New Construction - HVAC Dilemma

15 years ago

I am cross posting from the HVAC thread because this applies to both domains. Hopefully, that is within policy.

Hoping to go under contract next week on new construction. However, I am faced with an HVAC dilemma that I am having trouble solving on my own. The builder seems not inclined to let me talk directly to the HVAC sub (protecting his people from annoying customers - I imagine is his stance). However, if I pushed, I am sure I could have a conversation with the HVAC sub - however, I would like to do a little research on my own so that I can hold an intelligent conversation - and I don't want the building process to start off contentious.

House:

New Construction

2 Zones

3900 square feet

39 Windows

R13 and R19 insulation on walls.

R30 in second floor ceiling.

R19 in garage ceiling

Location: Cary, NC (Near Raleigh)

Included Equipment: (Cheapest Carrier they could find)

A/C Unit Carrier 24/ABB (One for each floor)

Furnace (Basement): Carrier 90% 58MCB

Furnace (Attic): Carrier 80% 58STA

I inquired about replacing the A/C units with a heat pump - apparently I am the only person who has asked to do that in this development. The price to do so is $1050.

The heat pump he would install is a Carrier 25HBS3 which is a 13 SEER HP.

I am trying to calculate my ROI on using a heat pump and can't seem to find a simple method to determine my payback period. If it is 5 years, then it is a slam dunk. If it is 10 years.. I am not so sure I would spent the extra money. Does anyone know what the payback period is for such a system?

Winter electric rates are: 9.634 cents per kWh

Gas costs are: 1.177 per therm.

I have tons of other questions as well:

Would a multi-stage furnace be better than a heat pump?

Should I do a heat pump only upstairs and remove the 80% furnace? In that scenario does the heat pump with electric strip backup perform better - specially since the downstairs would be fired by gas if emergency heat was needed?

I swear, HVAC is very confusing the more I look into it, the more questions I end up with!

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Comments (9)

mightyanvil
15 years ago
Any home building contract should provide for an HVAC design phase where alternatives are considered and the contractor gives the homeowner the information needed to make a smart decision. It sounds like you are the victim of the typical take-it-or-leave-it approach that developers and design/builders like to perpetrate on homeowners for their own benefit.

It's your house and your money; read the contract very carefully and try to negotiate an HVAC design meeting. There is nothing wrong with talking to a sub if the general contractor is present. If you know someone in the industry invite them to attend too. I wish I could say that I think that strategy will work but it's your only option since offering unwanted alternatives is likely to result in a poorly coordinated system.
booboo60
15 years ago
Just to educate myself I would go to an HVAC business; one independent of the builder and ask questions. There must be a certain "system" that is used most in your area; meaning the most efficient for your climate, type of build, etc.
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Sizing can be less of an issue when you have multiple units. Because each unit is controlled independently, provided of course the unit itself is not over sized for the area in which it serves resulting in excessive short cycling. In your case 3 ton plus 2 ton isn't necessarily equal to 5 tons of cooling... unless you drive those thermostats really low. By having two systems with total capacity of 5 tons (which, most of the time this would be oversized for a 1700 - 1800 sq ft structure) has a few advantages. 1. You have the ability to use one system only during low heat days or set the opposing unit higher. The unit set higher only runs if load conditions warrant.... meaning if it's not hot, the thermostat controlling the unit does not call... the unit can not run without a call... 2. Utility bills can be much less... because you rarely use both systems at the same time. You run the bedroom system when you sleep, the other when you're awake. If you have a home office in one the bedrooms you may need to rethink things a bit. 3. Extra capacity for when it's hot out. When it's hot you have the capacity to cool the home. (even while entertaining guests --- additional people add heat) Remember heat waves come, heat waves go... a so call 'properly sized' AC system is essentially properly sized roughly 10% of the time... especially if that system is a single speed AC system. Alot of people I come across like to sleep cool. So for that reason I doubt I would change the configuration of the space. Once you realize what you have, the choices you make are mostly budget type concerns. Essentially a set up like this runs like a 2 stage system. This kind of subject is above the pay grade of many... choose your contractor wisely. I service the Katy, Texas area.
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broconne
Original Author
15 years ago
That is a good idea twotogo. However, since this is a semi-custom home - they would have no interest in helping me because they wont be doing the work later.. although, it is worth a shot to find a nice one :-)
david_cary
15 years ago
broconne - well I can say that I am in a similar situation... Building 4,000 sq feet in Cary. I have the luxury of custom construction and still have to talk to my GC.

I will probably do dual fuel on the 1st floor and HP only on the 2nd. Dual fuel being 80% gas and heat pump. Electric strips are never the best choice - absolutely never. You will save money with the setup I am proposing but ROI is hard to figure. There are ways to do it but I don't have the answer. It really should be less than 5 years for a simple switch to HP in this climate - but perhaps greater than 5 years for the gas/hp hybrid setup.

But know that most people don't do HP around here because there is the impression that it won't warm the house enough (for a large house). Part of that is because insulation is not the best - since we have a fairly mild climate. Also - HP's are seen as less durable - which in fact they are.

I've built semi-custom before and never even thought of asking about changing the HVAC. So - I am not surprised that no one in your development has mentioned it.

I wish someone would give ROIs on different options but there are so many variables. Probably best is going greater than code on attic insulation. Next is reducing air infiltration. Next would be high efficiency HPs.

Those are my 3 choices. My windows are already pretty good and I am going to price out foam - primarily for the attic.
broconne
Original Author
15 years ago
David -
Which subdivision in Cary are you going to be building at?

We are going to contract next week at Horton's Creek.

Why are you dropping down to 80% gas on the first floor rather than 90+? Will you use that to offset the cost of a more efficient heat pump?
david_cary
15 years ago
No sense paying for 90% when it will only be used 10-15 nights a year (below freezing). That saves the money to go with the HE heat pump.

Stanton Place - small and almost done. Over by Kildaire and ten-ten. I've seen Horton's Creek - Crossroads area?
msm859
15 years ago
you should be asking a lot more questions -- like were are the registers? were are the returns? what is the SEER of the AC units? size? If heating is important there is only one way to go -- radiant -- NO comparison. also, 80% efficient -- I thought that was last century.
david_cary
15 years ago
msm - Yes we all should be living in houses heated with radiant and a 90+% furnace. But reality is these things cost serious $$$. Radiant heat is at least a $20k upgrade when you already have to have central air. Heating is not that important....

When you are pairing with a heat pump, in our climate, you are probably looking at less than $200 a year gas bill (for heat). So you might save $20 by going with a 95% furnace. So your payoff is looking at 100+years. Since only 1 furnace in a 1,000 will last that long - it really doesn't come close to making economic sense.

So msm859 - are you a building a house that has a budget or do you not understand our climate?
broconne
Original Author
15 years ago
David -
Actually, Horton's Creek is on the other side of Cary, off of 55. 10 Minutes to RTP, and about 20 to Chapel Hill via 751. If that gives you an idea of its location.

As for 80% vs 90%.. The only reason I can think of going to 90% is the possibility that gas could end up cheaper than electric at some point - was that a consideration you had when planning out your HVAC?

New Construction - HVAC Dilemma

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