Evaluate new A/C or entire HVAC system?

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Old 04-07-14, 10:07 AM
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Evaluate new A/C or entire HVAC system?

Hi all,
Our house is about 11 yrs old with central air and forced heat. Two different units, one for each floor. Last year I learned the one A/C unit has a leak, somewhere. Didnt want to spend money on searching for and then fixing the leak. Would rather put it towards a new unit.

I've received quotes from two places and am getting a third. The quotes cover the following scenarios:
  • single A/C unit replaced
  • Entire A/C and HVAC system replaced (one floor) at same 80% efficiency
  • Entire A/C and HVAC with energy efficient system (90%, 92%, and 95%)
  • Same as above but for both units

Ideally I'd replaced the entire system with the most efficient one. But of course they cost more.

So my question is around evaluating the energy efficient systems. I dont think there's any accurate way to determine the cost savings of the different units, other than running the different units in identical houses during the same time and weather conditions

One guy did tell me there's a really general rule of thumb, figuring like 8% of your normal bill with an 95% efficient unit.

Any guidance on how to figure the payback of putting in a more efficient system versus just replacing with an 80% system at a much lower cost?

thanks in advance!
 
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Old 04-07-14, 11:00 AM
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When you say efficiency percentages you're talking about the furnace portion. Look at your gas bill and figure what 10 or 15% would be and that will give you a general idea for the payback on the furnace portion. If you have other gas appliances (water heater, stove and dryer) you'll need to account for them in your gas bill you'll still be able to guestimate a reasonable payback. Down here in NC it's harder to justify higher efficiency units but the worse your winters the more a high efficiency unit will help. Saving 10% on a $200 a month gas bill might be a pretty long payback but saving 10% on a $500 or $800 bill is significantly more.

You did not mention the efficiency of the AC units you're considering but that's a bit harder to figure since lighting and other things in the home can use a significant portion of the electric bill especially if you have electric water heaters.
 
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Old 04-07-14, 01:15 PM
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thanks so much. makes sense. so 10% or 15% for the gas part.

to your question - now that you say that I remember they tell me the whole system has to be done together to get the efficiency. for example, they're quoting me on a 95% efficient system that has a Trane XV95 furnace (the 95%) with a Trane XL16i which is rated by both "seer" and "eer".

And I'm given a price for this combo. How can I tell what the payback period is for buying this combined unit? if that makes sense
 
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Old 04-07-14, 03:49 PM
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Depends on what you AC system is rated at. A 16 SEER condenser and furnace combo probably won't get you 16 SEER. Maybe 15-15.5 depending on how they install it. Why trane?
 
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Old 04-08-14, 01:17 PM
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Trane is just what the company installs that gave me the quote. I also got a quote from a company that installs Lennox. I have a Trane now. But really no clue on which brands are the best.

As far as efficiency, the "95% Full HVAC System" has the following:
  • Trane XV95 2 stage var speed furnace
  • Trane XL16i 14.75 seer 12 eer 3 ton 80k btu

I have a price for this (and the other combos).

No clue how I go about determining the potential cost savings.
My current system is about 80% (or less) the guy told me. So is it a matter of converting 95% from 80%?
 
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Old 04-09-14, 03:08 PM
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Don't be concerned about the mfg'ers A/C SEER numbers, other factors determine the SEER U get after the install.

The way U reduce energy consumption bills is to make everything more energy efficient & reduce the Btu/hr size of the equipment; that allows it to work more efficiently with a properly sealed & if needed insulated duct system.

Everyone has been encouraged to sell equipment using the SEER Savings Charts; well that is NOT being fair to your customers; instead TEST the Installed Btu/hr performance Results!.

The higher the SEER the more perfect all the supporting factors have to be...

Return-Air filter area sizing needs to be sized for under 300-fpm velocity through a media filter, a 1'' inch deep pleated filter on most filter sizing, will considerably lower SEER performance; Vetted PRO David R who does a lot of testing says; On some installations it can reduce a 14-SEER down to an 8-SEER operating performance.

Free Online Load-Calc
Print the instructions for the load-calc & follow them; print final results of the calculation; then click the SIZING LINK & print those results. Tell us the results; or copy an image of the results & upload it to this forum.
 
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Old 04-11-14, 07:27 AM
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Don't brand shop. Shop for the right company. Are they properly sizing your equipment? What type of manufacturer warranty are you getting? What type of labor warranty are you getting? With trane, you're paying for the name. I can install a brand you never heard of and it could last for 15 years, I could install a trane and it could last for the same 15 years. The biggest factor is WHO is doing the proper sizing, install and startup procedures. I would look into different brands. Goodman and amana have a phenomenal warranty and are much cheaper units than trane and lennox. You can put in a 95% 2 stage variable speed and a 2 stage communicating 18 SEER Goodman heat pump for a lot less than the Trane setup. Also, I highly doubt you need 80k btuh. Those usually come with 4 ton blowers so make sure its set up properly when they use a 3 ton condenser. Most houses in America wouldn't need 80k.
 
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Old 04-14-14, 02:52 PM
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Hi all,sorry I had no idea there were responses to this thread. this is really helpful. A few points of feedback...

HVAC Retired: thanks for the heads up on whats important. I just went to the load calulator and wow is that detailed. I started to fill it out but had to stop when it asked for the wall measurements. I dont have these offhand but this, to me, seems like the most accurate way of sizing I've come across to date (or the only one :-). This is how I operate so I'll put the work in to gathering the information. So...in the end, this thing will tell me how many "BTUs" will be needed to heat/cool my house based on the inputted parameters?

RDSTEAM - ok thanks. I really have no preference on brand and just pulled out two local installers who I've used in the past for service. they happen to install lennox and trane. to your questions, I have no clue how they sized my equipment. so i feel pretty dumb now that you ask :-) and need to find out. As far as warranty, the one place that listed it on the estimate has "10 yr parts, 10 yr comp" (assuming compressor) when I buy just the A/C unit. If I purchase the entire 95% HVAC system it says "lifetime H.E. 10 yr parts, 10yr comp". dont yet know what "H.E." means. "high efficiency"? LOL on the 80k BTU. It definitely says "3 ton 80k BTU" for the "full system" hvac on my 2nd floor. For the same system on the first floor it says "4 ton 100k BTU". I do have a rather large house @4,500 sf - could that be it?

Right now, I'm thinking the payback period on a highly efficient system could be in the 10 year range. the price between just an A/C and a full, highly efficient 95% full HVAC system is an extra $4,500 - $5,550. Again, I have a large house and use alot of energy to heat and cool it, so maybe the payback would be sooner.

Ok, will see if I can pull all the info together for that calculator and post back here. Need to make a decision before it gets to warm, but also dont want to rush and make a bad call.
 
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Old 04-14-14, 03:09 PM
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"Lifetime H.E." means lifetime warranty on the furnace heat exchanger. If the heat exchanger cracks (from thermal stress), it will let the exhaust gases into the house, causing carbon monoxide issues.
 
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Old 04-29-14, 09:02 AM
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ok, I confirmed a few things with the company that gave me the quote, specifically around the BTUs.

When I asked about the proper sizing of the systems in the estimate he told me he didnt do alot of measurements, but they've done alot of homes in my development and the sizing comes out to about the same. I actually believe that. They've done alot of homes (which is how I found them). and the homes are very similar - its a development built by a single builder with a few different models.

next, I asked about the BTUs since someone said 80,000 was high. He confirmed. And, specifically, 80,000 BTUs for the 2nd floor alone. And 100,000 btus for the first floor.

We have a large, 4500 SF home with 9' ceilings and alot of windows.

Does that BTU estimate sound way off?
 
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Old 04-29-14, 12:36 PM
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Yes I would say the sizing is off. That means you're using 40 btuh per sq ft. That's quite a bit. I understand it will be a bit higher than normal because of the ceilings and the windows, but why don't you try out the free slant fin calculator. That will give you a close estimate. And 7 tons of cooling is a lot also. I wouldn't come across as doubting them but I would expect a heat loss calc and a manual J calc to assure that they are sizing it properly. You don't want to spend 5 figures on new equipment if your not using it to its advertised potential. Remember that the longer your system runs and maintains a set temperature, the more efficient it is. If you only need 100,000 btu for the whole house and you put in 180,000 the system will start and stop nearly double the amount of times causing inefficiency, potential breakdowns and fluctuating temperature.
 
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Old 04-29-14, 01:18 PM
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wow ok good stuff. totally see what you're saying. ok will go through the steps of that calculator tonight and find out for sure. and great to understand the impact of oversizing. thanks!
 
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Old 04-30-14, 11:06 AM
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Ok, worked on the load calculator last night. And the numbers just dont add up, even close, to what the installer told me. I must be doing something wrong?

So below is the first floor only. The installer told me like 100,000 BTUs were needed, but I'm coming up with @ 20,000 BTUs.

any ideas???

 
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Old 04-30-14, 03:14 PM
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Load-Calc

Outside walls sf feet NOT figured correct...not enough wall & window sf area.

Length of outside wall in feet times height in feet = sf area of that side

Windows: use height in feet times width in feet = sf area of window or door; add all the windows & doors on that side of the house and add those on East & West sides together.
 
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Old 05-01-14, 08:01 AM
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Wow. Oh I figured I was doing something wrong! Ok thanks so much for clarifying that for me. No wonder!

Ok, so I re-did it and the numbers look more realistic. Still not close to the 100,000 BTUs they're recommending.

Thoughts? I did this for the first floor only, where I have one complete HVAC system.

First, a crude drawing of what the floor looks like with measurements. We have 9' ceilings.



And then the load-calc using true SF for all items.



Unless I'm still doing something wrong, why would I EVER need 100,000 BTUs??
 
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Old 05-01-14, 08:16 AM
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List direction of front door; front of house.

When U have it right click on Sizing link there...

It will probably be close to the same...

Using he heat load at -15F here in SW WI. It sizes heating above what the actual worst case scenarios have been the last 2-years for me!

It appears they were way oversizing for heating.
 
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Old 05-01-14, 10:19 AM
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You're probably not too far off with the 40k calculation. I can't make out some of the numbers and words but I would say thats a 100 times closer to the actual load than your potential contractor.
 
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Old 05-01-14, 11:55 AM
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Ok, see updated. I
1) marked out the location of the front door
2) blew up the readings a bit
3) ran the sizing report as well









I will mention that it seems like they are oversizing the system for my needs.
What else should I ask/say?
 
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Old 05-04-14, 11:21 AM
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Not bad on the calculation. Just realize that if they do install a unit that is much closer to the real heat loss and heat gain, your unit will have longer run times. Theres nothing wrong that, and its not going to cost anymore to run because the unit is smaller, but i will run much better.
 
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Old 05-06-14, 07:48 AM
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Thank you so much!!! This makes me feel so much better and such an accomplishment. Good to know that aspect about run time. Normally you'd think more run time = higher costs and greater chance of breakdown. But not true. amazing.

Well I spoke with the installer that I like and I was very impressed that he didnt sound defensive or act annoyed. I'm sure most people dont question them like this. He was very responsive and open to anything. Said he would come out and spend a few hours to take measurements and sizing. I also said he could send me the sizing of some of the other houses they did in our neighborhood since they're very similar. So waiting to hear back.

Just hope we can get this done before it gets too warm! But great tradeoff knowing I'm so aware and educated going into this.

thank you again! Will recap what happens next.
 
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Old 05-27-14, 08:46 AM
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Hi all,

First have to thank everyone again for all the help here. This is a big endeavor and couldnt have done it without you.

So I received my whole house load calculation from the company doing the install. To recap, the company quoted me the following on a 95% efficient HVAC system:

- Furnace: Trane XV95 2 stage var speed furnace
- Air Conditioner: Trane XL16i 14.75 seer 12 eer 3 ton 80k btu

It seemed like the 80k btu was way too high. So with help here I did my own rough calc online (above - thanks for the help) and came up with something different. Now looking at the installer's official, detailed load calc (summary below) it seems to be inline with my estimation.

So my question still remains: are they quoting me with an oversized system?


 
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Old 05-30-14, 05:09 PM
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Well the AC is oversized because they only come in full ton models, so anywhere over 2 tons and less than 3 would fall into the 3 ton category. As for the furnace, I have no clue why he's putting in an 80k furnace. The smallest one they make is 60k on high fire and thats more than enough and that has a 3 ton blower motor so it's more than sufficient.
 
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