Go with a newer Heat Pump or say a 90%+ Gas furnace?
I have a 9200sq ft house built in 1999. It has 4 total HVACs, 3 of them being AC/Gas furnace splits. The last one (basement one) is a Heat Pump with 14.4k backup heat strips. The entire attic has also been spray foamed (open cell, about 6") on the rafters, so its a pretty tight house as far as insulation goes, all the wood windoes in about 3-4weeks (the double hungs) will be repaced since the old ones are rotting, some dont open, many are sagging so its not sealing....
Now the basement unit is a 10 SEER 3.5ton Heat Pump, the basement footprint I would say is right around 3000sq ft. The unit is a ICP brand and was put in 2001 from the serial number I see. Recently (previous owners) must have put a Aprilaire 1750 whole house dehumidifier on that same 3.5ton Heat Pump because I think that 3.5ton is over sized. There are a few issues but dont want to dig too much into it, one being there is only about 900 CFM worth of return air but over 1200CFM of supply ducting. I know the unit is starving for air because when we pulled the front panel off while the unit was on, you could tell that all the sudden there was more air going out of all the supply vents. So additional return needs to be added, or correct the sizing.
Ive had about 4-5 quotes for replacement Heat Pump (since I dont think this is operating efficiently for me, we work out of the house, my wife and I, and our offices are in the basement,) so we ask that the unit try to maintain a 68F temp during winter and on colder days here in Atlanta like 30-40F outside, that unit has a cumulative runtime of almost 4-6hrs during just an 8hr period (we set it to say 68F at 8am and tell it to cut back to 62F by 4pm). Few have quoted the budget ones all the way upto the inverter based heat pumps, so the ranges are pretty wild.
Then looking at some open areas of the ceiling (some areas of the basement are unfinished like storage room) there is about a 1.5' gap between the actual basmement ceiling and the 1st floor joists. So I thought maybe we do a gas furnace, like a 95%. Getting a gas line isnt an issue since about 5ft from that unit is a gas line that Ts for my main 1st Gas furnace and a 40gal water heater. So I could T into that. Then looking at that gap in the ceiling, one HVAC guy said he can run the single 2-3" PVC about 40ft down the line and exit out the side of the house where all my AC condensers and pool equipment is. But that will require some cutting up of the drywall in a few places in the ceiling, probably every 8-10ft where he has to put join the PVC pipes or put an elbow in. I looked at the celing area a bit more and I dont think its going to be easily done, probably much more cutting involved, there is already a zoo of 8-10" insualted duct work all around that area so they will have to cut up alot of the area. And not really looking forward to that.
So getting to my main question, now Im thinking of going back to entertaining the heat pump idea. Lets say I go with these 18SEER, 2stage comrpessor (say a 3ton), HSPF of 9.5. How would you compare that to say like a 95% single or two stage 75k btu gas furnace? My electric rates here are between 9-15cents (right now 9 cause its winter, it goes to 15cents in summer during only like 3-7pm peak time). Gas rates are extremely low as well, right now around 50cents a therm. Or is this not as easy to compare these two since it is two different types of furnace. As far as the stages, Im not really concerned with all the hoopla around multi stage or variable speed and "comfort" you get. Just more concerned with heating this space during our working hours efficiently (unlike running for 6hrs during an 8hr period).
Atlanta is known for having very moderate winters with sometimes short winter blasts and very brutal summers.
I would stay with heat pump for basement. I do suspect you are oversized.
Depending on your electric and nat gas rates, I would go 80% eff two stg VS furnaces with high eff heat pumps or high eff furnaces with straight high eff AC. I think 95% eff furnaces with high eff HPs is overkill for Hotlanta location.
Of course, you should insist on load calculation for both heating and cooling. I assume your electric rate in summer is same whether for straight AC or HP condenser.
My ideas. Would like to hear from others.
The electric and gas rates were mentioned in the post, right now around 9cents a KWH. During summer only during peak times of I believe 3-7pm it goes to 15cents/KWH. Right now the Natural Gas rates are in the 50cents a Therm.
I didnt go or entertain the 80% units mainly because the flue issue. Right now the nearest flue is about 6-7ft away, but its only a 5" flue, it is already being shared with a 100k btu 80% gas furnace and a 40k btu gas water heater. So adding another unit to that will push it over the limit on what that 5" flue can take. Trying to run another flue from the basement to the attic is not happening, we looking at close to a 40-50ft run from the basement to the top of the attic peak where the current flue exits. Thats why initially we thought about using a 90-95% high efficiency unit so that we could run a PVC straight down the ceiling in the basement and out the side of the house (but have to cut up a good bit of drywall).
Didnt follow you on what you said about staying with a heat pump but you say I would go for a 80% 2stage gas furnace? Wont be able to do that without a proper flue that can be used. I was basically comparing or looking at say a single or two stage (some only do 2stage units) 95% efficient gas furnace if I decide to give the green light on tearing up half my ceiling drywall in the basement, OR, go with say a 18SEER 2stage Heat Pump (say a 3-4ton depending on brand, some only start at 4stage).
For the most part the 4-5 HVAC companies that have come over have said the current 3.5stage is oversized for a basement, they recommended a 3ton at max. Some said do a 4ton 2stage (lowest size offered on 2stage heat pump). All said when done, we wont need the Aprilaire as it will be useless once the right size unit is installed.
I'd stay with heat pump and change to more efficient drive air handler. Variable drv air handlers remove humidity very fast and with right size outdoor heat pump, you could see allot of savings on system up-grade. I prefer Carrier heat pumps/ variable drv air handlers, but if installed & design properly most systems brands are much the same.Increase the area of return, even if you have to run overhead rectangular duct work. Remember airflow=air changes per hour in the space you are heating or cooling..GL
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Heat Pump vs Gas/AC... good question. IMO, and I used to finish basements before getting into heat and air... the answer is more about the needs of the customer and the home... than a general answer.
Yes, Atlanta is basically an AC market... we do not have harsh nor long winters... yet we do have that COLD night or weekend (like a week or so ago), when extra heat capacity is needed.
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We're in the midwest however with your nat. gas rate (low) and your electric rate, you really need to be heating on gas and if 95% you'll be doing the heating for about 1/2 of the heat pump cost for a million BTUs of heat. My home is about 8cents/kwh and 60cents/therm and the nat. gas will be about 1/2 of the cost of electric. It will only get near even if the temp outside is close to 50 degrees. I'd have to recommend the gas furnace.
X2, heat pumps are very common in the south though and sounds like it will be a good bit cheaper up front for heat pump due to the venting issue.
Originally Posted by wahoo
Easy to oversize in Atlanta. The summer are humid and last a long time, but design temrpatures are a lot lower than many think. No hotter than Norther MO or Souther Iowa, believe it or not. St. Louis for example has a higher desing temp.
IF you have some land space for vertical geothermal wells, you could install chilled water and hot water heating asing hydronic air handlers.
But as mentioned, in your climate, when properly sized for cooling a heat pump can nearly handle the heating load without using much aux elec. back-up, so going dual fuel can save if you have gas already, but for multizone set-up it probably isnt; worht it.
In humid climate, sizing is critical, and oversized system will use more energy than a properly sized on and be a lot less comfortable. You might need as little at 10 tons for hte entire home.
One other thought.... since you combined load is likely over 10 tons, you might look at installing a small air cooled chiller, then using a gas boiler for heating. Then you'd have a single central plant to maintain, rather than 4 seperate compressors. Utilities usually offer rebates of around 10% on the purchase. You might even find that a single 10 ton chiller and 4 hydronic air handlers and some pex piping ot connect them is cheaper than 4 complete systems. Also, the airflow requirements will be lower so the system can be quieter and will dehumidify better.
My vote is geothermal. I'd either go water ot water and install 2 heat pumps for redundanct, or install 4 package units in place of the existing air handler/furnaces.
Good points. On the last one, going a single unit might be really costly up front. The three other units are split up as follows, there is a 4ton cooling unit with a 100k btu gas furnace for most of the main 1st floor. Then there is a 2.5ton cooling unit with a 80k gas furnace dedicated to about 1/3 of the remaing first floor which is mainly the master, master bath, and office. The lastly there is a 3rd unit for the 2nd floor which is a 3ton cooling unit (recently replaced by the previous owner, looks like a budget 13seer comfortmaker r22 system with a new evap coil) with a 100k btu gas furnace. And as we know the basement currently has the 3.5ton heatpump with 14.4k backup heat strips (which I almost never use as I programmed the thermostat for a 4.5F differential before it kicks in).
Main idea is really the best ecomonical/efficient heating. Thats where initially the 95% gas units came into play, except we didnt fully analyze the venting. I did about 1day ago and its going to be tricky and I think they going to have to rip apart about 40-50ft of my basement ceiling drywall to get that 2-3" PVC piping in so it can be vented off the side of the house. Then we talking the cost to redo that drywall, plaster, paint, etc. So that factored in makes it pretty close to say the cost of a nice 18seer 2stage heatpump. But granted the heat pump isnt going to be as (in my opinon, whatever that is worth) efficient when we have these cold nights and weeks like we have had in the past few weeks in Atlanta (btw Im in the Duluth area).
Set backs are not a good idea with heat pumps, it usually costs the same or less to find a temp and leave it unless you are leaving for an extended period 2+ days nights because it has to run much harder for longer to bring it up to temp as well as using the aux heat to catch up. As far as tearing out the ceiling, drywall is a pretty easy task, probably the easiest thing to do in the construction trade. If done well it needs very little sanding. If the run is a straight shot it could all be pushed from outside without having to open up any drywall, or if you have any closets that line up floor to floor to attic the venting could be concealed in a corner of the closet and out the roof.
Originally Posted by Dixit
You could alsways consider installing a wall mount boiler at an outside wall where venting would be easy, then just fishing PEX tubing for the water pipes to the air hander(s). Thsi would be the lowest operating cost back-up heat set-up. With a boiler, you coudl use setbacks without penalty. But it will cost more up front to install.... but this is a 9200sqft luxury home, how cheap do you need to go? As you rennovate room in the future, you could also install in floor radiant heat as well. In warm climates I'm think that tile floors would be nice, since they'd feel cool in summer, but in winter could be heated.
Motorguy, good points there. I'm definitely not interested in going cheap in a luxury home. That's why we started off doing 6" of spray foam in the attic. Then we are replacing about 30 double hung windows in a few weeks. All my existing double hungs are wood and some rotting, sagging, not sealing properly, seals on the double pane glass broken.
The floor radiant heating is interesting. I know my uncle has it in his house in long island and that is basically his main heat source. My house has 2500sq ft of wood floors so probably can't do floor heating there. But definitely do able in the foyer where its all natural tile and the master bath which is large and tiled.
I need to take another hard look at the drywall aspect again. I agree with the other person that it's not the worst thing to rip it up and put it back, it is one of the easiest thing to fix and get back to original state. The 95% furnace definitely interests me and say doing the 2stage compressor for cooling to help with the dehumidification of the basement. That will allow me to get rid of the Aprilaire central one they put in a few years ago that is piggybacking the heat pump.
Start with heat loss calculations after the building envelope improvements are done. Until you understand the proper size equipment, you are guessing at need. If it is a full undergound basement, you might be surprised if all you really need is a proper dehumidifier and possibly a mini-split heat pump.
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