Is multi-stage HVAC worth it?

[dat2109]

I'm needing to have my A/C replaced because its 14 years old and started leaking freon. The furnace is the same age and as far as I can tell working okay other than some noise that might just be the install.

My question is about upgrading from a basic single stage to multi-stage cooling and variable blowers. Is it just going to be more expensive for little return or a whole house comfort improvement?

Currently, the A/C is single stage single blower speed r-22.
The furnace is an 80% single stage natural gas.

I've had a 95% furnace before and noticed the savings over an 80%.
I don't think I've ever had a/c better than 13 seer, if even that.

To just replace my a/c I would be going with a 14 seer single stage unit.
The next step up in efficiency seems to require a multi-speed or variable (communicating?) blower fan and that's part of the furnace. I don't know if they make retrofit kits or something else to keep the furnace going. Otherwise, it seems I am going to need to upgrade the furnace too.
The final step up would be variable blower speed with a two stage compressor.

 

[yeldogt]

Sometimes it worth fixing a leak .. especially if you are not going to get much out of the replacement.

While the more advanced systems do save energy -- it's really a comfort equation as much as anything else IMO when you get into the multi-speed units.

You have to have a VS blower to take advantage of the multi-speed -- they go hand in hand with a modulating furnace / and or Heat Pump.

The better stuff is silent -- you don't hear it .. and it's able to run based on what needed vs on and off. If you are in a humid area the multi-speed AC units can run on low with a reduced fan and pull all the humidity out of the air.

I did carrier two speed back in 05 -- my two recent have been the Carrier 5 speed.

 

[theoldwizard1]

It depends a lot on where you live.

True, variable speed blowers (for residential, these are likely brushless DC motors) are expensive. 10 years ago when my son was installing a new system they told him it was not worth the additional cost. They also recommended going with one step down from the highest efficiency A/C compressor. We simple do not have a long enough cooling season.

 

[yeldogt]

It depends a lot on where you live.

True, variable speed blowers (for residential, these are likely brushless DC motors) are expensive. 10 years ago when my son was installing a new system they told him it was not worth the additional cost. They also recommended going with one step down from the highest efficiency A/C compressor. We simple do not have a long enough cooling season.

Some of the warranties are 12 years now -- or lifetime on the condenser. And that highest efficiency 10 years ago has been eclipsed a few times. I would still worry more about leaking vs replacing boards or motors ... nothing is cheap today.

The OP is thinking about a two speed -- the scroll in many of them is only about 1/3 down on low .. I forget what the Amana unit does on low. Some companies have more than one two speed.

In my case I could not justify going to the full VS compressor -- that's why I went with the oddball 5 speed. That compressor is made by Toshiba -- and they make a lot of them.

 

[metaldad]

fix the leak.
the new equipment out, is made to last warranty.
stuff is not inexpensive to repair, and thats IF the part is available.
aint worth the headache of trying to pinch a percentage point or two.
payback, isnt there.
im a hvac contractor.
replaced my stuff 2 years ago.
r22 system, i forget the seer, 13?, 95% furnace, single stage, no variable speed
and, i have every part on the shelf.

 

[58Yeoman]

An electrician friend of mine built a new house a few years ago and installed a 90+ furnace/ac. He told me that he bought a circuit board for the furnace right then, just in case it isn't available later.

 

[dat2109]

It is looking to me like a conversion variable speed blower fan does not exist for the old single speed Lennox furnace.

I also found this calculator that is telling me that unless the upgrades are less than $1500 it won't likely pay off in my circumstances. I'm in the midwest where while it does get hot, I don't use a/c 12 months a year. http://www.airinnovationsllc.com/energy-savings-calculator/
* I have no idea how accurate that calculator is

 

[ItsNemo]

I've got a 97-98% efficient variable speed modulating furnace (top model from tempstar), worth every penny and if/when it dies I will replace it with another one with the same capabilities. It's absolutely silent, the entire house heats/cools evenly, and given the size of the house and the climate here it's extremely cheap to run (helps that the house is R-22 walls and R-60 attic).

On the AC front, being that I'm in Canada, I only did a 13 SEER single stage unit...keeps the house plenty cool with reasonable cycle times and is able to knock down the humidity pretty well. The blower will vary it's speed to dehumidify depending on the settings on the communicating thermostat but you can't vary the compressor itself. I'd probably do a slightly more efficient (14-15 SEER) two stage if doing it again though.

 

[dat2109]

@ItsNemo How do you like the way the blower varies its speed while the a/c compressor runs at a single speed?

 

[dat2109]

A did a little digging and many 2 stage furnace will run in legacy or non-communicating mode, no idea if it is a good idea though.

 

[Done That]

Comm isn't needed for two stage, legacy is fine, but best to use a true 2H2C thermostat in that application.

 

[truckman5000]

All depends on location, existing conditions, $...
Where i am people want 2 stage gas, where some guy in the past dicked a gas furnace in 5 years ago in place of a 80 year old oil furnace.. In turn the home has 300 cfm air flow and people are putting in 900cfm units sized to the home. So the variable speed blowers and or controlls, high limits **** the bed all the time..Due to retrofitted in the wrong applications.
Id fix it if it were me...but get a jackass havc guy and it may cost allot of $ to find the leak and repair it correctly.

 

[ItsNemo]

All depends on location, existing conditions, $...
Where i am people want 2 stage gas, where some guy in the past dicked a gas furnace in 5 years ago in place of a 80 year old oil furnace.. In turn the home has 300 cfm air flow and people are putting in 900cfm units sized to the home. So the variable speed blowers and or controlls, high limits **** the bed all the time..Due to retrofitted in the wrong applications.
Id fix it if it were me...but get a jackass havc guy and it may cost allot of $ to find the leak and repair it correctly.

Luckily mine was in a new build with properly balanced and fully taped/sealed duct work.

@ItsNemo How do you like the way the blower varies its speed while the a/c compressor runs at a single speed?

I mean ultimately it's fine...heat is obviously variable blower and modulating burner which works perfect, with cooling the blower doesn't vary during a cycle (at least not as far as I've noticed)...there are some settings/setup you can do to pick max cooling vs max comfort vs max efficient vs fixed speeds and it knows the tonnage of the AC unit and such. In the summer I usually run the blower on low speed (ya, can pick speeds from the thermostat) 24x7 to circulate the air and balance the house and the AC unit kicks in when above set point like normal and usually gets a decent 15ish minutes runtime cycle.

 

[alexb2000]

I have a Lennox DC variable speed unit and I wouldn't ever to back to a regular unit. I have a 10 year parts and labor warranty, if it dies after that, I'd buy another one.

It is QUIET, you can barely hear it running standing right next to it. I used to wake up when the A/C kicked on at night.

In spring and fall here in Texas we have cooler days (80's) with very high humidity. The house always felt hot, really it was just the humidity was high due to the A/C unit short cycling. Now in ANY conditions the house is a perfect temperature AND humidity.

No more blowing air, it used to be so obvious when the A/C was on with the air blasting out of the ducts, now it just cruises along without a big rush of air even in 110 degree temps.

My electricity bills in the summer have been about $100 a month lower. No it wouldn't pay for the difference between this unit and the cheapest, but it helps.

DC is the future IMO.

 

[mrpizza]

I have the trane XV fully variable speed system. It's awesome, runs a lot to maintain comfort but the bills are quite low from the utility co.

 

[DHCrocks]

I have the Maytag IQ drive (Nordyne inverter compressor) and I love it. it's so quiet compared to the old single stage Rheem. I would never go back to a single stage. it so much more comfortable to just have the AC chugging along at a slow speed to maintain the temp rather then having it come on quickly cool down and shut off. The house stays at a more constant temp without the temp fluctuations. It also cut my electricity usage I think it went down about between 200-400 khw a month.

Even if your payback for the upgrade of a variable speed doesn't make sense, the added comfort and quietness is well worth the added cost.

 

[Notgrownup]

My Goodman system is 15 years old, I asked my AC guy this year if it was worth replacing, he said why? He would run it until it dies and cost too much to fix...has never leaked a ounce...
He said unless I wanted a really quiet system I could save money and stick with single stage, Dual stage might be good enough but the variable speed units are the quietest one but cost more to repair when they go south.

 

[dat2109]

@alexb2000 If you are saving $100 a month in the summer, even only counting those 3 summer months that's $3000 over 10 years. What was the markup?

So far I've had 3 local guys come do quotes and they were all pushing me into Caddilac single stage systems instead of anything 2 stage.

 

[yeldogt]

Understand, a two stage furnace is not the same as a two stage AC compressor. Gets confusing today because there are so many different models.

In cold climates the ability to have staged heat allows the heater to better match the load depending on outside temp. Years ago it was only two different outputs with corresponding two fan speeds to match that output. It was mostly limited by the gas valves available -- manufactures came out with 5 step valves and then 10 .. until they finally came out with infinite variable for both the gas valve and blower fans. The same basic idea is occurring on the AC/HP side with the compressor. It applies the same way for those who need mostly AC.

The degree of improvement going with the more advanced equipment is all dependent on the house and climate .. Bosch just came out with an 80% gas furnace that will work with a fully variable speed AC compressor. It's for areas where AC is primary and the small saving going to a more complex and costly condensing furnace would not provide payback. I only point that out as there are so many possibilities that are designed for particular parts of the country.

The issue the OP has is w/o replacing the furnace -- he can't get the benefits from a more advanced AC system. Many of the system will run w/o the factory supplied control thermostat -- but they do so using an internal algorithm. IE: they run for so much time on low and if the thermostat is not satisfied they move to high. I don't see the point -- why pay for the equipment and not use it .....the higher end full modulating equipment needs the factory control .... the two systems I'm looking at currently for my build (Carrier and Trane) require the manufacturer communicating thermostat.

In humid climates the ability to lower the fan speed and still monitor the coil for freeze protection allows the units to pull out the humidity w/o overcooling the house. Even with the scroll compressor two speed not being a big drop in capacity -- it allows for longer run times ... this pulls more moisture from the house. We have had an incredibly wet year on the east coast --- my 5 stage has been running on stage 1 most of the time to keep the house humidity down.

 

[jimindm]

We have an old two story house that started out as a gravity furnace that some one added a blower to. When we bought it we put in an HVAC system. 80% i think and nothing fancy. Of coarse we used much of the existing duct work, due to cost and the upstairs was significantly different than the main floor, temperature wise.

We added on a two story addition. Tried to incorporate some cold air returns up stairs. The addition includes a full basement under it. Went up a size or two of the system, but still had temperature fluctuations between floors. I think that was a no frills units, but it was a 90% or so.

Twelve years later the outside unit gives up. The POCO rebates were just to good to pass up on getting a furnace also. Almost every contractor recommended multi stage, variable speed units.

I can say that the new one is very quiet, and like others have said the house is just more comfortable. There is still a little difference in temperature from second story and the basement.

My wife is a farm girl moved to the city. She can not take open windows and the noise of city life that goes with it. Our heat is turn off in the spring, just a few days before the ac is switched on. Same way in the fall.

I can not help you on the cost savings to operate it, she pays the bill. Seat of the pants though it is much more comfortable in our home.

Funny some one mentioned a tstat. We are on our third one in two years. If I had to give any advise I would say go with a contractor that does many of them. Now ours is two years old and it may have been newer systems for the company. It just seemed like he was sort of at a loss when he was fine tuning it after install. He came back several times and the last time had some kind of factory teck guy on the phone with him. I would guess two years has made a difference in that.

 

[yeldogt]

@alexb2000 If you are saving $100 a month in the summer, even only counting those 3 summer months that's $3000 over 10 years. What was the markup?

So far I've had 3 local guys come do quotes and they were all pushing me into Caddilac single stage systems instead of anything 2 stage.

Ask them to price a system you want? -- also, ask them how many multistage systems do they install. Some guys have little experience with the equipment -- others do them day in an day out. I found many discounting the better equipment w/o any real reason other than the normal "this is they way we always do it" "you don't need it" "too costly to fix"

 

[bdbecker]

We upgraded our system a few years ago and saw a small cost savings, but a huge improvement in comfort. I also like how quiet it is. No regrets at all and would totally do it again.

 

[gpiggaz]

We just went through this same decision in Tucson when our 20 year old Heat Pump died. We could have replaced the compressor but decided after 20 years to replace the whole furnace. The choices were conventional, 2 speed or variable speed. The cost of each was higher than I expected, but we ended up going with the variable speed, mostly not to save money but to make it quieter- it's almost silent running now. The cost savings is about $75/month so far while using AC and I expect the cost savings to pay for itself about the same time the unit dies, so no real cost saving expected. We ended up using the local Costco contractor- price was fair- and the 10% rebate helps a little to offset the additional costs. Biggest issue we had was that it was summer and the system was dead, Costco got a guy to our house on a Sunday and the install was on Tue- could have been Monday had I been able to get the guy there a little earlier in the day Sunday- he got there at 3:00pm and the install started at 8:00am Tue. Couldn't be happier that I was when the temperature inside the house started coming down from the 109! Lost a few candles, but nothing else seemed damaged.

 

[jshillin]

The coil in one of my 10 year old Heat pump's(downstairs) had a bad leak early this year. I went through, got quotes from several companies to repair and replace.

In the end I went with an 18 SEER Inverter Setup. I looked at the 20 SEER, but it had the same HSPF, so it made no sense to upgrade. My house is so much more comfortable since making this change. No regrets at all. It heats and cools more evenly and it runs as low as 25% more often then I expected. I'm hoping my old unit for the upstairs makes it a few more years, but I'll replace it with the same setup when it does go up.

 

[slimcake]

Carrier Greenspeed system in my new house. LOVE IT!!! For all the reasons mentioned. 25 below zero out side and every spot in the house is the same temp. Furnace doesn't shut off but it runs so slow to keep the air moving and the whole house is so comfortable. Same with the AC. Would def do it again!!

 

[dat2109]

Thanks for the responses everyone.

I'm still working on getting quotes fine-tuned here, I've bought a number of units over the last decade or two and have generally had great luck. One house in the south had a 2 stage 96% gas furnace paired with an older single stage a/c. The furnace was using its own 'algorithm' control for the stages - dumb thermostat that simply called for heat.

I want to say that the heating bill was $100 (or more) less per month compared to an 80% single stage. That cooling on the other hand was not great - the furnace was programmed to single blower speed when cooling.

 

[Trey T]

the Bosch variable speed inverter system is worth it. It's about the same price as a goodman 16seer system (heat pump) - yeah stupid cheap!!!

Some multi-stage unit can cost twice as much as the Bosch. yeah it's really weird and I would get it.

 

[yeldogt]

Carrier Greenspeed system in my new house. LOVE IT!!! For all the reasons mentioned. 25 below zero out side and every spot in the house is the same temp. Furnace doesn't shut off but it runs so slow to keep the air moving and the whole house is so comfortable. Same with the AC. Would def do it again!!

I'm assuming you are using the matching infinity gas furnace ? How cold are you running the Greenspeed ? I asked because when I was looking the only complaint I had with the Greenspeed was the inverter noise when operating in HP mode at very low temps. That's why I went with the 5 speed Infinity .... all the units are the nosiest when running on high at the lowest outdoor temps .. but, the 5 speed was still almost silent and no high pitched inverter noise ... evidently they don't all have the issue.

 

[slimcake]

I have yet to use the heat pump side of the green speed system. I have natural gas and it is cheap so I have been using the Infinity gas furnace with the modulating fan and gas valve. Like I said it is not even audible. Awesome setup!!

 

[yeldogt]

I have yet to use the heat pump side of the green speed system. I have natural gas and it is cheap so I have been using the Infinity gas furnace with the modulating fan and gas valve. Like I said it is not even audible. Awesome setup!!

That's what I figured -- the cost to add the HP was not enough to not do it .. and I'm glad I did. Since the system is zoned I use to to balance out the whole house .. and it kept 1/2 the house warm when I was remodeling and part of the radiant was down.

 

[alexb2000]

@alexb2000 If you are saving $100 a month in the summer, even only counting those 3 summer months that's $3000 over 10 years. What was the markup?

So far I've had 3 local guys come do quotes and they were all pushing me into Caddilac single stage systems instead of anything 2 stage.

I am suggesting a DC or completely variable system vs. 2 stage, or 1 stage. The advantage is the unit can be any size you need it to be. My house specs. at a 4 ton, I bought a 5 ton. On a day when I need only 1 ton I have it, on a day with 30 people in the house for a party I have extra cooling capacity that I don't pay for everyday and no short cycling issues. 2 stage is a compromise IMO. Everyone will tell you the DC inverter systems are expensive to repair and I'm sure they are. However, the warranties are not that much ~$800 in my case for 10 years parts and labor. It probably cost me $8K more (including warranty) for this system than the cheapest single stage on the market.

It hard to explain how much nicer these systems are until you have one. Right now we have 90 degree days with 90% humidity. My house is a steady 55% humidity at 72 degrees, that is very hard to hold with a traditional HVAC unit while still having the capacity for the 110 degree days.

I have no idea why the HVAC guys push the low SEER single stages, maybe they can chime in.

 

[yeldogt]

I am suggesting a DC or completely variable system vs. 2 stage, or 1 stage. The advantage is the unit can be any size you need it to be. My house specs. at a 4 ton, I bought a 5 ton. On a day when I need only 1 ton I have it, on a day with 30 people in the house for a party I have extra cooling capacity that I don't pay for everyday and no short cycling issues. 2 stage is a compromise IMO. Everyone will tell you the DC inverter systems are expensive to repair and I'm sure they are. However, the warranties are not that much ~$800 in my case for 10 years parts and labor. It probably cost me $8K more (including warranty) for this system than the cheapest single stage on the market.

It hard to explain how much nicer these systems are until you have one. Right now we have 90 degree days with 90% humidity. My house is a steady 55% humidity at 72 degrees, that is very hard to hold with a traditional HVAC unit while still having the capacity for the 110 degree days.

I have no idea why the HVAC guys push the low SEER single stages, maybe they can chime in.

While oversizing is dangerous -- if you typically have that many people in a house .. you really many not be oversizing. Everything should be load based because even the best units can only drop down to 25% .. some are only 40%. This is what you have to look at what you are buying.

The units are not running at peak efficiencies throughout the range -- they like 70-80 capacity for peak. They still are more efficient vs running a single. A 5ton is still giving 2t at 40% and that is often too much.

The guys push the single stuff -- because that is what they know .. and they can switch them out and make a profit. There is a whole learning curve with he more complex equipment -- and often training. I was not sure about the Carrier 5 speed (and I'm not pushing that model) -- but the one installer had one at his house and the carrier engineer from the regional rep did as well. They both told me it was the perfect fit and also not the most expensive. They both also understood the benefits of zoning in an old house -- and the new multi speed equipment is tailor-made for zoning -- often very easy add on module. Zoning can make an older house with bad undersized ductwork much more comfortable.

 

[bobbyjean]

I'm needing to have my A/C replaced because its 14 years old and started leaking freon. The furnace is the same age and as far as I can tell working okay other than some noise that might just be the install.

My question is about upgrading from a basic single stage to multi-stage cooling and variable blowers. Is it just going to be more expensive for little return or a whole house comfort improvement?

Currently, the A/C is single stage single blower speed r-22.
The furnace is an 80% single stage natural gas.

I've had a 95% furnace before and noticed the savings over an 80%.
I don't think I've ever had a/c better than 13 seer, if even that.

To just replace my a/c I would be going with a 14 seer single stage unit.
The next step up in efficiency seems to require a multi-speed or variable (communicating?) blower fan and that's part of the furnace. I don't know if they make retrofit kits or something else to keep the furnace going. Otherwise, it seems I am going to need to upgrade the furnace too.
The final step up would be variable blower speed with a two stage compressor.

your call...you get what you pay for...new system will cost big but will be very efficent....i'm cheap so my answer would be no to the big upfront/big number on parts and service...burn wood not dollars

 

[Jackfre]

Heating and cooling loads calls are based upon design conditions. That is the hottest and the coldest days you will see. When you consider that you are at design condition around 1% of the time your typical system is dramatically oversized. You then have a contractor come in and he looks at the load calc and says a 75k furnace will do it, but he will likely put in a 100 and tell you that you have plenty of capacity. You are oversized by design and then further oversized by selection. Variable speed modulating equipment softens that issue and greatly contributes to your comfort. Go for it, you will be happy you did.

 

[yeldogt]

Heating and cooling loads calls are based upon design conditions. That is the hottest and the coldest days you will see. When you consider that you are at design condition around 1% of the time your typical system is dramatically oversized. You then have a contractor come in and he looks at the load calc and says a 75k furnace will do it, but he will likely put in a 100 and tell you that you have plenty of capacity. You are oversized by design and then further oversized by selection. Variable speed modulating equipment softens that issue and greatly contributes to your comfort. Go for it, you will be happy you did.

Very difficult to get people to buy into the concept of just enough ... even when the design is a little short I err on the side of smaller .... have never had a problem -- because, by design the formulas have a fudge factor.

When I did my first full radiant project back in the early 90's getting the load calculation information was very difficult. I lucked out when the people who were manufacturers reps for the newly introduced Buderus boilers helped me out .... they were commercial people and doing full room by room calculations was more common. My system had to be designed for DHW .. not the house.

Homeowners don't want to believe that in most cases very little thought went into sizing and laying out the HVAC -- cost is often the first priority. No one buys a house based on the HVAC ... even builders of expensive homes pay little attention to it. It's cost driven ... another problems is that until very recently manufacturers only made a few sizes (big and bigger) ... as homes became more efficient .. the sizes stayed the same .. adding to the oversized equipment problem. Many homes need under 50k and the smallest furnace will be 75k for gas and 120k for oil. The original system in many homes was based on some general rule and price -- the next guy just matches what is in the house. Unless you live in a house with a really good system -- good enough is typical and what people expect. No calculations are ever done.

While I have built a couple complete new homes -- most of my projects are retrofits/rebuilds and expansions of existing structures .. often odd. I have done a firehouse -- small factory building and I'm currently converting a church into my home. All of these require even more calculation and attention to detail when designing and laying out the HVAC. The heat and cooling loss can be all over the place depending on if you want to expose a stone wall -- or if it has high ceilings and large windows like my church project. Toss in that very few know how to factor in the use of foam insulation. Foam really can be a problem -- it's that good --- people doing the calculations are afraid to install the small equipment

That's why I like zoning so much -- since most houses are never fully occupied the ability to direct the capacity to where it's needed allows for even smaller equipment. If the design temp for an area is 0 .. and it only gets to zero once every 5 years for two days. Do you design to keep the dwelling at 72 for that temp? Same with AC .. I had a guy do the design temp at 70 .. and 105. That has happened maybe once in my lifetime in my area -- and for a couple hours. And with the proper humidity control the smaller equipment can produce --- I find that 72 gets too cold for many with low humidity.

The only problem I am seeing is that people are oversizing the VS equipment -- with the idea of excess capacity .. for what? It defeats the reason for the equipment