[topcat57]

I have a 3350-sf house in the Memphis area w/ 2060 sf on 1st floor and about 1300 sf up. Have decided to replace both 19-year-old systems w/ Goodman. (Downstairs unit bit the dust last fall so we're just going to replace everything.) I've researched other brands and have decided based on better warranty, testimonies of people I know personally who have gone w/ Goodman and those who service them, that I can get more for my $ w/ Goodman.

The current 4-ton downstairs A/C was never able to keep up when it exceeded 80 degrees outside. A manual J done last year calculated 4.5 tons down (high ceilings, a lot of unshaded southern and western exposure), but of course they don't make that size. Installer is going to enlarge some ductwork (which will currently handle 4.5 tons) and returns to handle 5 tons. Going from 2.5 tons to 3 tons upstairs since the manual J indicated about 2.75 and the ductwork will handle 3.

I'm working with a reputable HVAC company and fully understand that a good installation is 99% of the job which I'm satisfied they will do -- they've been in business over 50 years, good BBB ratings, weren't the lowball bidder, and put sufficient time into evaluating exactly what we need, but Goodman isn't their "premier" brand so I wanted to do some research on my own. After all, this is a very big investment, and I want to get it right so I ask a lot of questions and "trust but verify" just for my own peace of mind.

We live downstairs virtually all the time and like it cold in the summer. Keeping air circulating and humidity (and utility costs) down are the important considerations. We don't keep it too warm in the winter.

Because all the larger Goodman 95% furnaces are 24.5 inches wide and therefore will not fit through the attic stairway (even if it were to be torn out), we're having to go with the 80% units. Since we pay only a few hundred $ a year on gas for heating, I've calculated the savings between the 95% and 80% would be very little, and we'd already decided to go with the 80% upstairs anyway. Our real utility savings should be on electricity in the summer.

Here are the combinations I'm considering.

DOWNSTAIRS: DSXC16 (2-stage) + GMVC8 (VS, 80%)

I'm pretty sure of the downstairs system. The only option would be to go with the 18 SEER (DSXC18) which makes about 8% difference in the cost of the whole house system. (I don't think I'm breaking any rules by saying that.) So I think the only question I have to consider is, assuming plugging other sources of energy loss (insulation, weatherstripping etc.), would the 18 SEER give enough energy savings to recoup the price difference in a few years? I'm thinking not since we're paying around $1000-1200 a year on cooling now (about 8.5-8.8 cents/kwh) and that's with only an 8 or 9 SEER system (and a 19-year-old one at that). Just going to a new 2-stage, 16 SEER unit should take a chunk out of that.

I installed touch-screen programmable thermostats 4 years ago (I don't program them, they're just a lot easier to read and look very cool ) but I wasn't planning to replace them w/ the Goodman ComfortNet thermostats which would involve running extra wiring. According to the installer, new thermostats would not result in any energy savings. Are there any other advantages of installing the ComfortNet thermostats besides just being able to see more information (diagnostics, etc.)? Are they necessary to get the full benefit of the 2-stage, VS system? (I've gotten conflicting answers to this.)

As for the furnace, the manual J done last year indicated around 95-100,000 BTUs. This installer seems to think 90,000 is enough. He's going to do his own manual J which may provide a more exact number, but if it still comes out about the same (say, 100,000), would the 115,000 BTU be overkill? (Those are the choices w/ Goodman -- 90,000 or 115,000.) Not sure what sizes we have now, but even though we don't keep it too hot in the winter, there are some very cold areas, particularly on the shaded, north side of the house which is at the far end of the duct run.

UPSTAIRS:

Several things to consider here which is where I'm conflicted and need advice.

Can't decide if 13 (GSX13), 14 (SSX14), or 16 SEER (SSX16) along with the GMH8 furnace is the way to go or if the 16 SEER 2-stage (DSXC16) w/ the VS furnace would provide enough of an improvement in temperature stability and humidity control to make it worth the extra $. Just going from 2.5 tons to 3 should make some difference as will going to even a 13 SEER, but trying to decide if the 2-stage compressor w/ VS blower, even though we don't live upstairs that much, would help even out the whole house by providing a better "buffer" between the roof and the downstairs.

The manual J indicated a 60-70,000 BTU furnace upstairs which makes me think the 90,000 downstairs sounds a bit small in comparison.

One last question about the upstairs furnace. Does the GME8 (w/ the XE13 motor) really provide much in the way of energy savings over the standard motor in the GMH8? Installer says his Goodman distributor doesn't stock the GME8.

Sorry to be so long-winded. Any practical advice would be much appreciated.

 

[sktn77a]

Two stage is definitely the way to go for both heating and cooling. As dehumidification is important in your neck of the woods, running on low for longer periods will be better, especially if the unit is a little oversized. Bear in mind that hot air rises so you upstairs will get a significant heat gain from the downstairs furnace so there is probably no need to oversize the upstairs furnace.

 

[beenthere]

The Comfort net stats shouldn't need anymore wires then what you have. Except to the outdoor units. And since your going to 2 stage units, you need more wires to the outdoor units anyway.

Comfortnet will be able to slow the blower down to control humidity. Your current stats can't.

Ask your contractor to check your duct systems static pressure.

I know. He told you its sized for 3 tons. Have him verify it with a static pressure test.
He can check your current static with your 2.5 ton. And calc how much it will be with a 3 ton system at 1200 CFM.

VS blowers can make undersized duct systems loud.

While if your current duct system is moving 1000CFM at .6 static, and increasing to 1200 will only increase it to .86"
If it currently only moving 900CFM at .6", increasing CFM to 1200 will increase static to 1.07". And it will use more electric then a standard blower.

 

[topcat57]

Thanks, sktn77a. It was the downstairs furnace I was questioning the size of. The manual J someone did last year indicated about a 95-100,000 BTU for downstairs. This installer (who will do his own manual J) thinks a 90,000 BTU is sufficient for the downstairs. So if this manual J indicates something between 90,000 and 115,000, I wonder if we should oversize by going w/ the 115,000 or risk undersizing by going w/ the 90,000.

So you think even though we don't live in the upstairs space nearly as much, the 2-stage, VS upstairs would help even out the whole house? We're definitely going with the 2-stage, VS downstairs, but I'm trying to decide if going w/ the same thing up is worth the extra $. It does feel pretty humid up there in the summer, but it's only a 2.5-ton system, and an old 8 or 9 SEER one at that. Regardless of whether we go w/ a 13, 14, or 16 SEER single-stage or the 16 SEER 2-stage, VS, anything will be an improvement. I'm just trying to decide if the latter would make a difference in the entire house. The entry hall in the center of the house is open to the second floor and a lot of warm air gets sucked up there, especially in the winter.

 

[topcat57]

Thanks, been there. Very helpful information. I believe he did say he was going to do a static pressure test, but I'll ask him to do it if he doesn't.

I thought the ComfortNet thermostats would require extra wiring be run. (I looked the other day to verify what I remembered. RC is jumpered to RH, then W, Y, and G -- 4 wires.) I read somewhere they require 10 wires, and an installer told me they'd require more than 4. But you're correct. I just looked at the installation instructions for that thermostat, and they require only 4 wires inside (which just goes to show, don't believe everything you read or hear).

I just looked at retail $ on these things... :eek2:. Two ComfortNet thermostats are going add about 8% to the cost of the entire system!

Are you saying that the 2-stage, VS features of the A/C and furnace will not work at all w/o these thermostats? It sounds like you're saying if I don't replace the thermostats and they install the 2-stage, VS units, I'll still only have the equivalent of a single-stage, single-speed system in which case I would be better off to just buy the single-stage A/C units (SSX16 vs. DSXC16) and two standard furnaces.

When this installer was pricing a Carrier system I understood him to say the Infinity A/C he recommended would require a new thermostat to get the VS feature, so I wondered why the Goodman 2-stage, VS would not.

 

[john_ertw]

Just a homeowner, but go with the 115,000 furnace as the 90,000 will not keep up on the coldest days. Unlike a/c's which you typically slightly undersize, a furnace should be slightly oversized (based on CSA F280... the Canadian equivlant to manual J).

Also, is the manual J calc the output btu's required or input? if input is that for a 80% furnace or 95%?
As for thermostat, beenthere's recommendation of using comfortnet is a good one since it will be able to take full advantage of the equipment you are purchasing...goodman designed their new systems with that thermostat in mind... similar to how higher end carrier systems should get an infinity controller.

have you thought about a heatpump with an air handler instead of a gas furance? I'm not sure if it's suitable in your area, but you said your heating bills are fairly small. it may reduce your overall costs. again, i'm not sure if a heatpump is a good idea in your area though.

 

[topcat57]

I've wondered about a heat pump, but since nobody has ever mentioned that as an option and since our electricity is higher in the summer than our gas is in the coldest part of the winter, I imagine going all-electric would make our utility bills higher in the winter than they are now. We already have an all electric kitchen (don't cook a lot) and dryer and gas water heaters. I think if a heat pump were a reasonable alternative someone probably would have suggested it already.

Thanks for the information about the thermostats and furnace.

Can any furnace keep up on the coldest days in Toronto?

 

[beenthere]

Any 2 stage thermostat will operate the staging.
But, you won't have the VS blower control of the communicating thermostat.

I find it hard to believe that Memphis gets so cold that you need such a large furnace.

Also. What temp do you set your thermostat for in the summer.

 

[topcat57]

Downstairs thermostat is usually set on 74 in the summer. When the downstairs A/C was still working it would be 80 degrees at the thermostat with the A/C running full blast continuously. Occasionally when it cooled off enough outside to actually keep up I'd set it on 73 just to cool the house down some more, but I could have set it on 79 or 80 and accomplished as much when it was in the 80s or 90s outside. (It even tops 100 occasionally.) If I'm moving around much inside I can comfortably set it on 70 or 71.

If it's below about 50 outside we keep the furnace set on 71 (72 if it drops below 35 or 40) and turn it down to 68 or 69 at bedtime.

Those are all downstairs values. Unless we have company or are working upstairs, I set the A/C up there on about 76 or 77 and the heat on 66 or 67.

You may be right about the furnace. That seems to be what the installer is thinking. Some guy wanted to put in a 130,000-BTU furnace last year! Lowest winter temp here is 10 degrees F, but that's very rare. We had an extra cold winter this year and hit 10 a couple of nights. Usually it doesn't get below the teens at night. We'll have a few days every winter where it doesn't get out of the 20s during the day.

I understood the installer to say the price for the same size 90,000 and 115,000-BTU furnaces is the same if that makes any difference.

 

[beenthere]

4 tons should have handled your 2060 sq ft on the first floor(515 sq ft to the ton).
And now they want to drop to 412 sq ft to the ton?

I think you got problems other then it being undersized.

Possibly the duct is too small. And your only getting 3 tons of capacity from it.

You might want to also consider upgrading your homes insulation. So you can use a smaller A/C.

Insulation saves you money year round.
Sealing your house will also save you money on heating and cooling.

Going from 6.5 tons to 8 tons for a 3360 sq ft house doesn't really make sense.

My place is smaller. Only 1650 sq ft. But using the same sq ft per ton. I would need a 3.25 ton unit. I have 2.5 tons. And its over sized( It was here before me. And I'm to cheap to change out a perfectly fine working A/C). I could get a way with a 1.5 tons because of the shade I have.

Although last Oct my neighbor just cut down a lot of the trees that were giving me shade . So I might now need 2 tons.

 

[bob_scheel]

I've wondered about a heat pump, but since nobody has ever mentioned that as an option and since our electricity is higher in the summer than our gas is in the coldest part of the winter, I imagine going all-electric would make our utility bills higher in the winter than they are now. We already have an all electric kitchen (don't cook a lot) and dryer and gas water heaters. I think if a heat pump were a reasonable alternative someone probably would have suggested it already.

Thanks for the information about the thermostats and furnace.

Can any furnace keep up on the coldest days in Toronto?

Whether a heat pump makes sense depends on your electric rate vs your gas rate. I went to a single 5 ton heat pump to replace a 3 ton and a 2.5 ton pkg that did my house. LP gas cost to heat my house was $4000 / yr. Electric cost to heat is now less than $1000 / yr. (electric strip heat for the auxilliary heat) LP cost was $2.50 / gal my winter time electric cost is now $.04 /kwh thanks to separate metering and my utilities winter time heat rate. Natural gas (if I could get it) would have costed $1800 / yr to heat my house. (a little less than what I would pay for my electric if the utility didn't have a winter heating rate program.)

FYI my house is 3300 sq ft. 5 bedrooms 3.5 baths and I have a 3 seasons room with a lot of glass that we heat thru the winter (my wife has a lot of plants that I have to keep happy)

Your 6.5 ton calc seems a little high as my systems maximum heating btu is 60,000 and my AC is mostly on stage 1 during the summer. It only goes to stage 2 to catch up and if we have a lot of people in the house opening doors etc on really hot days. Definitely get 2 stage compressors and variable speed blowers on both if you are going to go that large otherwise you may have humidity problems.

 

[john_ertw]

Can any furnace keep up on the coldest days in Toronto?

We have a 90,000 btu 95% furnace for our 2 storey plus basement that is slightly larger than 2800 sq ft (each floor is ~1400 sq ft). Our insulation may be better than yours (R32 in the attic and R12 in the walls), but the furnace size you said is crazy big. We could have gotten away with the 70,000 btu furnace as our furnace never used high stage this past winter except when heating up from a lower temperature when we were out. This includes the days we were hovering around 0*F. We went with the 90,000 because that's what all the contractors told us (we had 5 visit and I probably spoke to another 15 on the phone who I wasn't comfortable with their knowledge) and our previous furnace was a 110,000btu 80% model so there was some comfort there.

 

[topcat57]

Well, if they made 4.5-ton and 2.75-ton A/C units we wouldn't have to consider anything larger. Seriously, those are all good points, several of which I've wondered about myself. I know I need to add some insulation and seal around some windows and doors, and I've no doubt the ductwork is less than optimum size. It's what the builder installed when the house was built, and I'm sure they did the bare minimum.

I also think that if you asked 20 HVAC contractors come out to give you an estimate you'd get 20 entirely different opinions. It's impossible to compare apples to apples when one guy is selling apples, another oranges, and another grapes. I called 3 last fall and 4 this year, one of whom I never heard from after he came out, and talked with a 7th by phone only. No two have made close to the same recommendations. Three, when they looked at the outdoor units said, "Ya wanna replace these with the same sizes?" **spit** Hello? Isn't that the contractor's job to calculate the appropriate sizes and make recommendations?

Most have recommended the 5-ton/3-ton combination, but they're all over the map on duct needs, SEER ratings, other features, and of course brands. Only two have so much as mentioned furnace sizes. And the guy I'm going with learned from his distributor that the dimensions on the larger-BTU 95% furnaces made it impossible for them to fit through the attic stairway opening. I suppose all the others would have just ordered the equipment and learned when they tried to install it that it wouldn't fit. At least this guy seems to think beyond the end of his nose. Some say the existing ductwork/returns will handle 5 tons, others say the ductwork needs to be enlarged and/or returns added, another says just go w/ a 4-ton down and cut off the vents on the cold side of the house in the summer to force more cold air back to the hot side, two wanted to put in a zoned system with electronic dampers (big $ there), add manual dampers in the attic ductwork, and on and on and on.

I've already been burned by three contractors (not HVAC) in the 4+ years I've lived in this area, and I thought I had vetted them all thoroughly. (So much for multiple references including those from friends and family.) It's been my experience that contractors around here are not known for their honesty or skills, so excuse me if I seem a little gun shy. I trust the guy I'm going with, but at the same time I still want to make sure I'm an informed consumer about the product.

Might I suggest you add the smilie of the little guy frantically pulling his hair out? Or the one of the little fella banging his head against a brick wall. Either would be appropriate right now.

 

[topcat57]

Our insulation may be better than yours (R32 in the attic and R12 in the walls)...

In my dreams. R19 in attic, I think. Not sure about the walls.

 

[beenthere]

You should do the insulation and air infiltration improvements first. Before you spend lots of money on a larger system that you don't need.

Did you do your own load calc. Or did a company do one and tell you that you need bigger equipment?

 

[topcat57]

I'll definitely be doing that ASAP, but we've got to have A/C very soon. It's been in the mid-80s here, and it's been pretty miserable this week.

There was very little difference in price between the 4-ton and 5-ton, but I get your point about not buying more than we need.

The manual J was done by a contractor last year. I didn't see the results. I've only used the online calculators and got numbers pretty close to what they said the manual J showed (4.5-ton down, 2.75-ton up). The contractor I'm using will do another one, but I may try to slog through HVAC-Calc and do my own, too. This is like paying a doctor and having to make your own diagnosis.

The others who've recommended the 5-ton have mostly based it on square footage, ceiling height, lack of shade on the south and west sides, and the fact that the 4-ton has never kept up.

 

[bob_scheel]

I'll definitely be doing that ASAP, but we've got to have A/C very soon. It's been in the mid-80s here, and it's been pretty miserable this week.

There was very little difference in price between the 4-ton and 5-ton, but I get your point about not buying more than we need.

The manual J was done by a contractor last year. I didn't see the results. I've only used the online calculators and got numbers pretty close to what they said the manual J showed (4.5-ton down, 2.75-ton up). The contractor I'm using will do another one, but I may try to slog through HVAC-Calc and do my own, too. This is like paying a doctor and having to make your own diagnosis.

The others who've recommended the 5-ton have mostly based it on square footage, ceiling height, lack of shade on the south and west sides, and the fact that the 4-ton has never kept up.

There could be several reasons why your old 4 ton couldn't keep up that are not the result of it being undersized. Badly installed / leaking ductwork is a prime example. Bad valves in the compressor, dirt plugging the coils, debris in the refrigerant piping, etc. etc. Having too large of a unit can be worse than having one too small. Mold does wonders for the resale value.

 

[topcat57]

Mold does wonders for the resale value.

Point taken. Thank you.