Okay HVAC guys, my mom probably needs a new system.

[cfabe]

So it seems this heat wave has stressed the A/C at my mom's house past it's breaking point. Here's what's happened so far. Sunday, the house got warm and the outside unit quit working. The unit is a 30+ year old Singer. I was out of town Sunday, but Monday I checked it out and found the contactor was burnt up. Replaced that, then found that the compressor was having difficulty starting. Sometimes it would labor and then start up but more often it would just hum and squeel for a few seconds, then go into thermal protect mode (I assume). Swapped in a good start capacitor, same thing. On a whim I upped the start cap value from 40mfd to 70, and it would start reliably, but would quit after running for about 3 minutes, then cool off for a few minutes and cycle like this. So I assume the compressor is shot. I can't think of anything else to try myself so I have a call in to our usual hvac service guy. If I'm overlooking something I can do myself, let me know.

Now the question is what to replace it with. The house is a 1964 2-story colonial, 2400 sqft, with some insulation but probably underinsulated. The current system never cooled the upstairs of the house adquately, but they never put much effort into balancing the system using the registers either. The furnace is a 20 year old natural gas unit. It's been flakey the past couple years, I had to replace the spark ignition system last year for about $150. It has been inspected in the past year or two and is still in servicable condition. Their gas bills last winter were outrageous, $500+ a month for dec-feb. Heating performance has been fine.

Any reccomendations for the new system? Just replacing the a/c would be easier on the budget but I may suggest to her to replace the furnace and a/c if it would be worth it in terms of energy usage and system performance. Right now I will probably just suggest a 13 SEER a/c because here in northeast ohio we really only use the a/c for a month or two. What about the furnace, 80% versus the 90+ condensing units. Any brands to prefer or shy away from?

Thanks in advance for the advice, will update here as things progress.

Chris

[280plus]

How long does she plan to stay with the house? I'd go the whole deal if she has no plans of moving. 90% and 13 SEER will save you some utilities money. Just be aware you can't take the 90% exhaust and put it into the chmney, the resulting moisture will condense on the chimney lining and eventually eat the mortar away. But you can vent them just about anywhere else to the outside using PVC pipe.

Personally, I sell Bryant. Same as Carrier but without the extra cost of the big name. They've been pretty reliable units and their customer support is pretty good too. Stay away from the brand x models, they're cheap but there's a reason for it. I've seen them go in as little as 3 years. Spend the few hundred bucks extra and get a midrange brand name.

[BozemanMT]

Get the whole unit
 a 20 year old furnace is just waiting to fail on christmas day at 20 below.

its' cheaper for the HVAC guys to do both units at once, then to add on one later.

My mom got an 80% furnace and a 13SEER unit for her townhome and it was under 5k (like 1500 feet up and 1500 feet downstairs) and that was just on a 13 year old unit.
The new units are amazingly efficient, your power bills will go way down.  

I have a 96% efficient furnace, variable speed, etc.  I wouldn't do it again.  I'd get the single speed 96% efficient though (the variable is weird) and man, i have low power bills. I live in a 2200 square foot ranch (not efficent) and my power bills are lower than my moms (and her smaller townhome)
I think my high gas bill last winter was 120 bucks.  My neighbors (same basic size house) was over $250.

I just got the AC installed, we'll find out with the first power bill.  I gotta admit it's pretty sweet.

i agree with not buying a no name, get a good solid brand and let them take care of you.  parts are easier too.

[K Frame]

Yep, 20 years is right at the end of the expected design life for a furnace, so replace it at the same time.

[mfree]

My Trane 90%/13 3.5 ton was $3500 installed. Just to give you fair measure.

IIRC due to codes if it's less than 90% you've got to have the exhaust tinned (meaning sheetmetal venting) but above that PVC is a-ok. My installation was also dead simple because I have a dual collection plenum that was at the floor, the unit just dropped over it and mated up with existing ductwork... and I also had them install the unit right on the other side of the basement wall, which put it under the bedroom window (I don't care, I like the white noise) instead of clear on the other side of the house. I'd rather have a 40' run of electrical cable than a 40' run of refrigerant lines.

EDIT:

another btw, when I had the unit installed, it was replacing something similar to what you have now. My utility bill *halved*... from $350 to less than $200 in the winter, and my summer utility bills went from $185-200 to struggling to top $100.

[charby]

Also think about adding more insulation to the house after you install a new HVAC system.

[Brad Johnson]

13 SEER will be your only choice anyway with all the new energy regs in place.

Consider a split system, or at least motorized dampers that can be used to better balance the system.

Have an insulation company come in and look at the house. It pays to add insulation. It pays a lot. You will actually be better off to get a 13 SEER system and add a lot of insualtion in key places than pay a bunch for a 15 SEER system and then not reinsulate.

Get a good brand system like Trane, Carrier, or Lennox. Get it installed by a well-recommended installer. As a real estate agent, most of the trouble I encounter with new or relatively new systems is directly related to a shoddy install. Going cheap here will cost you over the entire lifespan of the system.

Brad

[cfabe]

Well the service guy was out today, the compressor started right up for him and kept running. Figures. He did find a partial break in the 24v control wires from mice which he said could have let the contactor pull out briefly but that might kick the compressor off and then it won't restart for a few minutes.

So the unit is running agian, but I have a performance question. At 1pm today when the guy got it running agian, the temperature inside was about 85. The unit has been running non stop (I assume, wasnt home) for 4.5 hours now, and it has only lowered the temp to 82. Outside has been about 95. Is this acceptable performance, or is there still a problem?

[280plus]

See how it is tomorrow after it's had a chance to catch up. Realistically most AC systems are designed to hold 20* below outdoor temp so if it's 95 the best you can expect, theoretically, is 75 indoors.

Just a word of caution, we all love Carrier, Trane ain't too bad but we HATE Lennox. They have a habit of making the controls a little outlandish and most guys can't figure them out. Even their so called "Certified Lennox Technicians" I just had a big go 'round with one of their units. Suggested my customer call the local Lennox dealer, THEIR people couldn't figure it out either. I ended up ripping out all the wiring and rewired it to operate like any other normal AC.

[Brad Johnson]

rewired it

So, are you gonna change your name to Tim the Tool Man now?

More Power! argh! argh! argh!

At 1pm today when the guy got it running agian, the temperature inside was about 85.

Did the service tech measure the outlet air temp? The delta between intake and outlet air should be somewhere in the 15-22 degree range. Also, you did change the filter, right...?

Brad

[280plus]

Yea, what Brad said. 18* difference is optimum.

Actually, by the time I got through ripping out all the unecessary BS relays it was probably using LESS power.

[Mabs2]

For something that old, just go ahead and get a new unit.  These days units are much more effecient.
With rising gas/oil prices I'd reccomend a heat pump with electric backup.
If you need convincing, I can.
*edit*  Forgot to mention, for a heat pump you'd need a new duct system (Unless those guys 30 years ago were 30 years ahead of their time and did a REALLY good job and had sealants that hadn't been invented yet.).

[cfabe]

I did measure the outlet temerature after he left, and it was about 64F so about a 20 degree drop. Sounds like it's working well. The guy put the gauges on it the pressures were in line.

Air source heat pump is not an option in this climate, we typically go weeks at a time under 20F in winter. And the ducting is not adequate.

She'll probably upgrade the next time the system fails and it costs any significant ammount to replace it. I have explained all the efficiencies to her, but she's cheap and doesn't believe in replacing equipment that still works.

[280plus]

I have explained all the efficiencies to her, but she's cheap and doesn't believe in replacing equipment that still works.

That would be the story of my life!

[Mabs2]

I did measure the outlet temerature after he left, and it was about 64F so about a 20 degree drop. Sounds like it's working well. The guy put the gauges on it the pressures were in line.

Air source heat pump is not an option in this climate, we typically go weeks at a time under 20F in winter. And the ducting is not adequate.

She'll probably upgrade the next time the system fails and it costs any significant ammount to replace it. I have explained all the efficiencies to her, but she's cheap and doesn't believe in replacing equipment that still works.

Understood...
Geothermal would then be the way to go, but would include tons more work.

[K Frame]

"Realistically most AC systems are designed to hold 20* below outdoor temp so if it's 95 the best you can expect, theoretically, is 75 indoors."

Which indicates to me that my system is dramatically oversized AND coupled with a bullshit vent layout.

I can hang a side of beef in my living room and grow cultures in my bedroom at the same time.


I can easily hold a 30 deg. plus difference between interior and exterior temperatures.

[K Frame]

"Geothermal would then be the way to go, but would include tons more work."

As well as TONS more money.

The true question would be whether C's mother would ever live long enough to see the payback on a geothermal system.

[Sindawe]

Yea, what Brad said. 18* difference is optimum.

Hmmmm...that is interesting.  The central AC on my townhome must be way oversized then.  Even during the heat wave we had during the last couple of weeks here in Colorado (temps in the low 100s) the AC had no troubles keeping the interior of the home at 78 degrees F, even with all the huge south facing windows I have.  I know it could have pushed the temps ever lower if I'd wanted it to.

[cfabe]

Sindawe, I believe the 18F figure refers to the temperature difference across the air handler, not the difference between outside and inside. So if your house is 80F inside and the a/c is running to cool it down, you should have 80-18 or 62 degree air blowing out of the vents. I'm pontificating here, but I think this 18F temperature is more a function of how well matched the air handler and compressor are in terms of CFM versus BTUs while the ability to cool the house to a comfortable level even on hot days is determined by the balance of the house cooling load versus the BTUs of the unit.

Mom is 60, so she hopefully has a couple more decades of electric bills to pay, but I think she'll only be in this house for 5-10 more years. Of course if I'm still in the area I may inherit it.... so maybe I should push for the geothermal *evil grin*.

[280plus]

There are two figures going on here. When we design an AC system for a house the design parameter is that the system be capable of holding the indoor temp 20*F below outdoor temp. So yes Mike, it sounds like you are grossly oversized. What this does is cause the AC to not run LONG enough during the "on" cycle to effectively remove the moisture from the air. It cools off too fast and shuts down too soon. If it COULDN'T hold at least 20* "Delta T" (difference in temp) it would be undersized and be basically a big DE-humidifier because it will run much longer on hot days and pull much more moisture out of the air than it should but never cool the air effectively. So, you oversized folks can TRY reducing your indoor fan speed to "low" which actually reduces the capacity of the system. BUT on cooler nights if you run your A/C below say 70* indoors you MIGHT freeze up the indoor or "evaporator" coil. Put in a programmable T'stat and set it back to 74* at night and you shouldn't have a problem.

THEN there's the second figure we are talking about. Delta T across the indoor "evaporator" coil. You measure this by taking both the return and supply air temps and  subtracting the supply temp from the return temp. The registers where the air comes out are the supply and that (or those) registers that draw in the air and collect all the dust is the return(s). Anyhoo, 18* is considered optimum and it is a simple way of determining whether your system is operating at the correct capacity. Actually between 16 and 20 is considered within range but we LOVE to see 18* because that means everything is running just right. If you see it below 18* you question the capacity of the refrigeration circuit being up to par and if you see it exceeding 18* you question the capacity of the indoor air circulation system. It's not moving anough air. Most of the time this will be caused by a dirty return filter. Other parameters help pinpoint the problem should one exist.

[280plus]

I was just thinking cfabe. On real hot days when the electrical grid is stretched to it's limit we get what's called "brownout". It causes things to overheat and some compressors will have a hard time starting. Oh btw, yes there is a thermostatic switch embedded in the windings of the compressor motor that shuts it down when it gets too hot.  Brownout is actually a loss or reduction of FREQUENCY not voltage. Generally when a compressor demonstrates an inability to start on a day like that it indicates the old girl is tired. Have we talked Gas Absorption Heat Pump yet? :evil grin:

LOL...

[280plus]

Afterthought:

Never forget, a little knowledge can be a dangerous thing!

[BozemanMT]

I've got an update to my post about installing a new fancy 13 SEER
the power bill came
It covers about 15 days when we had the A/C and it's been hotter than hades all month, so it's a pretty good summer test.
we hold it at 73 degrees, it's a 2000 square foot ranch, but it's pretty well insulated.

Mypower bill is normally 30 to 35 dollars a month electric.
This month (15 days of A/C) it was $50

20 bucks for nice cooling?
that's 40 a month
yeah, I'll take it.

[280plus]

Not bad at all, I'll bet your choice to keep the temp up at 73* has a lot to do with it too. You would be on my favorite customer list.  I've had customers who'd set theirs on 80* and be just fine with it. They mock my suggestions of turning it down a couple degrees. Of course they are of the senior persuasion.

[BozemanMT]

Not bad at all, I'll bet your choice to keep the temp up at 73* has a lot to do with it too. You would be on my favorite customer list.  I've had customers who'd set theirs on 80* and be just fine with it. They mock my suggestions of turning it down a couple degrees. Of course they are of the senior persuasion.

Actually 73 is a little cold.  But you know, I paid big bucks I want to be COLD

My mom is like that, you go over there and it's like 92 degrees inside, it's like WHY DO YOU HAVE AIR CONDITIONING?
bleech.