5 ton for 2570 sq ft??? and questions about upgrading seer

lexmomof3March 19, 2013

Below is an email from the hvac guy. This is for new construction, central SC, brick construction. The first floor is 2570 and upstairs is 1800 of which approximately 465 sq ft is a 13.5' x 34.5' room over the garage. The house is a 1.5 story and we're foaming the roof. A few questions:

1. HVAC guy recommends that we zone the room over the garage separately from the rest of the second floor. It is $1,000. Is that worth $1,000 and is it recommended? My husband isn't keen on the separate zone based on experience in previous house but I'm not sure exactly what his objection was. Is zoning a good way to save on energy costs?

2. He has proposed a 5 ton for the downstairs and 3 ton upstairs. Five TON seems like a lot. He is also proposing 3 TON upstairs, foam roof and about 1800 sq ft. Still seems like a lot based on what I'm familiar with (3.5 TON for 2780 sq ft poorly insulated attic with hvac in attic). Should I just trust that the tonnage is correct or is there a way to confirm. Again, new build.

Below is the increase in price for upgrading SEER levels. Any advice is greatly appreciate. Im looking for best return on investment. Also, he's quoted heatstrip for both downstairs and upstairs but we're supposed to have NG down.

FOR THE TONNAGE REDUCTION UPSTAIRS, I CAN INCLUDE A ZONE FOR THE ROOM OVER OR CHANGE ONE SYSTEM TO 14 SEER. I WOULD RECOMMEND THE ZONE DUE TO THE SIZE OF THE ROOM OVER.
Listed below are the model numbers along with the price increases from 13 seer for the downstairs 5 ton heat pump:
13 seer: OUTDOOR 25HBC360A003
INDOOR FB4CNF060T
HEATSTRIPS 10 KW
THERMOSTAT TOPTECH TT-N-851
14 seer: OUTDOOR 25HBC360A003
INDOOR FV4CNB006T
HEATSTRIPS 9 KW SMART HEAT ADD: $1,000.00
THERMIDISTAT TP-PRH-01
15 seer: OUTDOOR 25HBC560A003
INDOOR FV4CNB006T
HEATSTRIPS 9 KW SMART HEAT ADD: $1,800.00
THERMIDISTAT TP-PRH-01

15.7 seer: OUTDOOR 25HNB660C003(2-SPEED COMPRESSOR)
INDOOR FV4CNB006T
HEATSTRIPS 9KW SMART HEAT ADD: $2900.00
THERMIDISTAT TP-PRH-01
Upstairs 3 ton 13 seer split heat pump model numbers along with the price increase from 13 seer

13 seer: OUTDOOR 25HBC336A003
INDOOR FB4CNF060T
HEATSTRIPS 10 KW
THERMOSTAT TOPTECH TT-N-851
14 seer: OUTDOOR 25HBC336A003
INDOOR FV4CNB003T
HEATSTRIPS 9 KW SMART HEAT ADD: $1,000.00
THERMIDISTAT TP-PRH-01
15 seer: OUTDOOR 25HBC536A003
INDOOR FV4CNB003T
HEATSTRIPS 9 KW SMART HEAT ADD: $1,800.00
THERMIDISTAT TP-PRH-01

16 seer: OUTDOOR 25HNB636C003(2-SPEED COMPRESSOR)
INDOOR FV4CNB005T
HEATSTRIPS 9KW SMART HEAT ADD: $2900.00
THERMIDISTAT TP-PRH-01

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mike_home

Your HVAC contractor needs to perform a Manual J calculation (heating and cooling load determination) in order to arrive to the correct sizes of the heat pumps. Ask him to show you the print out of the calculation and the name of the software. If he does not do this then I suggest you find another HVAC contractor. I would not risk using rules of thumb to calculate the requirements on new construction with upgraded insulation.

The zoning of the room over the garage is probably a good idea if it is done properly. In the case of a large system the zoning becomes difficult. You want a contractor who knows how to do this.

Upgrading to 15-16 SEER is a good investment in your climate. First concentrate on getting the right size equipment. If you have high humidity in your area then I suggest in upgrading to 2-stage heat pumps.

The quote does not list a furnace so I don't understand the comment about natural gas. Do you have access to natural gas? If you do then it may make sense to get two furnaces and down grade the heat pumps to AC condensers.

    Bookmark   March 19, 2013 at 4:27PM
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lexmomof3

Mike, honestly this is over my head right now and just now getting a grasp on hvac but still don't understand all of the terminology. I thought the heatstrip part of the quote was for electric heat.

I sincerely appreciate the replies and advice as it info is starting to sink in but is still very confusing to me.

I will ask for a load calculation report.

    Bookmark   March 19, 2013 at 4:46PM
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mike_home

The terminology can get over whelming, but don't be afraid to ask questions.

The purpose of the heat strips is to provide auxiliary heat when the heat pump can't produce enough heat to satisfy the indoor temperature setting. This occurs at low temperatures (usually 30-35 degrees). If you have natural gas you could get what is called a dual fuel system. The heat strips are replaced by a gas furnace. The furnace could provide the auxiliary instead of the heat strips. The furnace is cheaper to operate than electric heat strips. If you could also just use the gas furnace for heating and not get a heat pump. In that case the outside unit (condenser) would only provide cooling in the summer.

Find out if the house will have access to natural gas. This gives you more options. In addition it can be used for cooking, drying clothes, and heating water.

    Bookmark   March 19, 2013 at 5:02PM
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ryanhughes

"I will ask for a load calculation report."

If nothing else, do this. And as said, don't accept rules of thumb or "I've been doing this X number of years." With new construction, a load calculation absolutely needs to be done. Unlike changeouts in existing homes, you now KNOW all of the building variables that affect the load.

I can tell you right now that I suspect gross oversizing for new construction, and zoning the 5 ton system is a bad idea and can be problematic, as mentioned. Zoning is great when done right. Multistage equipment is the way to go if you choose zoning, and I recommend it for comfort purposes regardless.

The heat strip is for the electric heat. Not a fan of the 25HBC outdoor units due to their lesser level of coil protection and less sound attenuating features, to say the least. They are a base grade unit. I would at least go with the Performance series outdoor units (like 25HCC6 or 25HCB7). If you're looking at Carrier equipment and zoning, Carrier's Infinity is a good system (25HNB6) but should be paired with matching Infinity indoor equipment/controller, which is not what you were quoted as an upgrade. But poorly installed, you'll hear all sorts of horror stories.

I don't know what your time frame is, but you're doing the right thing by educating yourself now. Doing HVAC right the first time will pay off enormously in comfort, efficiency, and longevity down the road.

I would personally place a large emphasis on proper duct design -- sizing/layout. See what their plans are in terms of duct material, size, insulation value, etc. Flex duct done right is okay. Flex duct, as often seen in new construction, done poorly leads to inadequate air distribution.

This post was edited by ryanhughes on Tue, Mar 19, 13 at 17:24

    Bookmark   March 19, 2013 at 5:21PM
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lexmomof3

We do have natural gas and will also be using NG for the fireplace, range and water heater.

    Bookmark   March 19, 2013 at 5:31PM
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weedmeister

It would be good to know the cost of your gas and the cost of your electricity.

You will have 3 choices. A: an all-electric system with a high efficiency HP and electric heat strips, B: a gas system with a high efficiency NG gas furnace and regular AC, and C: a hybrid system with a 80% gas furnace and a high efficiency Heat Pump.

If your gas is dirt cheap and electric is high, then B.
If your electric is cheap and gas high or so-so, A.
C might be somewhere in between.

The other factor is climate, and central SC is fairly mild winters and hot/humid summers.

If you're going to stay in this house a while, the higher SEER for AC the better.

Any vaulted ceilings? Southern exposure? Large picture windows? That all makes a difference.

    Bookmark   March 19, 2013 at 5:58PM
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energy_rater_la

your bid is for 8 tons for 2570 sq ft.
this equals out to 321 sq ft per ton.
this is grossly oversized.

the purpose of building a tight house
(ie foam insulation @ roofline & air sealing deets)
is to DOWNSIZE hvac equipment.

spending more $$ on air sealing pays off when
equipement is sized correctly.
sizing system from plans is easy.
but inputs are everything. better to have
independent do load calc & put out to bid
what is required, not just what they want
to sell you.

I've seen 2800 sq ft houses with one
5 ton system. sized & designed for needs
of the specific house, using inputs that are
exactly what was used in the house.

keep asking questions, and understand that
bigger and more equipment isn't the answer.

best of luck.

    Bookmark   March 19, 2013 at 6:57PM
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lexmomof3

Energy_rater_ la, can you further explain why you say bid is for 8 ton for 2570? I see it as 5 ton for 2570 and 3 ton for 1800. I agree that it seems oversized and i am just trying to understand so that i can ask the right questions. I have asked for the report.

    Bookmark   March 20, 2013 at 9:16AM
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energy_rater_la

my mistake, didn't realize that 5 ton was for 2570
& 3 ton for 1800 sq ft.

you do realize that rule of thumb sizing
is not the way to go?
500 sq ft per ton (and lower) is a common
rule of thumb used by companies that
don't use true entries in load calcs,
if they do load calcs at all.

the better windows, better insulation package
and air sealing results in smaller hvac, not
same sized. this is a common issue with
hvac companies.

best of luck.

    Bookmark   March 20, 2013 at 7:40PM
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fsq4cw

Just a few observations here, I would encourage you to install as energy efficient equipment as possible, 16-SEER should be a minimum. A complete Carrier Infinity system would be optimal. If possible, the location of your mechanical room should be in the center of the envelope to afford equal air distribution and maximize comfort throughout your home. Should you choose an all-electric system it is important that the backup electric elements be staged for energy efficiency as these elements are not only used for emergency heat but may be used during defrost mode as well, depending on your climate.

Regarding the size of the systems proposed, there is no mention of skylights. Skylights can have a significant impact on the size of the equipment required - particularly in air-conditioning mode!

SR

    Bookmark   March 21, 2013 at 1:01AM
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lexmomof3

Thanks fsq4cw. We are waiting on pricing for the various equipment options as well as for them to coplete the load calculation. I am hoping to do the 16 SEER.

There were skylights in the original plan but we took them out (red-line change to the plan done before bids were sent). There are no skylights and the house is framed and shingles are being put on now. We also eliminated an odd room on the first floor that accounted for approximatley 150 sq ft. My biggest concern is that since they didn't do an actual load calculation, they based the size on "rule of thumb" and didn't account for the various changes and increased insulation.

    Bookmark   March 21, 2013 at 9:15AM
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fsq4cw

While there is no substitute for a proper load calculation, systems with variable speed such as the Carrier Infinity Greenspeed (gas furnace or electric fan coil), can compensate somewhat for mistakes in load calculation if they have been up-sized. Being variable speed blower, modulating gas (furnace) and variable speed compressor, they can be set up to just throttle back to what is really required and operate just fine. True, the larger capacity will have a nominally higher up front cost but here may also be a gain in efficiency and certainly in wear and tear as these components wonâÂÂt have to operate at flat out high speed. Those things that rotate slower generally should last longer.

Regardless of what you ultimately install I would encourage you to install âÂÂWhole House Surge Protectionâ at your electrical panel entrance (loadcenter). The reason being that while we protect our computers and A/V systems with surge protecting power bars there is no other way to protect the rest of our 220-volt electrical equipment, such as our heat pumps, air-conditioners, dryers, stoves and other 110-volt equipment such as fridges etc. that all also have sensitive microprocessors. This is particularly important if you live in an area that has power outages and thunder storms, as these events will cause voltage spikes and surges that may damage this equipment and certainly shorten their serviceable life.

Look at it as insurance and a cheap investment at time of construction when balanced against the inconvenience and cost of repair or replacement.

SR

Here is a link that might be useful: Square D Whole House Surge Protection

    Bookmark   March 21, 2013 at 10:35AM
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