 3 ton, same size as the HP, would cycle quite a bit unless it was brutal outside. And therefore I had temp swings and maybe not enough humidity removed on days when it wasn't so hot. I am looking forward to this new system.

[danielworkerbee]

The outdoor sensor will help the gas side, because it knows how many BTU's the home needs for the out door temperature.
luck dan

[Freezeking2000]

So are you going to over size the heat pump also because it is two stage. What is your heat gain and loss at design?

[dan sw fl]

2,100 Sq. Ft Colonial
NE Ohio

Heat Loss =~ 700 BTU per Hr/ 1'F below Thermostat Set Point [70'F]

Balance Point 33'F with
Goodman SSZ14 3 Ton

Page 22
http://www.goodmanmfg.com/Portals/0/pdf/SS/SS-SSZ14.pdf

[dan sw fl]

GOODMAN 18 SEER 3 Ton HEAT PUMP

49,000 BTU/HR at 0'F HEAT LOSS

Page 16
http://www.goodmanmfg.com/Portals/0/.../SS-DSZC18.pdf


THERMAL BALANCE POINT 30.6'F ___ SECOND STAGE
____________________.. 39'F ......... FIRST STAGE
____________________ __________

[troyport]

so it sounds like the HP should run almost all the time in the mid-30's on low stage, correct?

[motoguy128]

so it sounds like the HP should run almost all the time in the mid-30's on low stage, correct?

Correct. Keep in mind that solar heat gain and internal heat loads will reduce net heat loss. Net heat pump capacity depends on outdoor humidity levels which impact how often it defrosts. So from about 35-40F and below, the system will run almost continously unless your or using a lot of lights and appliances. A home entertainment center with a big flat screen can generate 3000BTU's of heat. So can a coffee maker is 3000 BTU's, refrigerator, toaster oven, 15 standard light 60W bulbs and so on.

[dan sw fl]

so it sounds like the HP should run almost all the time in the mid-30's on low stage, correct?

I couldn't tell you what stage it would Actually be in when it is in the 30's outside

> 40.0654321 'F ... 1st stage !
__ < 30.0123456 'F ... 2nd stage !

It depends on the sun, clouds, moon, winds and stars, time of day, ...
installation,
and whether you have treated your HP Well.
If you talk to it like a friend and wash it, the ole HP may just respond better.