hvac: variable speed, 2/1 stage, R410A/R22, 80/90% decisions

[Todd H.]

Greetings,

It's that sad time to replace a furnace and possibly the A/C at the same time. I've done my googling of past threads and gathered bits and pieces, but thought I'd offer up my situation all the same. The location is Chicago, IL, home is a 15 year old 2-story colonial around

2300sf, with a 15-year old 100,000 BTU furnace and a 3ton A/C unit. Summers get hot and obnoxiously humid, but aren't that long. Winters are, well, Chicago winters.

I'd like some thoughts on the conceptual stories being spun by two quotes I've received thus far. Sadly, the two companies seem to have divergent advice on several points!

o Company A: a large well-respected 2-location Carrier dealer in Chicagoland that has a training budget and a large staff of technicians. Thought of well by every home inspector I've come across.

o Company B: The other company, a lesser known, a 2 co-owner Frigidaire dealer recommended by a friend who knows them very well. The friend is one of those sorts who can do ANYTHING to his house and just got done rebuilding it literally from the foundation up largely on his own, and chose these guys for HVAC.

The questions:

1) Carrier vs Frigidaire. Carrier I've had and had pretty good luck with. Frigidaire...never even knew they did HVAC. Thoughts? I'm leaning heavily Carrier or Bryant on this one.

2) 80 vs 90% The larger Carrier dealer interestingly was recommending 80% for my 15-year old home. They said if it were new construction 90% would make a lot of sense to save on running a flue to the roof, but given that we already have one, it was probably more cost effective to go with 80%. The Frigidaire dealer said the 90% was the way to go with the number of degree days we have here in Chicagoland. I'm more inclined to lean toward 90% because I don't see energy getting anything but more expensive in the future.

3) Variable speed vs fixed speed fan. Carrier dealer recommended against variable speed for my ductwork. He did not recommend the variable speed motor for my ductwork because it went from square ducting to round ducting ,and something about the turbulence caused by the transition causing the motor to run at higher speeds for longer than it should--some mention perhaps of a sensor of some sort? How do Carrier's variable speed motors work?

The Frigidaire dealer was very pro-variable speed, although they couldn't seem to explain to me my question about "what dictates the speed the fan runs during a cycle? Is there a sensor? Is it timed?" They told me a lot about dip switches for setting mins and maxes, but never did manage to "get" that I wanted to know the control algorithm for the fan speed so I could make sense of maybe why they were all for variable while the Carrier guy was not.

4) Dual stage furnace vs single stage. The Carrier dealer, who'd ruled out variable speed based on my duct configuration, said a 2-stage would bring me more comfort and evenness of heating temp. The Frigidaire dealer wasn't pushing 2 stage since variable speed addressed the comfort issue.

5) 13SEER vs 15SEER. If it only cost $300 more, would ya do it? Carrier dealer had this option for mein the quiet Performance series (I like quiet given the configuration of my yard and its use i the summer). Both dealers seemed to feel the federally mandated 13SEER was plenty efficient for our area. In the Carrier dealer quote, I had 13SEER comfort and 13SEER performance options with a $300 spread between them for the better noise package. Another $300 gets me to 15SEER and quiet.

6) R410A vs R22? Carrier dealer recommended the R410A versions of their units vs the R22 as it was only $75 more to get the more eco-friendly refrigerant that'd be around for the forseeable future, plus the R410A units were a lot more reliable and had longer warranties because they cooperate with lubricants a lot better than R-22. The Frigidaire dealer was quiet on this issue as they didn't appear to have any R410A units available.

7) Do furnace and A/C simultaneously? Or not? One one hand I'd like to hold onto the $2500-$3500 the A/C would cost rather than dropping that into the bucket now. The Carrier dealer said I would only save about $250 in installatoin labor by doing them both at the same time. The Frigidaire dealer seemed to push at least replacing the A/C coil with the heater even if we waited on the outside unit. The A/C currently seems to work well now, though we do have a pretty good temp difference upstairs and down even when running our current single speed blower 24/7. I don't see a new unit making any difference in comfort, but we would see a few months of energy savings.

Company #3, another larger place, comes tomorrow.

Thanks so much for any thoughts or advice with these issues!

Best Regards,

-- Todd H.

[Richard J Kinch]

R-410a must be run at much higher pressures than R-22, so it tends to be

*less* reliable. The "cooperate" and "longer warranties" stories are the big-lie approach, kind of like selling a lawn mower as being "quiet".

HVAC dealers tend to be like bankers selling mortgages. Somehow you will be saving money by giving them all the money you have.

Be suspicious of any efficiency claims that justify tearing out a working system. Ask them if they'll guarantee your electric bills will go down that much, as opposed to just hand-waving.

You know, the energy crisis was in the 1970s. In the late 1970s and then the 1980s and after everybody bought efficient systems. The efficiency "improvements" since then have much to do with tricked-up measurement schemes. Be suspicious of anyone who asserts your old system was inefficient cuz nobody cared about efficiency back when it was installed, or that everything in the 80s or 90s was inefficient.

This dealer's Web site has a good analysis of the R-410a claims:

[MLD]

Went through the same issues about two years ago. If you don't mind will respond at the bottom of each of your questions. MLD

I had a 100,000 BTU (original furnace) that was replaced with a 60,000 BTU. The original furncae was very over sized and obviously my house didn't have the benefit of a heat load calculation. When it was built (1961) they just threw in something that was sure to be more than what was needed--gas was very cheap then.

Didn't get or hear very good comments about Carrier, Bryant seemed to be one of the better ones along with Trane. I ended up with a Trane 92+% variable speed, two-stage furnace. As important as the Brand of furnace are the people who install it. I had isssues of crappy work that had to be redone.

Being in a cold climate you would be much better off with a 90+% furnace. Sure, you need to put inlet and outlet pipes (PVC) through the side of you house--you'll also most lilely need a condendate pump. With an 80% about

10-12 cents of every heating dollar is going up the chimney. Also add the folllowing to your heating costs-- The combustion air for the 80% is being supplied by inside air--air that you've already heated to 70+ degrees and are now throwing up the chimney--wasted $$$$.. This combustion air also has to be replaced (and heated, more wasted $$$$) so the result is a more drafty house and one that requires a great deal of humidifying--

I don't have a two stage thermostat so can't take advantage of some of its features. Having said that--I think that you would still be much better off with a two-stage furnace and variable speed fan. With this configuration, when the stat calls for heat it starts off on the first stage (somewhere around 60-70% capacity, not too sure ) and low fan speed. Since I don't have a two-stage stat, I've set the dip switches such that if the set temperature is not satisfied after 10 minutes, the second stage kicks in and the fan ramps up to it's high speed setting. On cold days the furnace comes on more often but most of the time it doesn't get to the second stage. The end result is a more even house temperature with the typical hills and valleys no longer evident. Additionally, since the combustion air is coming from the outside the house is not as drafty and requires less humidification. Don't have to fill the humidifier water bottles as frequently as before the new furncae installation.

[udarrell]

Hi Todd, A new home in 1991 & they did not install the A/C system so that the upstairs would be properly cooled! That ought to be the first item you have them address.

What SEER is the unit installed in your home? Ten-SEER or above & working good, forget replacing it, as you probably NOT see any appreciable savings. A 10-SEER is usually better at reducing humidity & they are good functioning units.

Do not fall for all the hype about "potential" savings, as even the

15-SEER may not work well with your conditions., They can not guarantee that those SEER levels will save you any money or provide as much or more comfort than the existing unit.

If you decide to change, Stay with R-22 &a 13 or no more than 14-SEER, and demand a scroll compressor & a TXV refrigerant metering device!

Your website is great, my websites go back to that era, too.

If you just change the E-Coil, get a good one with a TXV metering device! Changing th coil now could save a lot of extra expense later.

- udarrell

[trader4]

Are you for real? No savings from replacing a 10 SEER system with a

15? They can't even legally build 10 SEER anymore, for obvious reasons.

The SEER rating has nothing to do with ability to control humidity. A variable speed blower is a key to that, however not sure how much of an issue that would make in Chicago, or if it's worth it. Variable speed is most effective in removing humidity on days when it's not that hot, but very humid. In Chicago, when it's humid, it's usually also hot enought that the AC is gonna run enough to remove the humidity without a variable speed blower. One thing I would keep in mind is the variable speed motors and controllers cost a lot more to replace if they fail.

15 SEER vs 13 SEER means that the 15 SEER system will put out 15% more cooling with the same amount of electric used by the 13 SEER. Not sure exactly what you mean by his current conditions, but if you mean things like installed ducting that may be inadequate, then I agree the SEER rating is not gonna fix that. But a higher SEER unit installed with the same ducting is sure as hell going to use less electricity for the same cooling output.

If SEER is just pie in the sky, why are many electric companies offering rebates to get them installed, thereby lowering peak demand?

[John Hines]

I dunno. I got a Lennox a couple of years ago, with the variable speed. It works great, barely noticeable. I let it run all the time, so the air circulates through the house and gets filtered.

For a SWAK I'd say its a combo of both. If the heat is on for more than xxx seconds, increase the fan speed. When the furnace cools down, shut it off.

The only time I've seen the second stage heat kick on, was when they tested it after the install. Unless you have wide swings, like setting back the temp during the day or night, it should hardly run. Which is good, cause it throws a LOT of heat in a hurry.

Sounds well worth it.

Yeah, have them do all the plumbing a duct work at once. Why have things torn up twice?

The Air Conditioning and Heating Company Inc . did my Trane install out in the western suburbs

-- Silly sig to prevent isp ad

[Todd H.]

Is there any words missing in the sentence above? I'm surprised if you heard bad things about carrier but good things about Bryant since I hear from so many people they're made by the same company and nearly identical? Trane I hear goods tuff about too. Frigidaire is a complete unknown to me.

I ended up with a Trane 92+% variable

I hear ya!

Thanks for the response and experiences.

[Todd H.]

As a followup, thanks to all who offered advice! Got 2 more quotes (a Bryant dealer and a Ruud dealer) and ultimately decided to not do the A/C since my 10SEER unit was working fine though this very hot summer.

I decided on a Bryant (Carrier with less marketing overhead, best I can tell) 2-stage 94%, variable speed 80,0000/52,000 unit installed by a company holding the highest Bryant certification level in the area. The person who quoted it also took the most time looking at duct counts and sizes, vent opening counts and researching the existing unit's output. Their quote included the 10yr parts/labor warranty from Bryant, and I also went for the evolution control which probably wasn't necessary, but given that the quote was also $1000 less than the Carrier dealer's quote on the same system. Who knows, maybe being able to get humidification while the heat off will be nice thing.

The unit goes in tomorrow and hopefully there'll be no surprises.

And as a folloup to teh variable speed question, the Carrier dealer when I preseed him on why he didn't think variable speed would be a good fit here with my ductwork backpedaled and couldn't much recall the system he'd quoted 10 days earlier. He didn't spend a huge about amount of time here doing the quote, so perhaps he was in crank out a low quote on an inexpensive furnace and move on mode. I'm not sure.

Thanks again to all who responded with helpful info.

Best Regards,

-- Todd H.