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Old 05-09-2012, 01:02 AM   #1
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Recommendation between different unites


hello everyone,

we are looking to get airconditioning in our 1300 sq ft house in the bay area, california. it doesn't get too hot here, but given our young family and visiting elders, it may not be a bad idea to invest a bit for the couple of months it gets warm.

so, anyway, i had no idea this would be so complicated. i got quotes from 3 contractors, and they all are very different in price and the components used. i wonder if it matters, given our planned usage. all of them asked us to change the furnace. here are the proposals:

a) 1-American Standard 80% Single Stage Furnace Model #AUE1B060A936
Warranty 20 Years Heat Exchanger / 10 Year Parts
1-American Standard 13 Seer / 3 Ton Air Conditioning System Model #4TTB3036
Warranty: 10 years
Doesn't specify the brand of the coil
14" Cooling Coil

b)
DAY AND NIGHT 95% FURNACE 3 TON 60,000
BTU MOD# N9MSE0601714A

DAY AND NIGHT EVAPORATOR COIL 3 TON
DAY AND NIGHT 13 SEER CONDENSER
MOD#N4A336AKC

c) Carrier Furnace 80% Single Stage 58STX070
AC Coil ADP C36A142C126
Carrier AC Condenser 24ABB336

I can get a 14 seer ac unit for $200 extra
Or go up to 95% furance for $675 more

My questions are:
a) which models are preferable? are there others I should ask to look into?
b) do i need 14 seers? I understand that is more power efficient. but by how much?
c) do i need a 95% furnace?

I'd rather spend a little bit ($1000) more at this time to get better reliability, warranty and power efficiency. Don't know if the power efficiency matters for 2 months of cooling in a year, maybe better to invest in a better furnace which is used for an additional 4 months in the winter?

help!

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Old 05-09-2012, 04:10 AM   #2
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Recommendation between different unites


I hear electric rates in cal are high compared to much of the east coast. So is your rate higher then 12 cents per KWH. If so, a 14 SEER would save you a fair amount over a 13 SEER in operating cost. Cal has some strange requirements in different areas. And a 14 SEER my allow you to not have to use a higher R value insulated duct. Your local contractors should be able to inform you of this if your area has those regs.

Any of those brands is fine to use.

How cold does your area get, and how hot?

Did it cost a lot to heat your home last year.

3 tons sounds big for only 1300 sq ft.

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Old 05-09-2012, 08:39 AM   #3
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Originally Posted by beenthere View Post
I hear electric rates in cal are high compared to much of the east coast. So is your rate higher then 12 cents per KWH. If so, a 14 SEER would save you a fair amount over a 13 SEER in operating cost. Cal has some strange requirements in different areas. And a 14 SEER my allow you to not have to use a higher R value insulated duct. Your local contractors should be able to inform you of this if your area has those regs.

Any of those brands is fine to use.

How cold does your area get, and how hot?

Did it cost a lot to heat your home last year.

3 tons sounds big for only 1300 sq ft.
Thanks for the reply. Our heating bills last winter (after a duct fix-up operation), ended up around 150/month. So, not too high, but we should be able to get it lower with some insulation in the attic...and a new furnace should help?

In terms of temperature extremes, in the winters it goes down to the mid-30s at the most in the nights, and summers peak out at the mid to upper 90s. 80s is more common in the summers though.
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Old 05-09-2012, 08:59 AM   #4
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Recommendation between different unites


When it comes to gas furnaces 80% can be parralleled into meaning that 80 cents of every dollar is being used towards your heating. 95 cents on a 95% efficient furnace utilize both latent and sensible heat by using heat exchanged in the condensing of the burnt gas produced from the single stage burning of it to also help heat your home so you get more bang for your buck, roughly 95 cents of every dollar.

A single stage (80%) does not condense the exhaust fumes so all that extra possible heat just goes out the exhaust pipe.

A 95% furnace is called a condensing furnace for the reason given above.

There are issues with condensing furnaces such as an intake and exhaust pipe needing to be run which pretty much means a few more holes in your walls and sometimes in extreme climates they act up but not in your area, I'd suspect. Some secondary heat exchangers, found only in condensing furnaces, have also been known to crack and fail and need replacement.

You can google for facts related to a condensing furnace to assist in your inquiry.

If you hardly ever use heat than I'd go minimum 14 seer 80% 410-A (refrigerant for cooling if you are doing the entire system) and be done with it. I'm much more a fan of "the less bells and whistles something has the less bells and whistles can fail."

That's just me. What you might really want to pay attention to and ask about is the blower motor used in the single stage furnace which the blower is obviously used in the a/c side of it as well so all the time. You can get an 80% furnace with an x-13 motor which would save you money, less electrical energy consumption versus your regular single stage motor.

http://www.cfmdistributors.com/pdfs/...3MotorTech.pdf

A 95% condensing furnace would come with a variable speed motor. That motor has a computer board in it, another bell or whistle and a highly expensive one. That single computer module on the back of a variable speed motor can cost more than an entire single stage furnace. It does use the least amount of energy but costly up front and again, if you don't use the system year round then what's the point? It'd take you decades to see any savings.
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Last edited by Doc Holliday; 05-09-2012 at 09:14 AM.
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Old 05-09-2012, 09:10 AM   #5
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Rather with a 95% furnace that's hardly ever used it'll take decades for those savings to add up enough to be of any benefit to the cost up front.
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Last edited by Doc Holliday; 05-09-2012 at 09:13 AM.
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Old 05-09-2012, 04:10 PM   #6
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Quote:
Originally Posted by globetrotter View Post
Thanks for the reply. Our heating bills last winter (after a duct fix-up operation), ended up around 150/month. So, not too high, but we should be able to get it lower with some insulation in the attic...and a new furnace should help?

In terms of temperature extremes, in the winters it goes down to the mid-30s at the most in the nights, and summers peak out at the mid to upper 90s. 80s is more common in the summers though.
A new 80% efficient furnace won't really save you any money on your heating bill. With the exception if the new one is sized for the homes actual heat loss, and the old one was over sized. So you'll need to move up to a 95% or better to see any savings as far as a new furnace.

Whats your electric rate?
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Old 05-09-2012, 07:49 PM   #7
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Have you considered a heat pump....conventional or geothermal? Geothermal will offer lower bills both heating and cooling, and a rebate is now available up to 30%
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Last edited by Missouri Bound; 05-09-2012 at 07:50 PM. Reason: spelling
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Old 05-10-2012, 01:16 PM   #8
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What about simpler options like portable or window air conditioners? If your central heating is already meeting your needs and you just want some light air conditioning for a few months out of the year it might be a much easier solution? Along the same lines there are also many mini-split AC systems that might be able to meet your needs. I've seen 27,000 BTU mini-splits that would cool 1,000 sq. ft. pretty easily and there in the ~$3k range. I suppose this all depends on what your going for though, central AC will definitely help resale value much more than any other option.

Last edited by Air-N-Water_EA; 05-10-2012 at 01:27 PM.
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Old 05-10-2012, 02:31 PM   #9
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Have you considered a heat pump....conventional or geothermal? Geothermal will offer lower bills both heating and cooling, and a rebate is now available up to 30%
Dont think he answered beentheres question about electric costs but I can guarantee that it's way over 12 cents a KW. A heat pump at Kalis high rates would be way higher than his gas bills are running.
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Old 05-10-2012, 02:33 PM   #10
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I think 3 tons is a little big for your size house and climate.
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Old 05-10-2012, 06:12 PM   #11
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A new 80% efficient furnace won't really save you any money on your heating bill. With the exception if the new one is sized for the homes actual heat loss, and the old one was over sized. So you'll need to move up to a 95% or better to see any savings as far as a new furnace.

Whats your electric rate?
Our rate is about $0.13 to $0.26 per Kwh in the summer, and $.09 to $0.14 in the winter, depending on the tiers. So far, we have been on the higher side in the winter, and on the lower side in the spring. Summer would be lower too, without AC...but that will change So, I expect around the higher side for summer as well.
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Old 05-10-2012, 06:15 PM   #12
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Originally Posted by Air-N-Water_EA View Post
What about simpler options like portable or window air conditioners? If your central heating is already meeting your needs and you just want some light air conditioning for a few months out of the year it might be a much easier solution? Along the same lines there are also many mini-split AC systems that might be able to meet your needs. I've seen 27,000 BTU mini-splits that would cool 1,000 sq. ft. pretty easily and there in the ~$3k range. I suppose this all depends on what your going for though, central AC will definitely help resale value much more than any other option.
It's a small house, but we have 3 different bedrooms and the living area that would need cooling. We would need 2 split ACs then? That would drive up the price? I did have a split AC unit earlier, and liked it, but the layout of the house allowed for 2 units to cool 1000 sq ft. Not sure how this would work here.
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Old 05-10-2012, 06:16 PM   #13
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I think 3 tons is a little big for your size house and climate.
Interesting you say that, someone else on the forum said so too...but all quotes I have have been for a 3 tonnes.
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Old 05-10-2012, 08:22 PM   #14
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Interesting you say that, someone else on the forum said so too...but all quotes I have have been for a 3 tonnes.
3 ton is way too big. My house is 2800 sq ft and mine is a 3 ton. And it gets 100 often here in the summer and it's been in the 10-20's in the winter. And my house is very comfortable. The problem with oversizing is that the house will cool too fast and dehumidification will not occur resulting in a cool and wet home. What size is the current unit?
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Old 05-10-2012, 09:01 PM   #15
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Missouri Bound hit the nail on the head. Heat intensity, an air molecule at let's say 72 degrees with a moisture content of let's say 60% feels stickier and hotter than a 72 degree air molecule with 20%-30% moisture content. You need the system to run for a length of time to dehumidify.

Cool, dry air is the want. Too big of a system and you won't achieve that. Or you'll be adding in a dehumidifer, more electricity usage.

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