Two Systems into One

[jeffr_ca]

Greetings,

We have a 2600 sq/ft house (1500 on main, 1100 on upper) currently serviced with two separate furnaces. One of the two units has a 2 ton A/C to heat & cool the upper floor. No A/C on the main floor via the second system. The main floor ductwork is sized proportionally larger as compared to the upper floor ductwork.

We are evaluating options for replacement of the system with High Efficiency units. The recommendations range in order of the highest cost to lowest as follows:

Option 1: Replace two furnaces with a single unit, sized for the entire house, with new condenser and zone control system. Changes required to merge ductwork are somewhat challenging but not extremely difficult. Contractor has installed similar systems with reportedly good success. The downside is total cost about 40% higher than lowest cost option.

Option 2: Replace two furnaces with two new furnaces and one condenser sized for upper floor only. Essentially replace exactly the same configuration with the downside being that we do not gain A/C on the main floor which is desired (temperature variance between conditioned upper floor and unconditioned main floor is significant). Control over the zones is excellent with the two separate furnaces and thermostats, but A/C only on upper floor.

Option 3: Replace two furnaces with one new furnace and one condenser sized for entire house. No zone control, but consider manual dampers in trunks to adjust for seasonal requirements (more flow to upper during A/C season and more flow to main for Heating season). This is the lowest cost option, but only about 10% less than Option 2 and would not provide any automated zone control.

All three contractors are experienced and highly regarded, but have different opinions on the solution.

Our concerns are with Option 3 providing much by way of zoning efficiencies, but we expect that the fan running 24/7 on low speed will maintain even temperatures throughout the house.

Our concern with Option 2 is not gaining of A/C on the main floor, unless there exists a condenser that may be able to service two independent coils. If such a solution were available then this scenario would be a good cost/benefit solution. Installing separate condensers for each furnace-A/C unit would be impractical for space limitations and would become as costly as Option 1, but would provide absolutely independent and fully programmable zones serviced by their own system and ductwork.

Our concern with Option 1 is the overall cost and the actual benefit of utilizing zoning to save costs during heating season by lowering the temperature of the unused zones at the appropriate hours. Can the extra cost ever pay for itself in dollars or in level of comfort assuming that Option 3 can circulate and maintain even temperatures throughout the building?

I'm interested in comments or concerns with the recommendations.

Thanks!

[jrock52766]

option 3 will not give you the even temperatures through the house that you desire. no if, and's or but's about it.

option 1 is your best bet since your not satisfied with the current set up you have(rules out option 2)

A zone system, when done correctly, will make you think you had the second a/c system installed on that downstairs unit.

[21degrees]

Zoning get expensive and problematic after years of service, variable speed gets noisier. Top floor will be hot and bottom floor will be cooler. I would go for 2 furnaces and 1 air conditioner with variable speed blowers and run fan 24/7 if installed right they are quieter. Lower cfms means lest noise as long as your duct work is sized properly.

[jeffr_ca]

Thanks Jrock...

For option 1: I know you said "no ifs, ands or butts"....but, is there no amount of airflow (ie. even on high) or balancing of dampers that could equalize temperature throughout? Or is it just not worth pursuing? Funny, contractor for Option 2 stated you'll never be happy merging into a single unit....and wouldn't recommend doing it.

For option 2, is there any condenser that you are aware that can service two coils, ie. two compressors in a single frame or any sort of pressure valves that can switch between one or the other coil on low stage and serve both on high stage? I'm assuming two coils in series couldn't work as the non-called coil wouldn't be seeing any airflow....

For option 3, looking like where we have to go (sigh with $$$). Do they really work that well...you sound very certain. What should I be watching for to ensure that the system is properly installed? i.e. should the returns be dampered as well?

[jrock52766]

jeff,

even if the the temperature in a two story house could be kept even with one system using manual dampers they would still have to be adjusted twice a year for heating season and cooling season. So you would be paying someone to do it or crawling around your attic and hoping you got it right.

The only single systems i have seen with 2 cooling banks(2 compressors and 2 coils) are in commerical package units.

The zoning systems do a great job as long as they are installed correctly and the duct sizing is correct. A key point is to pay attn. to the warrenty on the dampers that are used as they are the primary component to fail in zone systems. Several zone brands have 5 yr zone board warrenties but on 1 year on the dampers. I do know that Aprilaire has 5 year warrenties on all the products they make. Heres a link to the website that will give you more info http://www.aprilaire.com/

[jeffr_ca]

Zoning get expensive and problematic after years of service, variable speed gets noisier. Top floor will be hot and bottom floor will be cooler. I would go for 2 furnaces and 1 air conditioner with variable speed blowers and run fan 24/7 if installed right they are quieter. Lower cfms means lest noise as long as your duct work is sized properly.

Thanks 21Deg....

Based on your Location information, you share the climate that we are dealing with.....-40c in winter and occasional +40c in summer.

I'm a "fan" of running the blowers 24/7 for circulation and temperature. But is there a practical method that we can mix the airflow between the two floors to provide sufficient cooling in summer from the single A/C unit?

As it works now, the A/C unit for the upper floor cools appropriately. But the temperature of the main floor can be 10+ degrees higher on hot summer days. This doesn't seem efficient to me, where part of the house is 85 deg with high humidity and the other is 72 deg/low humidity. Somehow, I'd like to gain A/C for the entire house, but with reasonably consistent temps.

These days, there are so many 2500 to 3500+ sq/ft houses being constructed....how do they equalize temperature with the single furnace-A/C installations? Or don't they?

[jeffr_ca]

Duplicate post....sorry.

[thehumid1]

Option 1 sucks, 2 systems are always better than 1. 1 of 1 systems breaks your f'd. 1 of 2 breaks --sucks but you can get by until the other is fixed. U do the math.

[jrock52766]

in respone to that last question you asked, jeff, i know in atlanta it is code to have a zone system on any two story house with one hvac system in new construction. That is what they are doing there and heat and hunidity are a major concern in that city, and the zone systems are keeping the houses comfortable last i heard.

[jeffr_ca]

jeff,

even if the the temperature in a two story house could be kept even with one system using manual dampers they would still have to be adjusted twice a year for heating season and cooling season. So you would be paying someone to do it or crawling around your attic and hoping you got it right.

The only single systems i have seen with 2 cooling banks(2 compressors and 2 coils) are in commerical package units.

The zoning systems do a great job as long as they are installed correctly and the duct sizing is correct. A key point is to pay attn. to the warrenty on the dampers that are used as they are the primary component to fail in zone systems. Several zone brands have 5 yr zone board warrenties but on 1 year on the dampers. I do know that Aprilaire has 5 year warrenties on all the products they make. Heres a link to the website that will give you more info http://www.aprilaire.com/

Jrock...

We actually have a full basement where the furnace(s) are installed, so access is easy. We anticipate some experimentation to determine a "winter" and "summer" position for manual dampers, but re-setting them each season would be easy.

Thank you for the link on the Aprilaire products. All the systems offered so far are completely Lennox equipment (including the zone control). Any concerns there? I will confirm warranty coverage on the dampers, etc. (furnace and A/C are 10 years parts/labour). I'm assuming clean air/filters could affect life of damper mechanics.

Please confirm my understanding in that the zone system would behave as though there were two furnaces-A/C units depending on the call from the two thermostats. Zone "A" makes a call - Zone "B" dampers close. Zone "B" makes a call - Zone "A" dampers close.

If both zones make a simultaneous call, all dampers would be opened.

If both thermostats have "fan" enabled, all dampers would be opened and we would gain full circulation throughout the house through single blower (that's good, as it would help equalize temperatures).

[thehumid1]

Again stay with 2 independent systems. Do not convert to one and zone it.

[jeffr_ca]

Again stay with 2 independent systems. Do not convert to one and zone it.

Hi Humid....

Perhaps it's more common to have two systems than I've experienced.

I understand what you're saying about redundancy in having two systems regarding failures, but most houses don't have any type of backup system even in the cold climate where we live. We have to be somewhat dependent on the reliability of the systems we have installed. There are 24 hour emergency services available.....so long as someone is home to know that there's an emergency.

Is it common to have two A/C condensers (one for each furnace/coil)? Adding the second A/C system would give us the ultimate in zone control and redundancy, but it seems excessive for the 8 weeks of a year that we may require A/C. This would take the cost to about equal that of the zoned system.

[beenthere]

2 heating cooling systems for one house is not unusual.

So option 4 is the best.
1 funace and A/C for the second floor.
1 furnace and A/C for the first floor.

[adrianf]

Done CORRECTLY the zoning is the only way to achieve control of up and downstairs. You can zone with a damper system or you can zone with multiple units. The issues of noise and reliabilty all hinge on the quality of the product and contractor chosen. One thing if you choose a damper system is you should use a dual capacity outdoor unit(A/C) Running the indoor fan(s) 24/7 with raise the humidity in your home during the cooling season. So what do you have the appetite for and/or you willing to compromise comfort and control for the up front savings. If you are concerned about repair/ownership cost buy a FACTORY extended warranty that will cover the complete system.(equipment and zoning) The decision making matrix will consist of several items but only you can bring your priorities to the forefront. First cost, level of control, warranty, energy savings, brand, reputation, and ..........................................

We often condenm that which we do not understand.

[beenthere]

Not sure if anyone straight out condemned zoning.

But since the duct system is already set up for 2 systems.
Zoning with one 2 stage heat, 2 stage cooling system isn't really going to be anymore cost effective upfront.

2 systems may allow closer sizing.

Either method done right will work. Just more chance of it not being right by zoning.

[jrock52766]

quick question for the OP, what is your main reson for looking into replacing both systems now? A complete system for both floors is the ideal set up to have but would more than likely also cost more. My suggestion is that if the upstairs unit is working properly then look into replacing the downstairs system only and having the a/c added to it. This way you will have 2 complete systems (upstairs will be older) and you can have the other system replaced when you are financially able to. You dont have to do both systems at the same time. Yes it would be nice to do both at the same time but we cant always just get everything at once. I have had several customers replace one complete system, pay it off in a year and then do the other. Nothing wrong with that.

[jeffr_ca]

quick question for the OP, what is your main reson for looking into replacing both systems now? A complete system for both floors is the ideal set up to have but would more than likely also cost more. My suggestion is that if the upstairs unit is working properly then look into replacing the downstairs system only and having the a/c added to it. This way you will have 2 complete systems (upstairs will be older) and you can have the other system replaced when you are financially able to. You dont have to do both systems at the same time. Yes it would be nice to do both at the same time but we cant always just get everything at once. I have had several customers replace one complete system, pay it off in a year and then do the other. Nothing wrong with that.

Thanks Jrock....

That's a good point that I guess we had dismissed because we were on the track of merging the ductwork. The "do it in one shot" approach.

There are a variety of reasons to proceed with replacement (i.e. gov. grants, improved efficiency, lower operating costs, moving a condenser that's in the way of new deck, etc. etc.). It's not that we're not financially able to replace both right now, it's more a matter of selecting the right combination of solution/comfort/value.

Having 2 condensers outdoors consumes quite a lot of space (things are a bit crowded around the house already)....but it sounds like the ultimate solution.

I also need to ask the contractors to equalize their proposals a bit. For example the Zone Controlled solution includes all premium options XC15 vs XC13. HC15 vs. common 5" filter pack. G71 vs. G60, etc. Cased coil vs. custom. Perhaps only a couple hundred dollars per tweak, but when added up, they change the picture.

Lot's of variables and I'm sure if I called a 4th contractor I would get another option. We have time on our side, so I can evaluate further solutions and even visit existing installations.

The consensus seems to be that a single replacement unit will not maintain comfort without automated zoning control. When comparing the cost of that, it may be more versatile to simply install two fully independent furnaces and A/C units.

I appreciate everyone's comments and suggestions. Thank you.

[catmanacman]

with 2 systems you can better manage you utility usage . using digital programmable t stats I would not downgrade to 1 system