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HVAC replacement and 2 stage units
Old 07-07-2017, 12:41 PM   #1
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HVAC replacement and 2 stage units

It has come time to replace the old system... the outside unit had the fan motor replaced 3 years ago but it is starting to not work off and on... the unit is 19 years old so I do not want to throw $600 at it and see how many more years I can get out of it...


BUT, I was reading about the 2 stage and variable stage ACs... the price difference between 1 stage and 2 stage is $1800... add an additional $1200 to go to variable... the SEER goes from 14.5 to 16 to 18 also...


Does anybody have a 2 stage or variable unit? Do you see a difference in comfort in the house?

We do have some humidity problems during the spring and fall when the AC is much larger than needed, but I do not know if it is worth the price difference...
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Old 07-07-2017, 01:22 PM   #2
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The key here is to get a good , conservative Manual J calculation from either a PE or a HERS rater. The vast majority of systems are way oversized and only run for short blasts. That means hot/cold/hot/cold and no run time to dry the air. Don't rely on sizing from an installer. They want you to have oversized for the equipment cost and to be darn sure they don't have to come back because the unit isn't keeping up.

This is particularly important if you choose to go variable. You want it sized just right so it runs nearly all the time at very low speed. Much higher efficiency that way. If it's oversized it's no better than the cheapest single stage as it will be cycling off and on constantly.

Green building advisor has a lot of discussion on this.
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Old 07-07-2017, 01:32 PM   #3
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Originally Posted by Texas Proud View Post
It has come time to replace the old system... the outside unit had the fan motor replaced 3 years ago but it is starting to not work off and on... the unit is 19 years old so I do not want to throw $600 at it and see how many more years I can get out of it...


BUT, I was reading about the 2 stage and variable stage ACs... the price difference between 1 stage and 2 stage is $1800... add an additional $1200 to go to variable... the SEER goes from 14.5 to 16 to 18 also...


Does anybody have a 2 stage or variable unit? Do you see a difference in comfort in the house?

We do have some humidity problems during the spring and fall when the AC is much larger than needed, but I do not know if it is worth the price difference...
Definitely listen to woodguy - sounds like he knows his stuff. I'm not expert, all I can say is that I DID pay up for variable speed fans and I DO think it made a big difference in terms of comfort. Also, because the fan usually runs at low speed, the system is extremely quiet.
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Old 07-07-2017, 02:00 PM   #4
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Definitely listen to woodguy - sounds like he knows his stuff. I'm not expert, all I can say is that I DID pay up for variable speed fans and I DO think it made a big difference in terms of comfort. Also, because the fan usually runs at low speed, the system is extremely quiet.
Be aware that variable speed fans and compressors cost a good bit more (double in the case of blowers) to replace if need be. I would install local surge protectors on both the indoor and outdoor units if they are used to protect the electronics of the motors (basically they use electrically commutated motors which have a bunch of electronics attached)
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Old 07-07-2017, 02:02 PM   #5
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My Dad has a variable unit and it works like a dream. This is his fourth season with it and the difference is quite obvious..both in comfort and in cost savings. The house isn't greatly insulated (and LOTS of glass), was built in 1973 and is single story. I will also add that this house is in N. Georgia where the summers can be quite hot and humid. When it comes time to replace ours, we too will go with the variable system.
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Old 07-07-2017, 02:15 PM   #6
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What I've read is that variable has more that can go wrong. So you need to offset the extra price not only with the higher efficiency on the plus side, maybe higher comfort on the plus side, but the possible reduced reliability and higher cost to repair on the minus side.
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Old 07-07-2017, 02:39 PM   #7
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If you choose a 2 stage make sure they install a 2 stage thermostat as well.

The other comments have been right on with regards to the sizing up the unite accordingly.
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Old 07-07-2017, 03:00 PM   #8
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What I've read is that variable has more that can go wrong. So you need to offset the extra price not only with the higher efficiency on the plus side, maybe higher comfort on the plus side, but the possible reduced reliability and higher cost to repair on the minus side.
One thing to check on is is their a 10 year parts warrunty if you jump thru the hoops (Lennos has one if you buy a complete system and register it)

On the other side running the system with continuous fan takes less than 100 watts and minimizes air stratification.
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Old 07-07-2017, 03:03 PM   #9
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What I've read is that variable has more that can go wrong. So you need to offset the extra price not only with the higher efficiency on the plus side, maybe higher comfort on the plus side, but the possible reduced reliability and higher cost to repair on the minus side.
+1

Very true. I just retired from a mega-corp that is one of the largest HVAC companies in the world. The two downsides of the variable speed units are (upfront) cost and complexity. Ideally, unless you live in the desert areas where the unit will run 7-8+ months a year (and a few of those at near continuous duty cycle), the payback is, quite possibly, negative. I live in NC and stayed with a single stage unit for the aforementioned reasons.


A compromise is to consider a thermostat that has in "intermittent" fan setting, where the fan will run about 30-40% of the time. This helps reduce hot (or cool) spots by moving the air even when the compressor or furnace is not running.

Last, as others have mentioned, the right size unit is critical.

Good luck.
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Old 07-07-2017, 03:04 PM   #10
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Does your area offer rebates? In our area, the amount of rebate is determined by the SEER/EER rating.
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Old 07-07-2017, 03:08 PM   #11
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Interestingly, I've had a handful of HVAC companies out to discuss replacement (I'm not the OP) and all have come highly-recommended via either Angie's list or local knowledgeable contacts. Not a single one was remotely interested in doing a Manual J calculation. Everything is original from when the house was built and they typically said "the builder would have known best and had the best calculations", even when I indicated substantial glass had been added since original construction.

A couple of the guys seemed very honest and up-front. For example, when I asked if the higher efficiency units were worth it, they said not in this part of the country unless electricity rates went way up. They also explained that the higher-efficiency units are more complex and more expensive to repair. They were pretty clear that the primary benefit I should consider was improved comfort and secondarily using less energy to be more green.

By conservative, do you mean one that slightly overestimates the cooling requirements or that underestimates? What is a normal expected AC cycle throughout summer? Three main summer months with average highs 80-85 and average lows 60-65.

I should add that I did a spreadsheet that used heating/cooling days from my utility bills and my actual energy consumption and it confirmed what the couple guys had told me. The fastest payback was on the unit with the lowest permitted efficiency and was at least 12 years. The higher-efficiency units got into the 20+ range. This was considering all rebates available at the time but not including any maintenance/repair costs on the new units -- which would have made the more complex units even less financially attractive. This was also without any negotiation on price. I have to think the higher-efficiency units come with a higher profit margin.

The timelines were a little shorter on the furnace side, but at the time natural gas was abnormally expensive here.

Quote:
Originally Posted by woodguy00 View Post
The key here is to get a good , conservative Manual J calculation from either a PE or a HERS rater. The vast majority of systems are way oversized and only run for short blasts. That means hot/cold/hot/cold and no run time to dry the air. Don't rely on sizing from an installer. They want you to have oversized for the equipment cost and to be darn sure they don't have to come back because the unit isn't keeping up.

This is particularly important if you choose to go variable. You want it sized just right so it runs nearly all the time at very low speed. Much higher efficiency that way. If it's oversized it's no better than the cheapest single stage as it will be cycling off and on constantly.

Green building advisor has a lot of discussion on this.
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Old 07-07-2017, 04:03 PM   #12
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Interestingly, I've had a handful of HVAC companies out to discuss replacement (I'm not the OP) and all have come highly-recommended via either Angie's list or local knowledgeable contacts. Not a single one was remotely interested in doing a Manual J calculation............
My experience, too. I found the necessary resources on line to do my own Manual J and cross checked by looking back on utility bills to confirm consumption vs heating / cooling degree days. I put in a much smaller furnace and AC unit than recommended by the salesmen, but consistent with my Manual J calculations. Both heating and cooling worked out great, with excellent dehumidification in the summer and even heat in the winter.
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Old 07-07-2017, 04:30 PM   #13
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My experience, too. I found the necessary resources on line to do my own Manual J and cross checked by looking back on utility bills to confirm consumption vs heating / cooling degree days. I put in a much smaller furnace and AC unit than recommended by the salesmen, but consistent with my Manual J calculations. Both heating and cooling worked out great, with excellent dehumidification in the summer and even heat in the winter.
That's >exactly< what I did (though I just needed to replace the furnace). Nobody would do a Manual J calculation, they just wanted to go by a rule of thumb or the plate on the old furnace (despite the fact I'd added 50% more attic insulation and replaced my leaky single-pane, aluminum-framed windows with double-paned vinyl ones). I installed a furnace 30% smaller than what they wanted to put in, it has worked great over the last 10 years, no hint of being too small.
The difference in equipment price isn't very much, I think they either didn't want to spend the time doing the calculation (it is not hard) or they just wanted to sell me something much larger than needed to be sure there wouldn't be a call-back when the weather got cold. Yes, a too-big unit leads to poor dehumidification during AC season and more hot/cold spots year-round, but those are less tangible complaints that they can more easily bat away.
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Old 07-07-2017, 04:32 PM   #14
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Since I have heat pumps it is the cold weather that controls the size of the units (combined with the resistance back up strips) (Tx Hill Country). It turns out the systems were able to hold the temp when it got down to 8 a few times. (all be it the fans ran all the time as the outside units were running and the heat strips kicked on and off).
One issue I have with the calculations is what about the record hot and cold periods that happen every so often are the systems able to handle them?
Just like my folks oversized the hot water heat in their house near Detroit, and when it got to -20 f it held the house at the desired temps where as neighbors with the default builder systems were cold.
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Old 07-07-2017, 04:43 PM   #15
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All I know is when we got our two stage Trane system our electric and gas bill dropped dramatically. We have a two zone home and haven't replaced the upstairs unit yet.
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Old 07-07-2017, 05:19 PM   #16
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One issue I have with the calculations is what about the record hot and cold periods that happen every so often are the systems able to handle them?
Yes, if you calculate the requirements yourself you can put in any assumed max/min external temperatures you choose.

The calculator here is not the one I used for my house (I can't find that one anymore online), but it looks like it asks all the right questions. As you can see, if you put in your location, it pulls up the 99% high temp and 1% low temp information.

Here's an excerpt from the ASHRAE manual giving the 1% and 99% temperatures and humidity for various locations in the US.

It's really best not to "cheat" and put in a fudge factor "just to be sure." It will only make the house less comfortable the rest of the year, and the published high/low external temps appear to be fairly conservative anyway. Anyone doing the calcs should note that the default ASHRAE assumptions (heat to 70 deg F, cool to 75 deg F) might not suit you--in which case you might change them when doing your calculations (for example, I keep the house warmer than 70 in the winter and cooler than 75 in the summer). Still, just because >you< are happy in the winter at 55 deg, the next person looking to buy your house might not be, so it's probably best to stay close to the recommendations.
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Old 07-07-2017, 05:48 PM   #17
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Thanks for the info...

To answer a question, yes the utility has a rebate program... also a rebate from Trane... total rebate $2,240 for the variable option.... the dual stage only had $500 off from Trane....


SO, as others have mentioned... nobody will do a Manual J... talked to 5 people and got the same kind of response as someguy.... also, I am pretty sure that what I have is what I need....


Also, they said that it is not as important with a variable system as it adjusts to the conditions... IOW, if I only need 40% then all I get is 40%... I was also told that the max needed is used less than 20% of the time here... that we have a 7 to 8 month of cooling so it is not ...


So, we are going with the variable system as the cost is not much more than the dual stage system and they guy said the variable is a noticeable improvement over the dual stage and the dual stage is noticeable over the single stage...

The other advantage talked about was the zoning from upstairs and downstairs... I already put one in (which I will try and sell) on my single system and it worked great... but the guy said the variable is even better.... it can adjust the dampers to what level is needed.... my current system is either on or off....


So, on Tuesday we will be getting our new system installed...
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Old 07-07-2017, 05:48 PM   #18
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Yes, if you calculate the requirements yourself you can put in any assumed max/min external temperatures you choose.

The calculator here is not the one I used for my house (I can't find that one anymore online), but it looks like it asks all the right questions. As you can see, if you put in your location, it pulls up the 99% high temp and 1% low temp information.

Here's an excerpt from the ASHRAE manual giving the 1% and 99% temperatures and humidity for various locations in the US.

It's really best not to "cheat" and put in a fudge factor "just to be sure." It will only make the house less comfortable the rest of the year, and the published high/low external temps appear to be fairly conservative anyway. Anyone doing the calcs should note that the default ASHRAE assumptions (heat to 70 deg F, cool to 75 deg F) might not suit you--in which case you might change them when doing your calculations (for example, I keep the house warmer than 70 in the winter and cooler than 75 in the summer). Still, just because >you< are happy in the winter at 55 deg, the next person looking to buy your house might not be, so it's probably best to stay close to the recommendations.
Im commenting so I can find this link later when I need it
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Old 08-09-2017, 05:55 PM   #19
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I don't know anything about Manual J. I'm just a DIY homeowner. But I found this site to help me calculate it: coolcalc.com (free online system, uses GPS to simplify measurements; but requires signup.)
I've attached the calculated output for my 2 systems and would like help understanding what it means
FYI, my home was built in 1999, has 2 levels (~4k sqft)+finished basement, York Diamond 80 (4 ton) for 1st level/bsmt (split zone) and York Diamond 80 (2 ton) for upstairs. LP heat + single stage A/C in both.
The systems are old, but still in good working order. I've done some repairs (capacitors, 1 blower and 1 main board). My neighbor recently priced 2-stage replacements (similar home/same Yorks) at $15,500 for both systems (Bryant 4-ton, 16 seer and 3-ton 17 seer). I asked their contractor if he did Manual J for them, but no response yet.
TIA!
Attached Images
File Type: jpg System1-1st fl-bsmt.JPG (215.5 KB, 45 views)
File Type: jpg System2-2nd fl.JPG (206.8 KB, 45 views)
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Old 08-09-2017, 07:45 PM   #20
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So, we are going with the variable system as the cost is not much more than the dual stage system and they guy said the variable is a noticeable improvement over the dual stage and the dual stage is noticeable over the single stage... ...
That's where I ended up last year, when I was posting about my HVAC replacement. I was really focused on comfort for the A/C - we wanted good humidity reduction (generally requires a smaller unit that runs a lot), and we also wanted "burst" capacity if we had a large group over on a hot day (requires a LARGE system). We ended up with a near top-of-the line configuration. With the rebates, each extra step up wasn't that much. And in Texas, you might see a fairly reasonable payback.

Yes, any repairs are likely to be far more expensive. I take it variable speed motors aren't a $100 commodity like my old blower. But with the 'smarts' in the thermostat, it does an amazing job of anticipating the needs, and adjusting fan speed and choosing between the 2 levels to keep humidity down and maintain the set temperature. It actually gives a little leeway to temperature versus humidity, depending on the priority codes programmed into the thermostat, it pretty amazing. I had some 'geeky fun' just monitoring what it was doing.

I also set the fan to 'circulate' in summer- that ensures that the fan runs at least 30 minutes out of every hour. So it is 'smart', if the A/C is running that much, it doesn't run the fan by itself any extra. That really helps keep upstairs/downstairs even. And 'circulate' is a very low speed, I think it only used ~ 100 watts.

So it depends on your situation and priorities, but I'm glad we went upscale with ours, and we don't even use the A/C that much here in Northern IL. It's been off for at least a week now (I still have the fan circulating, to get some air movement in the basement).

-ERD50

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