View Full Version : HVAC Recommendation... Too many decisions!
12-26-2007, 03:25 PM
I'm building a new house in Kansas City. My HVAC guy wants me to choose a system and there are so many options I'm having a hard time selecting the best ones for my situation.
First, here are some details about the house: It is a reverse 1 1/2 story... It has 2000 sq ft on the main level with 2 bedrooms (master and guest), kitchen, dining room, 2 baths, laundry roomk, hearth room, and garage. The lower level is 1200 sq ft and has two bedrooms (one of which I'll use as an office), rec room, and bath. The staircase to the lower level is open (not behind a door) and the lower level walks out to the back yard. All windows are Andersen 200 series double pane, Low E and doors are likewise, Andersen.
My main concern is keeping the temperature balanced between the upper level and lower level. I work from home and will be using one of the downstairs bedrooms for my office. Therefore, I'll be downstairs all day working and I want it to be warm. I don't think cooling will be as big of an issue so I am primarily focusing on the heating. Coldest winters temperatures here are generally in the teens but can on rare occasions go into the single digits.
When I originally talked to the HVAC guy we were going to go with a 80% variable speed heat pump with electronic damper-controlled zoning (5 ton, 5x system). However, he called me back to say he reconsidered and thinks a 95% 2 stage variable speed and no zoning is the better way to go. Both options would be about the same price.
So, here are my questions...
1) If my main goal is to make sure I have even heat throughout the house, and I'm not as concerned with it costing a bit more in my utility bills, am I better off with the zoning or using the 2-stage variable speed fan?
2) Do I really need 95% efficiency? My system will be electric with a natural gas backup so I won't be using the gas that much. Any reason I shouldn't just go with something a bit less efficient and cheaper ... maybe 90% for instance? (I'm over on my building budget, of course, so want the best bang for my buck!)
Any recommendations out there?
Thanks in advance....
Brenda in Kansas City
12-26-2007, 03:38 PM
No matter what you decide for equipment. I wouldn't even consider going without zoning or 2 units on a 2 story house. To do anything less will be a lesson in futility and being uncomfortable as heck. Remember heat rises. As far as equipment, if you are going with heat pump, putting in 90+ efficiency heater would be a waste of money IMO. You'll obviously save on gas, but it will probably take quite a while to pay for itself. I do think variable speed is a nice feature though. It will be more comfortable when cooling and heating.
12-26-2007, 04:07 PM
If it were my house, I'd likely do 2 smaller systems instead of one large (5 ton) zoned system. Just my personal view plus it provides redundancy so you have heat/cool somewhere if one unit is down. But I wouldn't go without 2 systems or a zone system. Heating usually isn't a problem but rare to have a comfy upstairs with 1 unit and no zoning. If I did a big zoned system, equipment would definitely be multi-stage with a panel that could handle it. Or for those who aren't particular on brand, the Evolution or Infinity would be best.
We find that 80% and heat pump is cheaper heat than 95 and A/C in our area, which isn't that much diff from yours. Really little diff between 90 & 95 though as they are usually about the same machine with some tweaks to get the extra AFUE points.
12-26-2007, 05:33 PM
It seem that your aim is a good even temps in the house #1 and #2 utility costs. The Variable Speed 80% furnace with Heat Pump in Kansas City should give you that. If you want to spend the few dollars more for the 95% you will in the long run save that back. Without the plans in front of me It is hard to make an exact recommendation. My fist thought would be in a reverse 1 1/2 would be have you look at a 2 stage heat pump, (Trane XL16i) with either the 95% or the 80% variable speed two stage furnace (Trane XV 95 or Trane XV 80). I would suggest when ducting the house to be sure it is set up in a way that zone dampers could be added with ease if needed. I think you will find that the variable speed furnace will keep the temps pretty even without zoning but not always.
Good luck if you have any other questions feel free to send me an email or give the office a call.
12-26-2007, 05:35 PM
Instead of investing in the 90 furnace. I would go for a 2 stage/speed heat pump. Then you would get the best of both worlds in heating and cooling. We've found that a variable speed air handler evens out temps to a point, but usually only in a single story application. Depending on house, it might work on a 2 story.
12-26-2007, 05:53 PM
I would go with two units, it is easy to control the temps independently, you have some heat if one fails, and there may be savings on the ducting. Since electric heat is 100%efficient I am not sure ot the benefit of a high eff. backup gas heat. And, I might add, electric at 100% eff. doesn't mean less utility cost than gas at 80%. I don't think you will have any independent control of the first and second story temps without zoning or independent units. If you aren't going to be upstairs all day, or night, you can have some savings by running it at a different temp in both summer and winter.
12-26-2007, 06:18 PM
Either 2 small systems. Or a 2 stage VS zoned system.
12-26-2007, 08:52 PM
Well it's plain to see this forum hasn't helped you with any of your confusion now, has it? 10-replies, 10-deifferent opinions. So I guess it's up to you to decide. Here is what I'd recommend if you were my client:
1. Decide on a budget
2. Decide on your primary and secondary goals. (Economy of installation, economy of operation, greenhouse effect, comfort, etc.)
3. Decide on an installation company. The ideal company should do a Manual 'J' heat/cool load calculation and a Manual 'D' duct design. This ideal company will know the differences needed between designing for a heat pump vs. a fossil fuel system or a combination dual fuel system.
4. Have the ideal company explain the plusses and minuses of multiple pieces of equipment vs. zoning. A good company will be well versed in both systems. Of great concern with a zoned system is exactlly what strategy will be used for airflow relief when a small zone is calling. (If the company can't describe in detail what relief strategy they'll use, then they don't know zoning.)
5. Make your choice based on the above and I think you'll do just fine.
Again, if you were my client, and based on the needs of the home, assuming a single system can handle the whole house, I think I'd recommend either 80% or 95% gas but definitely, in either case, 2-stage unit with variable speed blower; 2-stage heat pump with Hybrid Heat (Carrier or Bryant) or dual fuel (everybody else) capability. This allows you to use the heat pump as a primary source of heat when the temperatures are more moderate but still have the punch of a gas furnace if it really gets cold. Using a 2-stage heat pump you can size it to heat to a lower temperature and still be able to control the cooling in the summer. I'd also invest in a zone control system with built-in relief strategy (Carrier Infinity System or Bryant Evolution System) for best system balance in all seasons. As an interesting aside, I think you'll find the heat pump slightly more efficient when connected to an 80% variable speed gas furnace than with a 95% variable speed unit. I think the reason the higher efficiency furnace is less efficient for the heat pump is the recuperative coil interferring with airflow or static pressure but I'm just guessing. I just know the ratings are a little less with the higher efficiency furnace. :)
12-27-2007, 10:53 AM
Thanks to everyone for your comments and suggestions. I spoke with my installer again and this is what we are thinking:
1) American Standard 13 SEER heat pump, 80% efficiency, with natural gas backup
2) Variable speed 2-stage fan
3) Installation of separate trunk at the furnace to allow for "future" addition of zoning, if needed (extra $250)
4) Humidifier... brand/type yet to be determined
As I explained before, I am not as concerned about spending a little extra on my heating bill as I am in making sure I'm confortable when I'm working downstairs all day. Since the gas furnace won't kick in until the temps are in the 20s, I am assuming (so correct me if I'm wrong!) that the extra 15% efficiency on the gas bill is not going to amount to much .. or at least would take a long time to pay back.
The installer assures me that the variable speed fan running on the "circulate" mode will give me an even temperature throughout the house so that it feels just as warm working in my lower level office as it does in the main level kitchen. But, just to be sure.... and to prevent alot of tearout later down the road... I thought it would be a good idea to split the trunk out now so I can do zoning if I want it later on. Installer says that will cost extra $250.
I think I'd rather spend the $250 preparing for zoning (if needed) than to upgrade to 95%.
Does anyone see any serious errors in this line of thought?
12-27-2007, 11:38 AM
That sounds like a good idea, but you should consider a two-stage unit. With a single-stage unit, when one zone calls, the condenser runs "full blast." With a two-stage unit, when one zone calls, the first stage capacity is used from the condensor. I'm not a pro so I'm not really sure how this is setup, but I'm guessing it's the zone panel that tells the condensor to run in first stage.
12-27-2007, 12:00 PM
Your approach is a mistake and a waste of time. It will cost you more to correct in the long run.
And you should go for a two stg HP condenser if you intend to use zoning controls rather than two separate systems.
I would want references to verify your dealer's HVAC zoning experience.
I would also want to know what zoning controls he proposes to use.
Sorry to be negative.
12-27-2007, 12:15 PM
Wow... waste of time... didn't see that coming! :eek:
Maybe I didn't correctly explain the setup. The heat would be 2-stage... it starts out at 60% whenever called and if that doesn't satisfy the heat requirement, it switches to 100%. I'm not sure if that is what you mean by 2-stage or if there is some "other" 2-stage. Can you elaborate?
Just a little more info... furnace speced is 120,000 BTU.
12-27-2007, 12:41 PM
The chance of having uniform heat/cool, high degree of comfort without two systems or an expertly designed zoned system is slim and none.
And you need a two stg heat pump condenser paired with your two stg var speed furnace.
I don't mean to sound negative-just trying to head you off from disappointment with a non zoned single system for two floors.
I would want to see the load calculations as well. 120 KBTU furnace even at 80% sounds too large for new home construction with good insulation qualities. HVAC is not the place to cut costs if this is your home for the future.
12-27-2007, 03:15 PM
They were referring to a 2 Stage Heat Pump.. Like the Trane XL 16i.. I'm not sure of the American Standard versions name but it will be similar. It has two-stages of cooling and two-stages of Heat pump heat. So your complete system will have 4 stages of heat (heat pump 1 & 2 and gas 1 & 2) in the summer you will have 2 stages of cooling. It will cost you a bit more up front but you will be rewarded in comfort in the coming years.
12-27-2007, 03:39 PM
Brenda, to elaborate a bit more, a two stage system works like this (suppose a Trane XL16i - 4 tons):
First stage: 4 tons x .80 (roughly 80% capacity) = 3.2 tons of heating and cooling
Second stage: 4 tons x 1.0 (100% capacity) = 4 tons of heating and cooling
The XL19i, although it uses R-22, has a more favorable capacity split in my opinion (again suppose a XL19i - 4 tons):
First stage: 4 tons x .50 (50% capacity, first compressor) = 2 tons of heating and cooling
Second stage: 4 tons x 1.0 (100% capacity, both compressors) = 4 tons of heating and cooling
Carrier has Infinity systems that are similar as well but with better controls.
Good luck. Hopefully the two-stage heat pump makes more sense to you now.
Check out carriers infinity system. Zone the house. 5 tons(112btus furnace)seems to me to be a little excessive with new construction. 2 stage variable equip will work well for your application. If you want uniform heating look towards hydronic.If you can't afford this system(infinity) do what your heating contractor tells you(he's professional).Remember you get what you pay for.
12-27-2007, 04:53 PM
You said your buget is tight.
How much better is your buget going to be, if your current choice cost you 40% more to heat and cool your house after its built.
The circ feature will help to even out the temp in your house. Will it be enough for you to be comfortable in your lower level office. Can't say, haven't seen the load calcs.
Your going to be running a 120,000 BTU furnace to be warm in one room during the day in the winter. In the summer, your going to be running a 5 ton air conditioner to be comfortable in one room during the day. Does that really make sense?
Kind of like driving a tractor trailer to the store to pick up a loaf of bread. Over kill.
12-27-2007, 05:11 PM
5 Tons? make sure your contractor does a MANUAL J load calc, and have them do the load calc room by room! You can then split the load into zones, you may find that most of the cooling load is upstairs and most of the heating load down stairs. For example, why put in a 5 ton when a 3 ton will work better? you will never know unless you do a proper load calc. Zoning with a dual capacity outdoor unit and a varible speed furnace can save you money on energy costs AND make you more comfortable! We reccomend to every customer to invest in the most energy efficient system they can afford at the time of purchase. Our country is headed for a real energy crisis in the near future. Five years from now, the at the current rate of fossil fuel increases, the 95% modulating furnace will make alot more sense when you consider it. Absolutly do the split trunkline, add manual dampers for now. I am a TRANE dealer, and I know that American Standard has a modulating zoning product. Avoid the 16i heat pump if you are going to install future zoning, the xl 19i will work more effciently and quieter. the 16i has trouble when a small zone load is used ( less then 40%) due to the compressor staging. A quality system will cost more, but last longer and cost less to operate. Good luck!
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