2 HVAC systems for home - ideas?

9 years ago

Hello,
We are looking to replace our two 18 yr old Trane forced air HVAC units in our 3800 sq ft home near Cleveland, Ohio. About 2200 sq ft ground floor has a 100,000 btu furnace and 3.5 ton AC and second floor has 80,000 BTU furnace and 2.5 ton AC. We have large trees that provide great shade in summer. I added blown in insulation in attic to make it about R-35. House was built in 1996.

A heat pump intrigues me, but does it make sense in a two HVAC unit household? The upstairs HVAC is only on in the evening to heat/cool and the same in the early morning. The downstairs unit is always on when we're at home. Does it make sense to install a heat pump for the ground floor, and a traditional unit for the second floor? Does the advantages a heat pump provides vanish since the second floor is not always heated/cooled at all times?
Thanks for any advice! I'm sure I missed some critical piece of info. Please let me know if I did.
Jeff

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Comments (16)

mike_home
9 years ago
What fuel do you use with the current furnaces? If is natural gas then adding heat pumps may not save any money. Posting your electric and gas rates will help determine this.

If you use propane, then the heat pump will likely save money. The rates would confirm this.

If a heat pump is more economical to operate then it does not matter if the upstairs unit is not used that often.

I think the current sizes of your furnaces and AC condensers are too big. You should look for a contractor who will perform a load calculation.
tigerdunes
9 years ago
"I think the current sizes of your furnaces and AC condensers are too big. You should look for a contractor who will perform a load calculation."

I agree.

IMO
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Around here, that house would get 3 systems. I am not sure that is necessary or the most cost effective solution. But there are lots of options and you have to give a better idea of your priorities. It is install cost, ongoing costs, comfort etc? Is this forced air throughout? Do you have NG? The number of systems is not necessarily the first choice. FWIW - I have 2 systems in a similar house. So far it is working well but I just finished the walkout. Going to 1 system allows that system to be the best - 96% furnace with heat pump. The only problem in your setting is that the top floor is so much smaller than the second that short cycling of your a/c at night might be an issue with some systems. Even with Infinity running at low stage, that upstairs will get cold really fast and not dehumidify well. But if the design was really good, it might all work. What you would want is do dump some onto the first floor even though the Infinity technically doesn't allow that. All-in-all, you would need a really slick installer to get 1 system to work well. Most around here would put 3 basic systems in. Often a basic system costs less than the upgrade to a good zoned system (ie 2 basic systems cost less that 1 zoned system). At 3 floors, while the zone system would seem to get cheaper (vs 3 units), the complexity of design goes up significantly. Get 2 systems. A basic one for the upstairs (that might not be used all the time?), and a really good zoned system for the 1st 2 floors.
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The overhang issue is a big one. That along with orientation can mean the difference between not using a/c or using a lot of a/c (particularly in your climate) - particularly with 96/60 and low humidity. The unusual thing about that is that traditional construction/design keeps a house cool prior to a/c. I would presume they did it with mass in adobe construction. High desert is so ideal for mass and solar design. Manual Js are somewhat complicated but going line by line you can usually make sense of them. There is usually a summary page that includes the Heat gain and losses per item - somthing like 20,000 btuh from walls, 10,000 btuh from windows. There are measurements of walls, roof/floor, window sizes. You can't ensure that the calcs are correct but you can check the inputs. The dead ringer is infiltration - find that number and see how your house is described. This is the easiest fudge factor in my mind. They often use average - go and read what average is supposed to be - it is not new house average, it is overall average. The a/c load is possibly correct. Windows to the west can let in a lot of btus. Do you have a wall of windows to the west for a view?
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Take some sugar before you read this post... it will help this medicine go down. As far a voice control goes that would probably be the way to do it as rockypointdog suggests. A lot of this kind of stuff is moving faster than anyone can stay on top of it. Expensive : is a relative term, based upon what you are trying to do / trying to accomplish. There are a myriad of ways to cut costs, but you may not be able to do entirely what you want. With that said, many cases you are limited by what your structure provides you with. So just because something is deemed expensive doesn't mean you could pull it off anyway due to some limiting problem of the structure... like not enough room among other things. As an example: I would never attempt to twin furnaces together horizontally. Nor would I mismatch the furnaces. Any installation I do, I plan to maintain that equipment / repair it when it breaks. There are those in this industry who will sell you 'ANYTHING' no matter what. When problems start, the blame game begins... and /or they are long gone and can't be reached. So there is the expensive category done right that works. Then there is the 'here you go' we hope it works solution... then temperature extremes hit (hot or cold or both) and you're left to wonder what happened to your prize. Then there is the DIY and or silver bullet crowd... we're looking for a small cost gadget that will force my air conditioner and or heat to do what we want it to. I don't expect to gain any mass followers with these words... but let me remind you the truth (reality) is often stinging when you hear it. It is for your own good. You could waste hundreds of dollars chasing your tail, only to wind up damaging your HVAC system(s).
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Jeff
Original Author
9 years ago
Thanks for the replies.
Yes, we are using natural gas.
Electricity rate:$0.05690 per Kwh
Natural gas rate: $0.60190 per Ccf
Is loadcalc.net a reasonably accurate way to estimate BTU's needed?
If I don't go heat pump route, I would definitely spend the money on an efficient HVAC for ground floor, but should I just get a more basic unit for the 2nd floor?
Thanks,
Jeff
tigerdunes
9 years ago
No HP for first floor, just go high eff 2 stg 95% eff var speed furnace paired with min 15 SEER AC condenser.

For 2nd floor, 80% two stage var speed furnace paired with either 15 SEER AC or HP condenser.

I don't believe the rates you posted are all inclusive costs. Please dbl check.

You will need filter box cabinet and true two stage thermostat for each system. Best matching evap coils, too.

If reusing lineset, size should be verified to manufacturer spec for new condenser.

IMO
Jeff
Original Author
9 years ago
Looks like my total natural gas rate this past month was $0.77294 per CCF. For electricity the rate of $0.05690 per Kwh is correct + $36.00 per month distribution related charges.
My existing AC line has a hole, so I'm thinking I probably should switch out the line sets.
I am leaning toward American Standard Equipment. Opinions?
Thanks,
Jeff
tigerdunes
9 years ago
Load calc is needed for this zone. And AmStd HVAC is high quality.

IMO
Jeff
Original Author
9 years ago
I have to ammend my prior post: ground floor AC unit is 3 ton (not 3.5 ton).
Thanks,
Jeff
Jeff
Original Author
9 years ago
Got my first quote:
Ground floor: Gold ZM 95% variable speed furnace 100,000 BTU $2500
AC: Platinum XM Series 18 SEER 3 ton $3175
All furnace install quotes include: new thermostat, any needed gas line, metal work, electrical box, electrical whip, labor and taxes. 10 yr parts warranty, lifetime heat exchanger warranty and 1 year labor.
All AC install quotes include: new thermostat, new copper line set, air conditioner pad, disconnect, electrical whip, labor and taxes. Platinum XM AC series has 12 yr compressor warranty, 10 year parts warrant, 10 year coil warranty and 1 yr labor warranty.

I have various Gold and silver series AC and furnace quotes from same guy that top out in the 2800 dollar range for gold line for both AC and furnace unit for 2nd floor space.
What do you think?
Thanks,
Jeff
tigerdunes
9 years ago
The sizing on furnace is absolutely absurd and stupid. If the truth were known, you might could get away with a 60 K.

And any two stage furnace needs a true two stage thermostat that controls staging not a timer on furnace control board or a thermostat that works off software algorithm.

TD
Jeff
Original Author
9 years ago
This is just the first quote. I have another more knowledgeable (I think) company coming out this afternoon and another on Monday. I will ask them to calculate a manual load.

Is the Nest thermostat considered a true two stage thermostat? Or would a Honeywell Pro thermostat be a better choice?
Thanks,
Jeff

This post was edited by jhschlak on Fri, Jun 20, 14 at 11:45
tigerdunes
9 years ago
I would not recommend the Nest. I would recommend HW Prestige VP IAQ.with or without WIFI.

TD
Jeff
Original Author
9 years ago
I bet that thermostat doesn't come cheap!
mike_home
9 years ago
The second generation Nest thermostat is $250. I don't think the first generation could control 2-stage equipment. If you are going to spend that kind money, then buy one of the several Honeywell thermostats that are appropriate. If you want to save some money you can drop the WiFi feature. It is not necessary in my opinion.
Jeff
Original Author
9 years ago
Latest quote:
2 gold 96.7% 2 stage variable furnaces 80 and 60 btu
2 silver 16 seer AC units 2.5 ton and 3 ton
2 aprilaire media filter model 2410
2 Honeywell touchscreen tstats with wifi
Run new 8 wire tstat wire two both floors
Replace existing AC lines
Using american standard coils for AC units
Fixing some ductwork that is about to fall
$12,500
What do you think?
Jeff
tigerdunes
9 years ago
I would not have the Nest thermostat, any model, period. It appears the Nest is built more around the lifestyle of the homeowner over the operational functionality of the HVAC system.

Read thread below if you haven't already.

Where will furnaces be located?

I need to see the model numbers of the AC condensers and evap coils to give you an informed opinion.

Post back.

IMO

Here is a link that might be useful: Nest and Ecobee
Jeff
Original Author
9 years ago
Not getting nest. I posted that I'm getting honeywells.

2 HVAC systems for home - ideas?

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