2 Stage vs. Single Stage HVAC (Austin, Howe: house, buying, construction)

[wildflower_FL]

We are planning on replacing our current 13 SEER HVAC with a 16 or 17 SEER system, and was wondering if anyone had thoughts on the benefits of upgrading to a 2 stage system in Central Texas. Our house is a single story, 2000 SF, typical mid-90's North Austin construction.

We tend to keep the thermostat around 80, and don't usually run it at night. We run the AC the most from mid June to mid Sept, but usually don't run it much outside of that. House is positioned well to take advantage of cross breezes, so opening windows and running ceiling fans keeps it pretty comfortable.

A 2 stage system would run an additional $1500. I like the theory of it, but don't like the idea of having the AC running constantly, even if it was at a lower capacity. The biggest advantage that I read about is that it helps with humidity, but I don't find Austin or our house all that humid. Any other advantages, or would it be better to put the extra money towards more attic insulation?

Please feel free to DM me the names of any local HVAC companies that you have had a good experience with. Thanks!

[10scoachrick]

IF you need more attic insulation, you can get a tremendous amount added for ~$500 if you go the DIY route. Provided you have adequate ventilation in the attic, that would be your best barrier to the heat gain from our cenTex sun.(Assuming all the windows have shade or shades/blinds, etc)

If you don't actually run the A/C all that often(wish I could say that!), the air quality could be improved by the air exchange. If you can get away with natural ventilation, that's even better(assuming the outside air is of the quality you seek).

Seems like $1500 is a pretty tough hit on a system that will serve 2000 sq ft. Especially if you are taking advantage of natural ventilation, it doesn't sound like it would be all that beneficial to run that 'second' stage.

[tex1901]

Originally Posted by wildflower_FL

We are planning on replacing our current 13 SEER HVAC with a 16 or 17 SEER system, and was wondering if anyone had thoughts on the benefits of upgrading to a 2 stage system in Central Texas. Our house is a single story, 2000 SF, typical mid-90's North Austin construction.

We tend to keep the thermostat around 80, and don't usually run it at night. We run the AC the most from mid June to mid Sept, but usually don't run it much outside of that. House is positioned well to take advantage of cross breezes, so opening windows and running ceiling fans keeps it pretty comfortable.

A 2 stage system would run an additional $1500. I like the theory of it, but don't like the idea of having the AC running constantly, even if it was at a lower capacity. The biggest advantage that I read about is that it helps with humidity, but I don't find Austin or our house all that humid. Any other advantages, or would it be better to put the extra money towards more attic insulation?

Please feel free to DM me the names of any local HVAC companies that you have had a good experience with. Thanks!

Go with the 2 stage system, they way you use your A/C, you would be running on one stage most of the time saving big bucks. With a two stage you would still have the needed BTUH capacity for the 100 degree days when you need it. This summer was very dry. Very rare for Austin!

[cBach]

It seems like it's overkill for your needs. You don't use A/C that much and when you do you run it you don't overdo it, so it would take an awful long time to recover the cost for you.

[mark311]

Originally Posted by cBach

It seems like it's overkill for your needs. You don't use A/C that much and when you do you run it you don't overdo it, so it would take an awful long time to recover the cost for you.

I agree with cBach. So I have a two story home and recently replaced both my upstairs and downstairs systems. My HVAC guy actually sort of talked me out of going with a 2 stage system as he said it would have a much shorter life and wasn't really worth the extra money for me since my bills weren't extravagant to begin with. He had seen a lot of new 2 stage units experience problems and he deals with pretty good brands (Carrier, Payne, etc.)

I also went with 13 SEER units which were still an upgrade from my 10 SEER unit. However, from what I was told, how many tons the units are is really more important than the SEER rating as that is just related to energy consumption and that might not be as much as you think with brand new units. My HVAC guy did the math with me and I would have been looking at a lot of years (over 10 at least) before I would come close to making up the difference in cost between a brand new 13 SEER or 16 SEER in electricity cost savings. A brand new 13 SEER unit will still run much more efficiently than your old 15 year old unit.

[blakely]

Originally Posted by mark311

My HVAC guy actually sort of talked me out of going with a 2 stage system as he said it would have a much shorter life and wasn't really worth the extra money. He had seen a lot of new 2 stage units experience problems and he deals with pretty good brands (Carrier, Payne, etc.)

We recently faced this decision and also got talked out of two stage systems by several AC people, for some of these reasons.

[tex1901]

Originally Posted by mark311

I agree with cBach. So I have a two story home and recently replaced both my upstairs and downstairs systems. My HVAC guy actually sort of talked me out of going with a 2 stage system as he said it would have a much shorter life and wasn't really worth the extra money for me since my bills weren't extravagant to begin with. He had seen a lot of new 2 stage units experience problems and he deals with pretty good brands (Carrier, Payne, etc.)

I also went with 13 SEER units which were still an upgrade from my 10 SEER unit. However, from what I was told, how many tons the units are is really more important than the SEER rating as that is just related to energy consumption and that might not be as much as you think with brand new units. My HVAC guy did the math with me and I would have been looking at a lot of years (over 10 at least) before I would come close to making up the difference in cost between a brand new 13 SEER or 16 SEER in electricity cost savings. A brand new 13 SEER unit will still run much more efficiently than your old 15 year old unit.

Your A/C guy does not understand the concept of seasonal a/c heat loads and the projection of energy costs 5 to 15 years down the road. Why would you pay for the energy cost of a 5 ton system when 75% of the the time you need 4 tons of cooling. Variable heat loads calls for an a/c unit that meet the current BTUH demand at the lowest energy cost. You cannot compute payback at the current cost of energy. it is only going to go up.

[Gorfml]

why even have AC if you are going to set it at 80 degrees?...

[mark311]

Originally Posted by tex1901

Your A/C guy does not understand the concept of seasonal a/c heat loads and the projection of energy costs 5 to 15 years down the road. Why would you pay for the energy cost of a 5 ton system when 75% of the the time you need 4 tons of cooling. Variable heat loads calls for an a/c unit that meet the current BTUH demand at the lowest energy cost. You cannot compute payback at the current cost of energy. it is only going to go up.

Your information makes some sense. I didn't say how many tons my systems are. Overkill to a 5 ton system wasn't mentioned, just that how many tons is important, but almost never mentioned. People only talk about the SEER ratings.

However, I'm not going to plan for energy costs 10 to 15 or even 5 years down the road if it's going to cost me 2 to 3 times the amount up front. Two brand new Carrier 13 SEER 3.5 ton systems (all the inside and outside equipment) installed cost me $5500 total for my 2 story 2400 square foot house. Quotes for two 16 SEER 2 stage systems by other companies were over $10,000 easily.

I see it as like buying a Prius. Sure it might be the right thing to do, maybe, but it might end up costing me more money in the long run. My electric bill was never higher than $243 this summer even with the 13 SEER units running almost all the time since it was 100 degrees almost every day. Would my cost savings really had been that much more with 16 SEER units?

[wildflower_FL]

Our current system is a 5 ton system, which is oversized for the house. We will be moving to a 4 ton system. I really do like the theory of having a system that runs at a lower capacity outside of peak times, but I am not sure how well that translates given Austin's climate. I posted this because I was curious what other Austin residents thoughts were.

One of the HVAC reps I spoke with showed me a chart from Trane that illustrated how their 2 stage system works with Austin's median temperatures. According to the chart, the lower stage would run most of the time during the months of April, May and October and it would run at full capacity from June - September. From the chart, it doesn't look like there would be much of an advantage unless you desire to run the HVAC year round.

Austin is a pretty cold climate compared to what my husband and I grew up with, and as a result, we don't find heavily air conditioned spaces comfortable. Our house will top out around 84 with no AC in 100 degree weather. That is a bit warmer than we want it, so the AC is getting replaced.