Downstairs zone is oversized both cooling and heating, especially heating. This deserves an inquiry with GC/dealer and a thorough explanation.

And please stop all these new threads if you want this forum's help!

You are misinformed about your furnace for downstairs. The BTU numbers are just a range of the various sizes this particular model is available. Your dealer has quoted a100K model, way oversized. It even appears that a 3 ton would be adequate for downstairs AC. Of course this assumes load calc is accurate. And as I said, this furnace model is a single stage, non var speed model with high eff blower motor.

You have been quoted a low end AC condenser for downstairs. I wouldn't have it.

IMO

please do stick to one thread.

I'd take the gas furnace price & roll it over
to a properly sized heat pump...that same
15-17 SEER range I've recommended to
you several times.

understand the importance of correct sizing
of units & performance of better than minimal
hvac systems. re read threads as necessary.

best of luck.

Ok, so I deserve a lashing for starting a new thread. I was just afraid that those of you who replied earlier to my original question figured that you had given your advice and wouldn't come back to see my new question (except Mike). I need help and as you can tell, the hvac contractor just wants to sell me what he's proposed and although I think my GC is great, he has too much trust in this sub. Please continue to advise and I promise to keep it all here going forward.

As for the unit size - It was explained to me that the unit needs to be the Rec Ton as that takes into consideration other factors like the orientation of our house (back faces east). Is that not true? What is the difference between Net Ton and Rec Ton?

When I asked about the oversizing of the furnace, the hvac contractor replied, "This is the smallest furnace that is variable speed and will get you to 14 seer. If I was to drop to the 80,000, it would drop the seer rating of the system to a 13.2. " When I asked about the infinity 58CBA he replied, "You need a furnace that is at least 90% or more because of venting. With the 58 CVA you would get a furnace that is only 80% efficient".

I will ask him to clarify why he is stating this is a variable speed when it is a multi-speed.

I asked if there was a different coil that we could pair with a furnace that would give us the proper sizing. His reply was, "We can go with a 59TN6A080V21-20 furnace with a cnphp4821 coil and get the seer rating to 14.5 with a smaller furnace. Check this out and let me know what you think." I'm also re-thinking the need for gas heat over a heat pump after reading this article. "Just say no to furnace in high performance homes". I'm thinking that maybe a heat pump will give us what we need. Any thoughts?

Is there a great deal of difference between the Performance and Comfort series AC? Most of what I've read refers to the sound which I don't really think will be a a problem due to the location of the units. I'm looking for efficiency and and good dehumidification. I take it that the infinity is best at both of those but also quite pricey.

"Just say no to furnace for high performance homes"
http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/35195/Just-Say-No-to-Furnaces-in-High-Performance-Homes

We don't have gas now. Is there a way I can estimate how much gas we would use vs electric for heating? I believe we will qualify for a reduced rate through our local provider due to the increased insulation. If so, I believe rates are as follows:

NG - All Therms @ $ 1.00525 per therm

Electric -

(June-September)
First 800 kWh 0.12301
Over 800 kWh 0.13544

(October-May)
First 800 kWh 0.12301
Over 800 kWh 0.11802

Lex - as you know we have similar houses in similar climates.

We have a Carrier NG furnace for downstairs. It is way oversized but staged and variable speed and there is no downside from being oversized (that I can tell).

We are 4 tons downstairs with heat pump. I believe our furnace is 60k btus (90%). Out load for heat was something like 28k btus.

Do not stress about a large NG furnace. Your electric rates are 20% higher than ours with a similar NG rate. You should be using NG to heat....

Thanks David - that is very helpful. When we decided to build a house, I thought I'd just be picking out granite and the color of the hardwoods. :) I didn't expect having to research all of the hvac and insulation choices as well. I guess I'm just so unfamiliar with hvac that I'm afraid that I'll make a poor choice and as you see, our hvac contractor is of no help.

Absolutely disagree.

The furnace quoted is a 100 KBTU size single stage 95% efficient.The load calc indicates about 33 KBTU heat loss. Now I do believe that is on low side.

But really oversizing leads you to higher bills and less comfort.

The load calc for downstairs needs to be redone.

Your dealer is doing you an injustice by his quote and telling you the furnace model quoted is var speed when it isn't.

I would have dismissed this dealer myself. I suppose though you are too
deep in the process. The dealer will be long gone though after you move in and you will need to deal with his product/model/size selection for years to come.

IMO

Tigerdunes, thanks again for your input. Yes, we are in too deep to get out with this contractor now. What would you advise about the contractors recommendation to switch to 59TN6A080V21-20 furnace with a cnphp4821 coil?

Ask dealer these questions.

What is low stage and high stage BTU output on this furnace?

What thermostat does he propose? Be specific.

Why does he recommend a 3 1/2 ton AC condenser when his load calcs suggest a 3 ton size?

IMO

And also what design temperatures did dealer use on his load calc both inside thermostat setting and outside temperature both cooling and heating.

IMO

Tigerdunes, I will ask those questions just to be sure but I believe the thermostat is still the Edge - TP-PRH01-A
I have already asked why the 3.5 ton vs 3 ton and his reply was that the Rec ton is 3.13 which takes into consideration temperatures and orientation of the house. He said that the Net ton does not. He said that you should round up which is why he recommends the 3.5 ton.

lexmom

Still want the following answers.

What is low stage and high stage BTU output on this 80 K 58TN6 furnace?

Will the Edge thermostat control the staging of this nice 2 stg var speed furnace or will the timer on the control board?

And also what design temperatures did dealer use on his load calc both inside thermostat setting and outside temperature both cooling and heating.

And finally, will the 58TN6 furnace in a 60 K size have a compatible blower motor for a 3 1/2 ton condenser?

I know these questions don't make much sense to you but dealer will understand.

Post back.

IMO

double post.

This post was edited by tigerdunes on Wed, Mar 27, 13 at 16:55

Thanks Tigerdunes. I will ask.

The net tons is the total heat gain based on sensible and latent heat. Rec tons is the recommended size of the AC based on a 75% sensible heat capacity. It is basically a fudge factor built into the software. It does not have anything to do with the orientation of the house or temperatures. Those variables are already built into the net tons value.

This HVAC contractor is a Carrier Factory Authorized. dealer. I thought this designation meant something, but after reading these posts I am not so sure any more.

Thanks for the explanation Mike. I really thought that it was a fudge factor and that is why I asked him. He certainly told me though, that the net ton didn't account for factors like the orientation of the house.

I'm also wondering if this guy is new to the field and just isn't as knowledgeable. He is kind of young. I will be asking him more questions and will post when I get his reply.

I would not be very worried about adding a extra half ton to the AC for a house as big as yours. It is the other things this guy has proposed so far that has me very worried. Given what has transpired so far I am not sure I would trust the load calculation.

If this guy really is a Carrier Factory Authorized dealer (I am beginning to have doubts about this) then the agreement with Carrier is after the installation he has to resolve all issues to the customer's satisfaction. If he cannot, then the customer can request all equipment be removed and a full refund be made. I am not sure if this warranty applies to new construction. Call Carrier customer service to find out if you are covered.

You should tell the builder you are not impressed with what the HVAC contractor has proposed. I suggest a three way meeting with the builder and contractor and tell them exactly what you expect. In my opinion the performance to date has been unacceptable.

you could also call carrier & speak to a mfg/factory rep.
with a set of plans they can do your load calc,
for their customer (your hvac co) to follow.

the folks who work for the mfg know their stuff,
I've advised home owners quite a few times to
go this route when their hvac company refuses
or fudges load calcs.
as the hvac company gets equipment & tech
support from the mfg/co they will listen.
ask that the rep come to the job site.
hold off on any decisions until then.

I agree that your sizing is off, it is better than
it was..but still more than you need.
your house is different than poster in your area
in that you have foam insulated the roofline.
this changes the dynamics of the house greatly.

itrw what happens is that the hvac company will
either refuse to downsize, or say they won't warrenty
the job. when you balk at that...who wouldn't??..
then the whole two stage variable speed equipement
comes into play.
this is a very expensive install.

they'll sell you the 5 ton, but lower the speed of the
unit to 3-3.5 tons. the fudge factor is that if it gets
100 degrees for a week, and you have 50 people
over for a party...you'll have capacity to heat/cool.
because the unit has the feature of ramping up to
higher capacity.
this is cya for the maybe 10 days a year you might
have this situation. so that you don't call them on
xmas or 4th of july.
the other 355 days of the year, the unit will run
in low speed...at the size you actually needed.

you'll pay more in equipment costs than what
you've been spec'd to go from minimal efficiency
to optimal (not highest) efficiency.

these are the reasons...all the things you've
experienced firsthand, why homeowners pay
for independent load calcs, duct sizing & duct
design. then shop these calcs to different
hvac companie to do install.

best of luck.

Good post by energy...

Wonder if lex mom caught that cya mention....

IMO

Thank energy_rater_la. I never even considered calling the manufacturer. This company is a factory authorized rep. If I want an independent load calculation done, who would I call? Another authorized rep (not sure I'm trusting any of them now), a HERS consultant?

skip factory authorized rep.
this just means he can sell the equipment.

call mfg. ask who there can do the load calc.

do you have a HERS consultant?

getting someone with no dog in the fight is
your best bet for getting unbiased info.

Tigerdunes..I think she caught the cya part.
even though she starts multiple threads she is
learning fast!
(just had to poke you about that lexmom)

Glad to see you are keeping track of equipment
recommendations TD, not being familiar with the
various combinations strengths & weaknesses is
my weakness.

best of luck OP.

I guess it should be stated for OP even though it is known to everyone here. Being oversized for cooling is a problem, being oversized for heating is not nearly as bad when using a NG furnace.

Yes - significant oversize in heating (NG) can lead to short cycles and efficiency takes a small hit. But there is no humidity issue and a 90% less hit on unit longevity.

I'm not sure I catch exactly what Tiger is disagreeing with. Oversizing a NG furnace or using NG at all. Or something else.

My thoughts on staging. Everyone who can afford it (ie anyone building a custom house) in the Southeast should have staging and variable speed a/c. The upcharge to stage the furnace at that point is so small that everyone should have that too.

Now if the quote is for 100k and low stage is 50k, then that isn't a terrible match to 33k heat loss. Totally oversized for sure but IMO not enough to be a big problem.

Oversizing when better options are available is never a good idea whether in heating or cooling.

No I am a big proponent of nat gas and the leverage between nat gas and electric has all but diminished here in SC primarily because of the absurd electric rate increases that the PSC serves up on a platter to the major electric producers here in SC. And it should be noted that nuclear has a heavy footprint in SC. However in OP's case, I see nothing wrong with a HP system for upstairs system as long as it is speced and sized correctly. Certainly the upstairs will get some residual heat from nat gas furnace for downstairs system.

IMO

When you have an over sized furnace, in many cases you have undersized supply ducts, returns, and filters. An undersized supply duct is noisy. A small return and filter increases the static resistance. This may cause a premature failure of the blower. In some cases the furnace will tend to run hotter and eventually cause the heat exchanger to crack. It becomes a long term problem.

If this were my house I would install two high efficiency gas furnaces in the basement. I might invest in upgrading the AC to heat pumps as a hedge in case gas prices becomes more expensive relative to electricity. But honestly I think this unlikely to occur in the near future. The heat pump upgrade money could be put towards better insulation or a better furnace and AC equipment.

A good point by last post by Mike. If not individual room returns which are unlikely for new construction these days, I would want a minimum three returns downstairs, two returns upstairs-all strategically located for best airflow and comfort.

Can't recall since OP has 3-4 threads on same subject but she should want a pleated media air filter cabinet on each system.

I like the idea of the high eff nat gas furnace with AC for downstairs and straight HP system for upstairs. I might consider upgrading both condensers though to a higher SEER. Obviously though OP is working with a very poor dealer. One can only hope for the best.

If Mike had read all these threads, he would know this homeowner should
have good insulation qualities. Very difficult to follow to offer informed advice.

IMO

Thanks all for continuing to advise. I asked the questions posed by tigerdunes but have not heard back. I'm wondering if he's gotten so frustrated with me that he's ignoring me. Anyway, I'll contact my GC tomorrow to advise him that I haven't received answers to my questions.

And note that I've received a lashing for each thread I've started over and above the original one. :) Mike - we have upgraded all insulation (foam roof deck, R-15 in walls and R-30 in garage ceiling). Since I started so many threads and even confused myself when I went back to re-read them, some of the back story is that a 5 ton unit was originally proposed for downstairs (with heat pump although we requested NG) and 3.5 up. I questioned size and so they did a Manual J calculation but used code and standard options, didn't take into consideration squarefootage we eliminated, etc. I questioned again and got a revised calculation. So that's how we got where we are.

HVAC contractors (excuse the generalization) often don't have good customer communication skills. I firmly believe that they answer slowly in new construction because eventually the customer gets bogged down in all the other decisions that they give up. They certainly don't want to slow the build, so they just go with what has been handed them with just a few tweaks.

I tried to switch companies mid build but the quote was so much higher. I did get my rep demoted as he had zero skills at getting me what I wanted.

Obviously oversizing is never good but you have to pick your battles and heat is less of an issue. If you do dual fuel, then you gain an extra stage. So my system has 4 stages, 2 stages of HP and 2 stages of NG. So even though the high stage of my furnace is overkill - it is only used to recover from setbacks. There is truly an advantage when we come back from vacation to a 50 degree house....

So Tiger you disagree with NG upstairs? I wasn't even arguing for that - I was just saying that with her rates, she should be using NG.

An advantage of NG for heat upstairs is - without returns in each bedroom, the airflow goes under the doors. NG will use less airflow than a HP. That is a big reason why I converted our upstairs to NG. Downstairs - doors are not usually an issue in today's open plans. Sure - returns in each bedroom are ideal but it was $1000 when I was building and you have to pick your battles. Yes - with a/c it can be a problem also but a/c doesn't fight much at night when the sun goes down (in my case, never runs at high stage). But with heat, the hardest work comes at night when the bedroom doors are closed.

For David,

For Central metro SC, I don't think nat gas furnace is a big deal. Even for a relative mild winter climate, a good dealer (and I do question whether Lexmom has a good dealer) would most likely advise against installing a high eff condensing furnace in the attic. As I understand it, the upstairs zone is around 2000 sq ft and getting a properly sized furnace with a 3 ton rated blower would be problematic. Take a look at OP's load calc.

I get your point about heating and being oversized. But why be oversized downstairs? Get the furnace sized correctly. It will be better on comfort, operating costs, short cycling, and unnecessary wear and tear that could lead to however unlikely premature failure. I do not like the idea of buying an oversized two stage furnace where you will never need to use high stage. Paying for something that you don't need or will ever use flies in the face of good judgement.

What Carrier furnace would you recommend?

IMO

This post was edited by tigerdunes on Fri, Mar 29, 13 at 8:49

I have read all of Lexmom's posts and I remember her stating she paid an extra $1000 to foam the roof deck. My point was it may make more sense to spend the HVAC budget on better insulation rather than upgrading to a dual fuel system.

Mike, I wish it had just been 1,000 to do the foam. The thread about whether or not to foam was started in the building a home forum and dates back a couple of months. I know I've made it hard to follow. It was actually 6,500 to foam the roof deck but it is big. There is approximately 2600 on the first floor and an additional 560 in the room over garage. It is a 1.5 story with tons of unfinished storage behind knee walls on the second floor. The original proposal of 5 ton unit for the first floor took into account the foam roof deck so I have little doubt that 5 ton would have been recommended if we didn't foam. I hear there isn't a 4.5 ton. Anyway, we are receiving a 2500 credit from downsizing the units so I'm looking at the net cost being 4000. I'm comfortable with that so it it was a bad decision cost wise, don't tell me.ð I made that decision when I was out there on a mild day and it was chilly downstairs but quite warm upstairs. There was a very noticeable difference in temperature.
The 1,000 upgrades were from moving up from 13 to 14 seer. 13 being what the builder specified. 14 to 15 is an additional 800. That is for EACH unit. It was also an additional $1,100 to go from heat pump to gas downstairs.

I just got a call from the general manager of the hvac company. I think our GC told him that we have lost confidence in the company so his is personally taking over our account. We talked at length about what has transpired thus far. He offered to have a mechanical engineer re-do our Manual J calculation and will provide advice on different equipment options once the report is back. Stay tuned....

It was also an additional $1,100 to go from heat pump to gas downstairs.

wait a minute. the comparism isn't apples to apples.
starting at a base 13 seer ac with electric strip
to 13 seer ac with gas furnace...this is xxx cost
13 seer with elec strip to 13 seer heat pump is xxx cost.
this is the baseline.
gas furnaces cost more than elec strip heat in
equipment costs.
heat pump cost more than ac elec strip.

then the seer upgrades come in to play.

with the gm of the company, start with baseline
prices to get understandable, fair cost comparisms.
if you get off on the right foot...with both being
fair & open with each other, the process may
improve.

make sure that you provide information specific
to your house with house plans. while plans have
window sizes & orientation, there is a world of difference
between a double pane metal window & a double pane
low e argon filled vinyl window. things like solar heat gain coefficients & ufactors of windows should be provided.
sizes of overhangs, any exterior shading.
air infiltration in your home should be less than
normal houses if you have done your air sealing.
the foam at the roofline contributes to this air
leakage reduction. so instead of house being entered
into load calc program as average or normal, the entry
instead would be tight.
so provide information above and beyond what is spec'd
on plans and that is accurate as to what you bought & had installed.
R-values of insulation & types of insulation.

the devil is in the details...and these entries
make a load calc that is specific to what you built
instead of equal to the spec house down the street.

best of luck. (you are doing great btw)

I think I should have said 1,100 for going from electric heat strip to gas. Still not clear on heat pump vs electric heat strip although it's been explained.
I'm so glad that I've stuck with asking questions and that you all have continued to advise. While it's easier to just give up and take what they advise (and I've considered it) there is just too much money and potential future headache involved if we don't get it right. I'll post back when I hear form the GM. Probably next week, though. thanks again and have a Happy Easter!