Any HVAC experts out there?

[Scuba Steve]

One of our two heat pumps is more or less dead - there is a big leak somewhere and the compressor smells burnt. The system in general was installed wrong in numerous ways and replacement is looking like a good option. A load calculation and verified a 3 ton system. Any thoughts on the three system quotes I have been given so far?

House is in Charleston, SC. 3,300 sq ft, 1 floor, no shade from trees, built in 1959 and this is one of two systems split evenly between the total square footage.

$8435
17 SEER Trane / 2 stage heat pump condensor (4TWR7036A1000A)
Variable speed air handler (TAM7A0C36H31SB)

$6820
15 SEER Trane heat pump (4TWR5036G1000A)
Single speed air handler (GAM5A0C42M31SA)

$5585
14 SEER Trane heat pump (4TWB4036G1000A)
Single speed air handler (GAM2A0C36M31SA)

[sammyg2]

I wouldn't exactly call myself an HVAC expert, but I did finally get my programmable thermostat to work.


(With my son's help).

[peppy]

Not an expert.

I really like the variable speed air handler I think it ads to the comfort with the heat pumps.

As for the SEER I don't see the big gain for an older home for the added cost.

I would want a lower SEER with a variable speed air handler.

[cabmandone]

My first thought is, I REALLY need to get back into HVAC

Now, I'd do the 2 stage H.P with the variable speed indoor air handler. Better yet get a 98% variable speed furnace and go dual fuel. Some power companies offer rebates for dual fuel and for high efficiency heat pumps. I like gas forced air if you have the option simply because if/when the electric resistance heat kicks in, you won't like it. BUT, you don't have the heating needs like we do up here in NW Ohio either. Assuming they put in backup resistance heat they should stage it so that when the second stage heat pump kicks in, if it won't keep up, 10 kw of electric will kick in to supplement your heat pump.

Make sure they are installing the system that best fits what your duct design is, that is if you're not replacing the duct system with the equipment. The two stage variable speed systems need proper duct design to reach full energy efficiency potential.

[calimedeiros]

I'm a hvac teck and to my experiences some people live the variable speed stuff sure it's more efficient and all that but when it comes time to replace some of these parts your gonna pay big
some of these motors and extra gadgets they throw in these things are very expensive to replace When they break

[gshase]

Here is what I know....If your house is Super insulated and the unit will be off most of the time; Then a 17 SEER is not going to save you much.(The saving is only when it is running) Then go to a 15 SEER. On the other hand if your house lacks insulation and the unit will run 60% of the time then get the Highest Seer you can afford.

[BK911]

How many rooms? Which rooms? When one of my units fail, I am going with a multiple cassette ductless split system. One variable speed compressor feeds several indoor units. Each zone has its own stat.

[Scuba Steve]

The house was built in 1959 and it is a single story ranch/modern. Gas is available at the house but I would need to upsize the line from the meter in order to add any more appliances. Typical heating is an day like today where the high is in the 50s, low in the 30s. Cooling is from march-october.

The area this unit covers is the den (my office), formal living, kitchen, dining room, entry hall, one bedroom and one bath. This is generally the northwest section of the house. The ceiling has 6" of blown in insulation except for the den which only has R6 in places where the drywall is covered, the floor is concrete in some areas/uninsulated crawlspace in others. On the plus side the place is sealed up pretty well.

Backup heating is electric. Ducting is actually good if not oversized. There are 12x12, 20x20 and 20x25 intakes. I'm leaning towards the middle and high systems because for some reason this system tends to run more than the other. I just have no real idea what the effective difference between 15 and 17 SEER and the variable speed air handler would be or if I would ever reach the break even point.

[EarlyPorsche]

If you cool that much of the year how about going to a dedicated AC instead of heat pump? Is that an option?

[911dean]

I was a Tech for 20+ years. I like the Variable speed option with a lower SEER than 17. I'd personally go with a 14. As stated in another reply, the variable speed stuff can get expensive to repair, but there's very good warranty's available and I didn't do a whole lot of repair to it anyways. Also, I never replaced the actual motor, just the module.

[Scuba Steve]

Originally Posted by EarlyPorsche

If you cool that much of the year how about going to a dedicated AC instead of heat pump? Is that an option?

If I did that I would need a dedicated heat source, and I'm in a tight spot there because the gas line coming from the meter would need to be upgraded (and a longer run to reach the area) to add one. Things get cold enough so that a straight electric heater would be expensive to operate.

I miss the super warm air that the gas furnace in our old place put out but it's hard to see how it would be cost effective.

Dehumidification is another big issue in this part of the world. Would a variable speed air handler be able to do that more effectively than a single speed one? I added a dedicated dehumidifier to our system because humidity was a problem but it tends to run a lot.

[billybek]

Contact your gas supplier and see if they have a construction side that would upgrade and move the gas line and get a quote. You could see if a local plumbing/gasfitting company would provide a quote for comparison.
I am not familiar with the Trane two stage compressors for this product line and up here we rely on gas heat as there is very little heat available outdoors when it is minus 30 degrees outside!
I am just looking to replace my high efficiency furnace. 15 year old Trane that has developed a bit of a control board glitch. The cost of the board replacement kit is just under half the cost of a new furnace plus the fact that I would need to retrofit several components on the furnace for the repair.
My next one will have a variable speed blower motor on it but I may stay away from variable fire on the gas side.
I wouldn't be afraid of the technology and would install the most efficient system that you can afford at the comfort level that you desire. Check all the manufacturers product but I would go with the one that offers excellent local service. Ask for references and see if you can look at their installed work.
A few years ago people were afraid of buying a car that didn't have a carburetor and ignition with points!

[cabmandone]

Originally Posted by gshase

Here is what I know....If your house is Super insulated and the unit will be off most of the time; Then a 17 SEER is not going to save you much.(The saving is only when it is running) Then go to a 15 SEER. On the other hand if your house lacks insulation and the unit will run 60% of the time then get the Highest Seer you can afford.

If his load is split in half as it appears he said it was he's got 6 ton in a 3300 s.f home. I'm guessing a lot of windows and possibly only minimally insulated attic and walls.

[cabmandone]

Originally Posted by Scuba Steve

The house was built in 1959 and it is a single story ranch/modern. Gas is available at the house but I would need to upsize the line from the meter in order to add any more appliances. Typical heating is an day like today where the high is in the 50s, low in the 30s. Cooling is from march-october.

The area this unit covers is the den (my office), formal living, kitchen, dining room, entry hall, one bedroom and one bath. This is generally the northwest section of the house. The ceiling has 6" of blown in insulation except for the den which only has R6 in places where the drywall is covered, the floor is concrete in some areas/uninsulated crawlspace in others. On the plus side the place is sealed up pretty well.

Backup heating is electric. Ducting is actually good if not oversized. There are 12x12, 20x20 and 20x25 intakes. I'm leaning towards the middle and high systems because for some reason this system tends to run more than the other. I just have no real idea what the effective difference between 15 and 17 SEER and the variable speed air handler would be or if I would ever reach the break even point.

If you're not going to have the duct designed to fit the 17 SEER with the variable speed air handler, don't buy that system. As I wrote earlier, you need the duct designed to fit that system. The old method of duct design isn't adequate for that system you won't obtain the rated efficiency without the proper duct design.

[cabmandone]

Originally Posted by billybek

Contact your gas supplier and see if they have a construction side that would upgrade and move the gas line and get a quote. You could see if a local plumbing/gasfitting company would provide a quote for comparison.
I am not familiar with the Trane two stage compressors for this product line and up here we rely on gas heat as there is very little heat available outdoors when it is minus 30 degrees outside!
I am just looking to replace my high efficiency furnace. 15 year old Trane that has developed a bit of a control board glitch. The cost of the board replacement kit is just under half the cost of a new furnace plus the fact that I would need to retrofit several components on the furnace for the repair.
My next one will have a variable speed blower motor on it but I may stay away from variable fire on the gas side.
I wouldn't be afraid of the technology and would install the most efficient system that you can afford at the comfort level that you desire. Check all the manufacturers product but I would go with the one that offers excellent local service. Ask for references and see if you can look at their installed work.
A few years ago people were afraid of buying a car that didn't have a carburetor and ignition with points!

If I was in your area I'd absolutely consider a furnace with High/Low firing rates. Don't let the technology scare you. I installed Carrier and put in several of these and honestly don't recall having problems with them. When my furnace goes in my house I'm DEFINITELY going with a 2 stage gas furnace with variable speed blower.

[Scuba Steve]

Originally Posted by cabmando

If you're not going to have the duct designed to fit the 17 SEER with the variable speed air handler, don't buy that system. As I wrote earlier, you need the duct designed to fit that system. The old method of duct design isn't adequate for that system you won't obtain the rated efficiency without the proper duct design.

I'm genuinely curious, in what way are they different? The current ducts are unusual to me. They were put in about 10 years ago and there are three returns (20x20, 20x25 and 12x12). Not sure how many registers there are... typically 2 per room and they're 4x12. Towards the middle-late life of this system we will need to re-roof and the actual shape of the roof might end up changing a lot (long story, house was added on to twice and now it's a terrible design). At that time I had planned on addressing ductwork since what's in there now is in good condition.

I spoke with someone earlier and a load calculation will be done this afternoon. The attic has 6" of blown in cellulose insulation, there are 150 sq ft of double paned vinyl windows in this part of the house, a NE-facing front door and I forget the total amount of exterior walls but they face northeast/northwest + a couple of walls adjacent to the garage. They are insulated to R-11.

I will call the gas guy who ran the line for our cooktop this summer to get his thoughts about whether we can handle a furnace. The current system felt oversized for cooling / not sure about heating. I miss the simplicity and hot air from gas

[cabmandone]

Originally Posted by Scuba Steve

I'm genuinely curious, in what way are they different? The current ducts are unusual to me. They were put in about 10 years ago and there are three returns (20x20, 20x25 and 12x12). Not sure how many registers there are... typically 2 per room and they're 4x12. Towards the middle-late life of this system we will need to re-roof and the actual shape of the roof might end up changing a lot (long story, house was added on to twice and now it's a terrible design). At that time I had planned on addressing ductwork since what's in there now is in good condition.

I spoke with someone earlier and a load calculation will be done this afternoon. The attic has 6" of blown in cellulose insulation, there are 150 sq ft of double paned vinyl windows in this part of the house, a NE-facing front door and I forget the total amount of exterior walls but they face northeast/northwest + a couple of walls adjacent to the garage. They are insulated to R-11.

I will call the gas guy who ran the line for our cooktop this summer to get his thoughts about whether we can handle a furnace. The current system felt oversized for cooling / not sure about heating. I miss the simplicity and hot air from gas

The design of the entire duct system is differnt. IIRC the static pressures used to calculate the duct system are different than for standard fixed speed systems. Your heat pumps are designed more for the heat load (which is why you have a problem with dehumidifying) but you're supposed to balance the heat and cool loads and at a certain outdoor ambient bring in either electric resistance heat to supplement or automatically switch to your gas system if the outdoor reaches the designed balance point. Something else, your return air is supposed to be split between high and low meaning some up toward the ceiling and some down at the floor. An old rule of thumb to figure out how much air you're moving, 1 6" round supply is equal to 100 cfm. A 7" is 150 cfm, a 8" is 200 cfm. Total CFM is 450 per ton on a heat pump 3 ton @450 is 1350 total CFM.

If you rely on your heating load alone to determine the size of the system and are calculating it without bringing in auxiliary heat you could oversize the unit for the cooling load which will adversely effect your dehumidifying capability because the cycle time will decrease meaning your house will get to the desired temperature before you have sufficiently removed humidity. I designed an all electric system a long time ago for a small duplex where we based the size on the cooling load and staged in electric resistance heat based on the outdoor temp. We did that to enable the system to properly remove humidity in the summer.

It would seem in your area that the cooling load would be greater than the heating load but for the size of your house, (mind you the following is written without me seeing your home) it seems you're over sized on the air conditioning side of things simply because you mentioned the problem of insufficient dehumidifying.

I hope this answers your question.

[Scuba Steve]

Thanks, that's really insightful. I spent a lot of time this evening pulling measurements from the CAD drawings I made of the place and working with an online load calculator (HVAC Load Calculation - Maunualj - Whole House Loadcalc). The results were interesting to me. For one, the heating and cooling loads were not as far off as I thought they would be (2,000BTU more or less). This may be due to the fact that the crawlspace is completely uninsulated. There is nothing underneath the subfloor or around the perimeter.

The addition built about 2003 is in the more SE/SW part of the house and the area that system controls is somewhat larger but its requirements for heating and cooling were actually a bit less than the older part of the house. I suppose it's because it has R-30 and closed cell foam insulation in various parts of the attic (instead of 6" of blown in cellulose) and better insulation in the walls.

I came up with 27,000 cooling BTU for the unit I currently have problems with and 25,000 for the other area that is not being replaced yet. Right now the house has two 3 ton units and it does not run very long before shutting off in summer. Humidity was a major issue before I added the whole house dehumidifier. I sent my drawings and other construction details to the contractors along with a note that I was also interested in dual fuel since the gas line in the attic runs directly to where the air handler is.

I'm looking forward to seeing how much less a smaller system might cost...

[cabmandone]

Originally Posted by Scuba Steve

Thanks, that's really insightful. I spent a lot of time this evening pulling measurements from the CAD drawings I made of the place and working with an online load calculator (HVAC Load Calculation - Maunualj - Whole House Loadcalc). The results were interesting to me. For one, the heating and cooling loads were not as far off as I thought they would be (2,000BTU more or less). This may be due to the fact that the crawlspace is completely uninsulated. There is nothing underneath the subfloor or around the perimeter.

The addition built about 2003 is in the more SE/SW part of the house and the area that system controls is somewhat larger but its requirements for heating and cooling were actually a bit less than the older part of the house. I suppose it's because it has R-30 and closed cell foam insulation in various parts of the attic (instead of 6" of blown in cellulose) and better insulation in the walls.

I came up with 27,000 cooling BTU for the unit I currently have problems with and 25,000 for the other area that is not being replaced yet. Right now the house has two 3 ton units and it does not run very long before shutting off in summer. Humidity was a major issue before I added the whole house dehumidifier. I sent my drawings and other construction details to the contractors along with a note that I was also interested in dual fuel since the gas line in the attic runs directly to where the air handler is.

I'm looking forward to seeing how much less a smaller system might cost...

It looks like you need slightly more than a 2 ton unit. 2.5 ton would probably be a little big but not like the 3 ton you have currently. There isn't normally a substantial difference in cost from the smaller to the larger or at least that has been my experience. Mind you I buy at dealer cost. It all depends on what kind of markup your local is dealing with. Without knowing your home, I'd think 4 ton total would cool it sufficiently with 5 ton being the max. I don't know that the additional cost for the high efficiency furnace will make sense with your lower heating demand. You'll be adding vent pipe (pvc) and extending gas line to it. Both systems will require a drain for condensation so no difference there or very minimal for plumbing. Both will require a secondary drain pan in the event that your primary condensate drain plugs this keeps the water from coming through your ceiling. It might make sense to do something along the line of what I did to that duplex. The other thing to consider would be going with a gas furnace central air system but in your climate a heat pump is a good way to go.

Either way, when you get your revised estimates PM me as I don't have the notifications set to let me know when there's a new comment to a thread. I'd be glad to look it over and give my .02 if you want it. My guess is they'll try to up sell to the 17 SEER with a variable speed air handler but if they are honest they'll tell you that you should replace your duct system with that configuration.