Heat pump replacement, ducts and sizing.

[ShaneMac]

I have been starting to research heat pump replacements. I currently have an old York 2ton and have been looking to upgrade to something more efficient. Being quite old it works well down to about 23F where it starts to struggle and kicks in the backup resistive heat at which time I turn it off and fire up the wood stove. This worked well when my wife was stay at home with kids and I wfh due to covid. Moved start of covid. Now that she is going back to work and I'm getting pressured to start going into the office I'm feeling it would be nice to have a more efficient heat source when not home durning the days and away for christmas etc.

I have had an energy audit done and said the heat load is 10.57kw which is about 36k btu. House is 1200sf with a finished spray foamed basement of another 1200 sf. 2400sq total and 36k btu heating load sounds possible but basements don't seem to have the same heating loads and have replaced old windows with triple glaze and will be doing additional attic blown in insulation.

Of the 8 quotes almost all of them are recommending a 3ton but not sure if my ducts will support it. I have 14 registers fed with 5" round ducts off the trunk. Given each 5" round duct is good for 5cfm that puts me around 700 cfm. The cfm of the 3t air handlers is around 1200cfm and worried about static pressure issues but really all the quotes were just sales men and no testing done. House is a bungalo with the supply truck running down center of house with the 5" rounds coming off of it to each of the rooms. Only 4 supply in the entire basement.

Don't want to pay premium for the Fujitsu or Mitsubishi so primary quotes I'm considering now is the following.

Daikin 3T DZ6VSA361E/DFVE42CP1400, The DZ6VS appears to have better cold weather then the DZ17 but it also comes with a 3.5 ton blower.
Gree Flex 2/3T with either 2 or 3 ton inside coil/air handler. Out door unit is the same.
Midea 2.5Ton runs about same power in cold weather as the Daikin 3T
Midea 3T

What would be some recommended next steps? Verify what my existing duct work would support? No idea of existing CFM but the registers close to air handlier blow like crazy which is on one end of house but other end of house don't feel much movement thru them.

 

[EbS-P]

I just had all my ductwork replaced. Have a 3 ton heatpump and sized according the load calc which said I needed 4 tons. I did not replace the 3 ton unit.

Can you make it work maybe. Work well probably not. If you had 6 inch duct I’d say add a second return and use 4 inch filters or really cheap filters. But with current ducts when when it blows 1200 cfm you will have serious static pressure issues. Ducts and returns will be whistling.

I have spent way more time that the average person educating my self about hvac. My takeaways.

No system can perform to spec on undersized ducts. Variable speed compressors really need variable speed fans that match the compressor. (Check that the green flex really has a variable speed fan that ramps with compressor). HVAC contractors in general are at the bottom of the barrel of the trades. Running Resistive heating some of the time for the coldest 1-2 weeks a year means your system is sized correctly. And the most important. Who is installing the equipment is almost more important than what equipment is installed.

two tons works down to 23. That’s pretty good. A new two ton cold climate unit will do better. Down to single digits F. The cost difference between 2 and 3 tons is substantial. I understand not wanting top tier equipment but I’m. Not sold on the Gree/Midiea systems for cold climates (I really have-not much reading on them. )

If your duct work is more than 30 years old it may be time to upgrade. If you could at a minimum and if you have access to 6 inch. (But at that point unless it’s diy just get the all the ductwork replaced.

Right now I really like the two stage systems. I’m not sure what cold climate products are available as two stage systems. But it’s the sweet spot in terms of value . If you were installing a mini split unit that’s different. (And that might be an option. Keep 2 ton system and add a 1 ton mini split. I’m thinking about that. My 3 ton can’t keep up but I don’t see any better units available now. Adding solar powered mini split interests Me.

It’s not cheap. It is the mostly expensive system that needs regular replacement in a home. And any Joe with a license and enough credit to buy some tools and can get to start the bidding war to the bottom. I spent almost $9899 USD on a ducts and another 5k on a dehumidifier. Current unit is 14 years old. It wasn’t in the budget to replace a m. Undersized bit functional unit. I want 5 more years out of it.

My advice do it right the first time. Duct work should last a long time. Units 15 years of you’re lucky. Be very picky about who you choose to do the work. I ended up in the crawl space swapping leads and foaming up big holes my contractors left. The metal work was good and the install that took 9 days is quality. But some important details were missed.

 

[ShaneMac]

I wish the ceiling was not finished in basement, would be easy to swap 5" to 6" and have thought about it. I'm comparing btu/h by temp on the gree flex 2t vr 3t, Its a bit surprising. Below -10F the output on the 2T is actually more. Load required increases as the temp drops but the output drops so to match if you size for max heat load you so over size everything else. My cooling load is quite small.

I'm leaning more towards the 2T now. I would easily get the fully communicating Daikin if it had good cold weather numbers but regardless to what they say its pretty bad compared to the newer systems. Gree 2T left, 3T right.

 

[EbS-P]

I wish the ceiling was not finished in basement, would be easy to swap 5" to 6" and have thought about it. I'm comparing btu/h by temp on the gree flex 2t vr 3t, Its a bit surprising. Below -10F the output on the 2T is actually more. Load required increases as the temp drops but the output drops so to match if you size for max heat load you so over size everything else. My cooling load is quite small.

I'm leaning more towards the 2T now. I would easily get the fully communicating Daikin if it had good cold weather numbers but regardless to what they say its pretty bad compared to the newer systems. Gree 2T left, 3T right.

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That’s really a no brained for me. At -5F they are putting out the same heat. You won’t ever need 36k buts when it’s 17F. You need you know your design temperature. That’s really the only way to compare. At your outdoor design temp what is the unit capacity.

Not having access to duct runs I’d be tempted to keep getting by on 2 tons. With possibly adding a mini split or just paying for the resistive heat when needed. I hate it when my strips kick on. And they never do now I have an eco bee and a wood stove. The eco bee lets you lock them out when outside is above a certain temp and if you do manual staging allows you set the degree below set point that they will kick on. I set mine to 5. So they only ever come on when the temps is above 30 during defrost. And with a set point of 68 the house has to drop to 63 before they start burning electrons.

 

[ShaneMac]

Closest design temp I can find is -6.34F so can go with -5F. The 3T Midea unit seems to blow the Gree 3T out of the water where at 2T the Gree is better then the Midea.

 

[EbS-P]

Closest design temp I can find is -6.34F so can go with -5F. The 3T Midea unit seems to blow the Gree 3T out of the water where at 2T the Gree is better then the Midea.

Remember a heatpump system can be sized to rely on resistance heating or not. They cost of a larger heatpump vs running trips need to be assessed in some way. I’m sure some hvac pro that really cares has software to do it. But I have not seen any. The pros on HVAC-talk.com can be helpful. But they will say you can’t install 3 tons on a two ton ductwork and that’s where that conversation will go. They don’t think highly of the cheaper end equipment. And won’t give any DIY advice. But it might we worth an ask. Do the systems you’re looking at have ASHRE Matching numbers?

Your load calc says you need 3 tons heating. Your ducts won’t support that. Seems to me that choosing between 2 and 3 ton units on existing ductwork is ignoring the fact that your ductwork will not support the heating demands on your lid calc.

Unless you have evidence that your load calc is off, and it could be, I think you should be looking for ways to get the 36k btus of heat. That means changing something, duct work

 

[farmwithjunk]

Did you already choose a system?

The Gree 2 ton and 3 ton Flexx are the same units, just a dip switch changing their output, which is almost entirely in the upper end when its least needed.

What size are you supply and return trunks? Are the 14 registers all supply or does that include return? If supply thats around 270 square inches, plenty for 3 ton. What size is your filter? That could be a bigger restriction than the ducting.

You can just drill two small holes and test static pressure with a $30 Amazon manometer. From what I've seen a lot of companies don't check static nor do they care if its running high. What do they care if your ECM blower fails in 5 years vs 10? They get paid to replace it all the same.

 

[ShaneMac]

I didn't pick a system yet, but after more review with the updated Gree Flex or maybe just tosot which is a gree flex knock off the air handler has 8 speed settings and same coil inside. I could set it up for 2ton to start and then move to 3 if needed.

The 14 registers are all supply with 5" rounds coming off the main trunk which is 9x22 to start and drops down in size.
Have one small return in basement and 3 large ones upstairs in living room and two in hall way outside the bedrooms. They feed into a 8x21 main return.

I was about to call the company today and just order it. Not sure why but I'm preferring the gree flex over the midea.

 

[ShaneMac]

Filter is 1" 20X20

 

[farmwithjunk]

I didn't pick a system yet, but after more review with the updated Gree Flex or maybe just tosot which is a gree flex knock off the air handler has 8 speed settings and same coil inside. I could set it up for 2ton to start and then move to 3 if needed.

The 14 registers are all supply with 5" rounds coming off the main trunk which is 9x22 to start and drops down in size.
Have one small return in basement and 3 large ones upstairs in living room and two in hall way outside the bedrooms. They feed into a 8x21 main return.

I was about to call the company today and just order it. Not sure why but I'm preferring the gree flex over the midea.

Would it be possible to add another return somewhere and then connect it to the return box with some flex duct?

I think you'd be marginal on your ducting, especially the smaller return. Should work but might be noisy. The Gree allows much higher static pressure than most air handlers and being able to set the fan's max speed will help.

 

[farmwithjunk]

Filter is 1" 20X20

Is 1" the max it will take or just what you are using? A thicker 4" pleated Merv 8 will have the least resistant and still likely filter better than any 1".

 

[ShaneMac]

1" is max it will take but can request a bigger one when doing the install. I use the blown fibreglass ones for min resistance with protection for device but nothing for air quality.

 

[ShaneMac]

I would like to in future add a bigger return in basement as well as supply, there is only two registers in basement currently. I think plan would be to buy it setup for 2ton to worry more about upstairs with wood stove in basement then over time add more return/supply in basement then switch to 3ton. Would that make sense?

 

[farmwithjunk]

A single 8" return would add enough I'd think. That would make your return slightly larger than your supply and would drop down the pressure. You could add this yourself later with a starter collar in the return box and insulated flex duct.

 

[farmwithjunk]

I would like to in future add a bigger return in basement as well as supply, there is only two registers in basement currently. I think plan would be to buy it setup for 2ton to worry more about upstairs with wood stove in basement then over time add more return/supply in basement then switch to 3ton. Would that make sense?

Manual shows about the same CFM regardless of 2/3 ton setting so may as well set it for 3 ton and have more output at a slight cost in efficiency. 2400 sq ft in up north seems like a lot so you must have some really good insulation and sealing. The unit will run at lower settings so not like it goes 100% everytime it kicks on.

 

[ShaneMac]

So confused the difference between the 2/3t air handler or if there is any difference at all besides pre-configured dip switches.

Page 16 of Mr cool shows one setting for dip switch to swap back and forth on fan settings and 2/3 ton modes.
Page 17 has 8 speed settings using same switches which matches what I found on the gree site.

https://mrcool.com/wp-content/dox_repo/mc-uni-ah-im-um-en-01.pdf
https://www.greecomfort.com/assets/our-products/flexx/documents/flexx-quick-start-guide-a.pdf. Page 8 for switches

Would I be better off getting the 2 or 3 ton indoor air handler?

According to Gree
FLEXX24HP230V1BH. 2t Air Handler
FLEXX36HP230V1BH. 3t Air Handler

Even with these they all have different settings on the dip switches so wondering if its a 16 speed fan lol

Especially if the indoor coil is the same, what really could be different?

https://www.tosotcomfort.com/_files/ugd/320e62_d2c42f1a462a46d8a7071a30ce944146.pdf

This manual shows one mode for indoor, with the 16 settings handling 2 and 3ton.

 

[farmwithjunk]

So confused the difference between the 2/3t air handler or if there is any difference at all besides pre-configured dip switches.

Page 16 of Mr cool shows one setting for dip switch to swap back and forth on fan settings and 2/3 ton modes.
Page 17 has 8 speed settings using same switches which matches what I found on the gree site.

https://mrcool.com/wp-content/dox_repo/mc-uni-ah-im-um-en-01.pdf
https://www.greecomfort.com/assets/our-products/flexx/documents/flexx-quick-start-guide-a.pdf. Page 8 for switches

Would I be better off getting the 2 or 3 ton indoor air handler?

According to Gree
FLEXX24HP230V1BH. 2t Air Handler
FLEXX36HP230V1BH. 3t Air Handler

Even with these they all have different settings on the dip switches so wondering if its a 16 speed fan lol

Especially if the indoor coil is the same, what really could be different?

https://www.tosotcomfort.com/_files/ugd/320e62_d2c42f1a462a46d8a7071a30ce944146.pdf

This manual shows one mode for indoor, with the 16 settings handling 2 and 3ton.

Only speaking for the Mr Cool but it should be the exact same even down to the manual. The outside unit has 4 switches, you set your 2/3 ton mode and if you want to change the defrost and efficiency mode. Inside has 8 dip switches. You set your fan speed with the first four but they do not give a setting for the other four ("cool") switches.

I don't think one piece is incorrect in the manual though. They show different CFM depending which ton setting you have. I measured static pressure on both 5 ton (default to higher setting) and on 4 ton. Exact same. I don't think it is smart enough to communicate a change like that either.

Whatever you get I'd suggest a thermostat like the Ecobee, you can change the differential, min on/off times, schedules, ect. That allows you to really control the short cycling that is typical with .5F offsets . Cut down on starting by 60%.

You can use the chat option on any of the sites that sell the equipment to get an answer on the airhandler. They do the same thing with the 4/5 ton system showing 2 part numbers buts the same.

 

[ShaneMac]

Have an ecobee 3 lite now on the old heat pump. Works great. New one comes with same so they are taking it off list so saving another $150 there. Given where the return is I could easily add a 8" in utility room and have it go right to a long 90 and thru wall and it would add a nice return to the basement which is lacking.

 

[ShaneMac]

Ordered the 3t, Thank you for all the help. Will look into converting to 2t in spring for cooling as my cooling load is a lot less.

 

[EbS-P]

Ordered the 3t, Thank you for all the help. Will look into converting to 2t in spring for cooling as my cooling load is a lot less.

I find this option unnecessary if the ramp is done correctly. It should satisfy temp before it turns the output up to 3 ton. But I’m skeptical if it’s done that way.

 

[ShaneMac]

I find this option unnecessary if the ramp is done correctly. It should satisfy temp before it turns the output up to 3 ton. But I’m skeptical if it’s done that way.

Yah that is the tricky part, I want it to run longer getting to temp slower at a lower rate to help in dehumidification.