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Old 01-06-2018, 04:21 PM   #61
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I am going to assume the Op may be a bit confused by now...Earlier in this thread it was a majority vote it seemed that a 4 ton was way way over kill and was Not Recommended by no means and now since the contactor that has suggested this from their software it Could Now be acceptable...I am confused myself whats changed here...maybe im missing something..I hope I don't seem rude asking..
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Old 01-06-2018, 04:30 PM   #62
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Re: System Sizing


Don't know, i've always thought 4 ton was overkill and listed the reasons why it's a bad idea.

New information though is that it's a heatpump application.

In that case sizing is a balancing act, the higher capacity can help reduce the use of very expensive backup heat.

So if the air ducts are okay for 3 tons, it may make sense to get a 3 ton 2-stage.

The op could drop from a 3 ton to a 2 ton hp and have the heating bills skyrocket despite getting a more efficient machine because of all the extra resistance heat needed to maintain the setting.
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Old 01-06-2018, 04:44 PM   #63
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Re: System Sizing


It happens. Sometimes we get carried away. However in this case, we are talking about a few completely different cases.

1) AC only. 2-2.5 ton was suggested.
2) standard heat pump. 2-3 ton, depending on backup heat
3) inverter heat pump. They work better when oversized compared to single speed units. They handle the balancing act better. User is right that the ductwork would likely need modification for optimal performance. They are expensive to buy and repair, but do save a bit in electricity.

Cheers!
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Old 01-06-2018, 04:50 PM   #64
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Actually I believe I suggested a 4.5 to 5 ton for this off the top of my head.. I gave a little wiggle room for possible future upgrades..lol..I did suggest in that as well that a proper sizing calculation needed to be preformed..If it was me and I was not in the business of HVAC ...I would get a couple more contractors to come out and make a bid then compare and go with the most sensible one..It is harder for us online to suggest then someone there in person looking at the project first hand..imo anyway
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Old 01-06-2018, 05:13 PM   #65
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Re: System Sizing


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Originally Posted by Mikel7829 View Post
Actually I believe I suggested a 4.5 to 5 ton for this off the top of my head.. I gave a little wiggle room for possible future upgrades..lol..I did suggest in that as well that a proper sizing calculation needed to be preformed..If it was me and I was not in the business of HVAC ...I would get a couple more contractors to come out and make a bid then compare and go with the most sensible one..It is harder for us online to suggest then someone there in person looking at the project first hand..imo anyway
I do believe a 4.5-5 ton would be too big. The 4 is stretching it as it was, and that's too maintain heat during cold spells.

Yes, a seasoned pro will be able to run a load calc with more accuracy then a DIY'r. However, most won't do a calc, either because they charge more for that, or simple don't want to.

Don't forget that this is a DIY site, and there's been a few on here that have installed their own systems. For better or for worse. There's a few DIY'rs on here that do better then 4th year apprentices. Some people just need a little guidance and they do well. Others need to call a Pro.

Cheers!
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Old 01-06-2018, 05:44 PM   #66
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Quote:
Originally Posted by Mikel7829 View Post
Actually I believe I suggested a 4.5 to 5 ton for this off the top of my head.. I gave a little wiggle room for possible future upgrades..lol..I did suggest in that as well that a proper sizing calculation needed to be preformed..If it was me and I was not in the business of HVAC ...I would get a couple more contractors to come out and make a bid then compare and go with the most sensible one..It is harder for us online to suggest then someone there in person looking at the project first hand..imo anyway
I do believe a 4.5-5 ton would be too big. The 4 is stretching it as it was, and that's too maintain heat during cold spells.

Yes, a seasoned pro will be able to run a load calc with more accuracy then a DIY'r. However, most won't do a calc, either because they charge more for that, or simple don't want to.

Don't forget that this is a DIY site, and there's been a few on here that have installed their own systems. For better or for worse. There's a few DIY'rs on here that do better then 4th year apprentices. Some people just need a little guidance and they do well. Others need to call a Pro.

Cheers!
Is the one that suggested to him a 4th year apprentice?
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Old 01-06-2018, 05:52 PM   #67
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Re: System Sizing


There are probably some DIY'ers that can do better than the bottom 40% of trades people out there who completed apprentiships. Especially on proper sizing and commissioning, evaluating air ducts.

Experience alone is no indicator in itself.
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Old 01-06-2018, 05:57 PM   #68
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Originally Posted by user_12345a View Post
There are probably some DIY'ers that can do better than the bottom 40% of trades people out there who completed apprentiships. Especially on proper sizing and commissioning, evaluating air ducts.

Experience alone is no indicator in itself.
Oh I agree...schooling mean zip in some cases ...Common seanse trumps 10 fold....
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Old 01-06-2018, 07:34 PM   #69
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Re: System Sizing


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I do have issues with noise out of the closest supply vent which makes me alter the damper. We actually don't use AC that much in the summer since we live in the woods and have substantial shade. On the hot/humid summer days when we run it we usually set it to 78. We use ceiling fans all the time instead. Thanks again for everyone's insight.
Thats why you probably don't have severe humidity problems in the summer.

A 4 ton unit will be twice as loud at those registers as you have now. Plus be loud at more registers.
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Old 01-06-2018, 08:08 PM   #70
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I do have issues with noise out of the closest supply vent which makes me alter the damper. We actually don't use AC that much in the summer since we live in the woods and have substantial shade. On the hot/humid summer days when we run it we usually set it to 78. We use ceiling fans all the time instead. Thanks again for everyone's insight.
Thats why you probably don't have severe humidity problems in the summer.

A 4 ton unit will be twice as loud at those registers as you have now. Plus be loud at more registers.
Its fairly simple to slow down the airflow to reduce un-wanted noise level..I believe you are aware of that..In my opinion I will stand behind my first recommendation around 4.5 tons..4 would be fine..Like stated I have wiggle room I know in this feild we all do different things..different ways..ect Its just the way it is..everyone theories are different on what works the best so on and so on..I am not singling anyone out but most of us don't want to be wrong..I am guilty of it myself but thats how it goes I guess...I notice everyone seems to go against others right or wrong..I dont know maybe its me maybe im reading to much into it..But there is no way I would put anything less then a 3.5 ton in the op's said house..period ..I do apologize if I made anyone mad in this thread...was not my intension
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Old 01-06-2018, 08:22 PM   #71
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Re: System Sizing


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Originally Posted by Mikel7829 View Post
Its fairly simple to slow down the airflow to reduce un-wanted noise level..I believe you are aware of that..In my opinion I will stand behind my first recommendation around 4.5 tons..4 would be fine..Like stated I have wiggle room I know in this feild we all do different things..different ways..ect Its just the way it is..everyone theories are different on what works the best so on and so on..I am not singling anyone out but most of us don't want to be wrong..I am guilty of it myself but thats how it goes I guess...I notice everyone seems to go against others right or wrong..I dont know maybe its me maybe im reading to much into it..But there is no way I would put anything less then a 3.5 ton in the op's said house..period ..I do apologize if I made anyone mad in this thread...was not my intension
You slow down a 4 ton heat pump units air flow to that of a 3 ton. You get high pressure lock outs in the milder temps of spring and fall.

The OP already has an over sized unit, on under sized duct work, so air flow with a 4 ton without duct modifications would probably be reduced to less then 1200 CFM. And he would end up with a conversation piece. Instead of a reliable heat pump system.
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Old 01-06-2018, 08:24 PM   #72
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Re: System Sizing


At 78 it's almost not worth turning on at all.

Overall, it sounds like heating is more of a priority than cooling.

What kind of backup heat do you have? is it a dual fuel or propane/oil or do you have an air handler heat strips?

Whether to stay with 3 ton may depend on if it's an all electric system or not. The oversizing for cooling is justified if it means using less strip heat.

I most certainly would not go for 4 ton, that may be the appropriate size for this house in a brutal climate with air ducts in an attic. I think you can slow the fan down to only 1350 to 1400 cfm without running into issues.
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Last edited by user_12345a; 01-06-2018 at 08:27 PM.
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Old 01-06-2018, 08:33 PM   #73
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Quote:
Originally Posted by beenthere View Post
Quote:
Originally Posted by Mikel7829 View Post
Its fairly simple to slow down the airflow to reduce un-wanted noise level..I believe you are aware of that..In my opinion I will stand behind my first recommendation around 4.5 tons..4 would be fine..Like stated I have wiggle room I know in this feild we all do different things..different ways..ect Its just the way it is..everyone theories are different on what works the best so on and so on..I am not singling anyone out but most of us don't want to be wrong..I am guilty of it myself but thats how it goes I guess...I notice everyone seems to go against others right or wrong..I dont know maybe its me maybe im reading to much into it..But there is no way I would put anything less then a 3.5 ton in the op's said house..period ..I do apologize if I made anyone mad in this thread...was not my intension
You slow down a 4 ton heat pump units air flow to that of a 3 ton. You get high pressure lock outs in the milder temps of spring and fall.

The OP already has an over sized unit, on under sized duct work, so air flow with a 4 ton without duct modifications would probably be reduced to less then 1200 CFM. And he would end up with a conversation piece. Instead of a reliable heat pump system.
. Like I said mod the duct work a bit would be fairly easy for the upgrade..I didn't say just install using existing duct the way it is..
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Old 01-06-2018, 08:42 PM   #74
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Not sure if you understand my meaning of slow down..I am talking about upsizing the volume of the first several feet of supply then taper down to the existing size of the supply...Then of course open up the volume of the return how needed..See what Im saying?
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Old 01-06-2018, 09:45 PM   #75
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Re: System Sizing


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Not sure if you understand my meaning of slow down..I am talking about upsizing the volume of the first several feet of supply then taper down to the existing size of the supply...Then of course open up the volume of the return how needed..See what Im saying?
You increase unit size by 1 ton, which in this case, is a 33% increase. You need to do a lot more then just increase trunk size for a few feet, and add a little more return.

Would need to add more supplies, which means increasing the size of the entire supply trunk. And add more returns from the house.
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