Switching from AC to heat pump - need help in sizing.

8 years ago

I currently have a 10yo 3.5 ton York AC unit, with a gas furnace. And because I'm having issues with the AC unit, I'm planning on going to a dual fuel setup with a heat pump with my existing gas furnace.

The house is a 2400sqft, not including the basement, and at the time of build, it was an EPA energy star certified home. The basement is not finished either....

The 3.5 ton AC unit has been able to keep the house cool, but it seems to run non-stop.. This is fine, since my cooling costs were low... It was lower than a 1200sqft townhome I was in. My issue has been the cost to heat. My furnace is Propane gas... Gas has been a killer in cost... So I'm hoping a dual fuel would help....

Based on my existing AC unit, 3.5 tons is fine .. It seems to run non-stop, but that pulls the moister out of the air... Still, it does drive me a bit nuts because the unit is outside my family room window.... It's real bad when it rains because I hear the rain drops pinging off the fan as it spins...

This unit is located on the North side of my home (I'm in in MD, just at the PA line), next to my drive way, so it gets little full sun. My plan is to move the new unit to the south side of my home, where it's full sun for most of the day..

With that said, would I be better off going with a 4TON compressor? I'm thinking 4T to help with heating, and being it's going to be in full sun, it's cooling capacity won't be as good during the summer... Plus, 4T might be better for when the basement is finished...

Maybe my thinking is all wrong and I should still stick with the 3.5T unit, since my plan is to use the gas furnace when temps drop below 35F..

What are your thoughts and why? Which would be a better setup for dollar savings?

Thanks All!!

Sort by:Oldest

Comments (17)

tigerdunes
8 years ago
last modified: 8 years ago
What size furnace/brand/model number and the rated size of the furnace blower? You may be limited to a 3 1/2 ton HP condenser. What is electric rate? You are on the right track. You will need a DF thermostat with outdoor sensor.

IMO
crab_dae
Original Author
8 years ago
I've got huge furnace.. It's a York Diamond 90 Model # p3urc14n09501e. Not sure on the blower rating, but I know it's not variable.

To be honest with you, I have no idea what the they charge for electric here... I just know the propane bill is a killer, so I figured that replacing the AC with a heat pump isn't much more so I'd go that route and have the heat pump option for when I need heat down to 40F or maybe down to 35 F... Anything below those temps would be back on propane...

For the thermostat, I'd like opinions.. I've been told the best is a Honeywell Prestige IAQ, but I'm having a hard time swallowing paying more then $200 for a thermostat. Do you have idea on a thermostat setup that will run me less than $200?

Thanks!
Related Discussions
help deciding between heat pump and a/c
Q
Comments (11)
tigerdunes, I do not currently have an a/c unit. He did tell me the G71 is being discontinued. I have thought about going with the SL280 which is 80% AFUE, but if going with the heat pump i can only assume i will be using this furnace a couple weeks out of the year so it should not reall matter with the lower afue. But on the flip side isn't that counter productive when I am trying to go with a duel fuel source to hedge again energy costs. I think the rates above are petty accurate as I don't have them handy at this moment. I also realize the costco rebate is not free but might come in handy when negotiating prices. Thanks for your help.
...See More
Advice please - Switched from heat pump to high efficiency Trane
Q
Comments (3)
I'm not sure how a modern heat pump compares to a high efficiency furnace running cost wise, but I would imagine that a properly running one ought to cost less to run than just a furnace and you have the added advantage of electricity being able to be generated a number of ways versus your furnace runs on gas or gas you have no choice (I'm thinking along the lines of the price of oil/natural gas vs electricity) Don't forget that a heat pump has the advantage of being able to take advantage of 'free' energy out there (existing heat in the outside air) which raises its efficiency quite a lot, people will argue, for example that a heat pump is "300% efficient" on the face of it impossible, they mean you get three times the heat for the same amount of electricity than if you used the electricity to just generate heat through heating elements. What you've described is confusing, more details if you can please.
...See More
Confused! Pls. read and help us decide- Trane a/c or heat pump??
Q
Comments (8)
We live 20 miles south of Houston. Our home is 45 years old, Brick with 2,345 square feet living area. We are all electric, no gas on the property. Our A/C is a 4 ton with electric heat strips that was installed in 1992. We have done everything the utility company recommends to make out home energy efficient. We still get over $800 electric bills. I have a bid from Trane dealer. (Home Depot) The salesman said our current A/C was a 10 SEER when installed and loses 4% per year. So using his figures I a running at about a 4 SEER. He proposes to install either a TRANE XL14i for $8,123.45 or an XL16i for $9,775.00. Also an air handler to match with 20 kWh of heat strips. All the above is with the ten year parts and labor extended warranty from Trane. They also want to service the new unit twice a year for $149 per year. We are currently paying .155 per kWh. Two questings. How much can I realistically expect to save on my electric bill with either of these two units and is the price reasonable.
...See More
need new A/C -switch to heat pump? - central Ohio
Q
Comments (2)
Throw out the bid that wants to install a 3 ton a/c on a furnace that only has the capacity to move 2 tons of air. You currently have a 1.5 ton unit. You cannot double this size. Not only is it not warranted, but your ductwork would not handle the extra airflow. Looks like the quick 500 sqft per ton rule, which is highly inaccurate. The 15 SEER heat pump would only be 15 SEER (or close to it) if the new furnace also had a variable speed fan motor. I think for others to advise you on the payback/savings part of your question, they'll need to know your current gas and electric rates.
...See More
tigerdunes
8 years ago
You need to find out the particulars on your furnace.

model, size, eff, and blower rating size. Your job, not mine.

If keeping your existing furnace, I would stick with 3.5 ton HP condenser. It appears you have conventional blower motor so that limits you to a 13-14 SEER HP condenser with matching evap coil. Because of that, you are not limited to a York brand but I would want a condenser that has electronic demand defrost. That's a must!

no need for HW Prestige 2.0 Thermostat. Overkill for your application. I will come back with recommendation. You will definitely though need an outdoor sensor for a minimum of DF control.

iMO
crab_dae
Original Author
8 years ago
The new heat pump I'm going with is a Goodman SSZ14... No demand defrost, but I know Goodman makes a couple of add-ons for dual fuel and to take outside temps.. But I'd rather have the thermostat handle it. I do plan on eventually getting demand defrost added... White-Rodgers has a universal demand defrost board now.. I'll probably add it next year.

I think my biggest issue now is getting a thermostat that will have an outside sensor, so I can set it to switch to the furnace at whatever temp I set it at... and figuring out whether if I should go with a 3.5 or 4 ton unit... Initially I was going to stay with a 3.5T compressor, but with it running so long, I feel it might be a bit undersized ... But it keeps the house cool, so maybe it's not undersized... A bigger HP would have the benefit of better heat, but I'm worried about it short cycling in the summer.... I wish I knew someone with the same house that had just a heat pump.. but being these homes were Energy star certified homes, I think the build did gas heat and ac ... never did a heat pump or dual fuel.... Oh Well...

Please let me know what Thermostat you recommend.

Thanks!
crab_dae
Original Author
8 years ago
last modified: 8 years ago
Got some info...

I just checked to see how long my current AC compressor ran.. It's 73F outside .... I have the thermostat set to 73F and it ran for 13 mins at midnight... It was off for 9 mins before it just kicked back on. During the daytime, it does run longer... feels like it never shuts off.

Based on that, could or should I go to a 4 ton unit or should I stick with a 3.5ton unit?

BTW, anyone know if the Rheem RP14 has demand defrost? If it does, I might go with it instead of the Goodman SSZ14...

Thanks!
tigerdunes
8 years ago
last modified: 8 years ago
I would rather see you do this right. Third party add ons can be problematic. Look at Trane XR14 HP and identical equivalent from sister company American Standard with their matching evap coil. These models have demand defrost. Demand defrost eliminates/reduces unnecessary defrost calls which can be expensive in your case since your backup is propane. Even York has HP condensers with demand defrost. On thermostats, other than DF capability, are there any other features you are looking for?

as far as sizing, until you properly identify your furnace's blower rating size, I would stay with 3 1/2 ton condenser. You can not tell what the correct condenser size is in a low demand situation like you described above. Have a load calc performed if in doubt.

IMO
mike_home
8 years ago
You should do a load calculation as Tigerdunes suggested. Find a contractor who will do this, or you can get the software for $50 and do it yourself.
crab_dae
Original Author
8 years ago
Guys... it looks like I'm limited to 3.5t.. I found some old literature and it says my furnace is rated for 2.5-3.5 tons. I called York and was told 1200CFMs..

With that known.. does anyone feel the new Rheem RP14 is better or same as the Goodman SSZ14?
tigerdunes
8 years ago
Relatively new model...not much field history on the RA14...
crab_dae
Original Author
8 years ago
last modified: 8 years ago
Tigerdunes... Do you know of I there's kit for the RP14 for demand defrost? If it has it, I'm just going to go with Rheem... If not, I'll go with with the Goodman..

Also, got any recommendations on a thermostat for dual fuel? I just need one with an outside temp sensor, so I can set it where anything below 40F switches to the furnace... The only thing my current thermostat has is being able to program what I want on different days, so any extra features would be nice ... especially wifi so I can control it from my phone or something..

BTW, I did call 2 dealers and none of them knew if there was a demand defrost kit available for the RP14.. I've sent an email to Rheem, and I haven't heard back.. I do see Rheem demand defrost boards online, but I have no idea if they will work on the RP14.

Thanks!
tigerdunes
8 years ago
I will need to check that out to confirm. I would prefer the Rheem to the Goodman. Still not my first choice though.

TD
d2305
8 years ago
Look up reversing valve problems before you get a heat pump.http://www.loadcalc.net/index.php
tigerdunes
8 years ago
I am told that the RP14 does have demand defrost. Also, I am told aluminum evap coils are available. You should insist on this. And finally ask Rheem dealer what HSPF heating efficiency can you expect and to document source of that information. It should come from AHRI directory.

IMO
tigerdunes
8 years ago
More info...

Yup, same demand board the RPNL used.

The RCF coils and the new line of air handlers are all aluminum and have bolt on TXVs....

TD
crab_dae
Original Author
8 years ago
Thanks TD!!
tigerdunes
8 years ago
If going with Rheem, insist on the best applicable RCF all aluminum coil. Check warranty. And get the matching AHRI number with the HSPF heating efficiency.

IMO
crab_dae
Original Author
8 years ago
Tigerdunes,

After going crazy about finding an uncased ADP coil, which I can't seem to find, I think the 4TON Rheem cased coil will work with minimum fabrication to get it to work... The Rheem RCF4821STAMCA, is one of the coils Rheem recommends for it but I have one issue with it...

The suction side is only 3/4" on the coil, not the 7/8" like on the condenser side.. I guess this would be ok, or they wouldn't have done it, but which side should I put the reduce on? .. I guess I'm asking should I use a 7/8" line to the coil and use the reducer there or should I use a 3/4" line and use the reducer on the heat pump side?

I'm kind of shocked that Rheem has setup the HP for 7/8", but 3/4" on the coil side...

Rheem RP1442AJ1NA 3 1/2 Ton, 14 SEER, Single-Stage Heat Pump

Rheem RCF4821STAMCA 3.5 Ton to 4.0 Ton Cased Multi-Position Evaporator Coil

Thanks!

Switching from AC to heat pump - need help in sizing.

Comments (17)

tigerdunes

crab_dae
Original Author

Related Discussions

tigerdunes

crab_dae
Original Author

crab_dae
Original Author

tigerdunes

mike_home

crab_dae
Original Author

tigerdunes

crab_dae
Original Author

tigerdunes

d2305

tigerdunes

tigerdunes

crab_dae
Original Author

tigerdunes

crab_dae
Original Author

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

Switching from AC to heat pump - need help in sizing.

Comments (17)

crab_daeOriginal Author

Related Discussions

crab_daeOriginal Author

crab_daeOriginal Author

crab_daeOriginal Author

crab_daeOriginal Author

crab_daeOriginal Author

crab_daeOriginal Author

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

crab_dae
Original Author

crab_dae
Original Author

crab_dae
Original Author

crab_dae
Original Author

crab_dae
Original Author

crab_dae
Original Author

crab_dae
Original Author