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  1. #1
    Join Date
    Feb 2013
    Location
    SW Virginia
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    11

    Getting a little frustrated about this whole heat pump ordeal!

    Why can't I live closer to someone on the contractor map!

    I've gotten five quotes for a new heat pump and no one has mentioned a Manual J. I asked the guy today about it and he chuckled as he said, "it'll cost you a few hundred dollars." He said he'd "like to set me up with a 4 ton unit." All he had to go by was my house square footage, the # of registers I had, and the fact I currently own a 3.5 ton unit.

    The Trane contractor I have the best feeling about thinks they can look at my house blueprints and do a load calculation. They come highly recommended but they just go by the rule of thumb sizing method. I'm still willing to do business with them because they offer a 10 year labor warranty, had the most reasonable price, and I just get a good vibe from the guy. He guarantees me he will do a good job but I am still concerned if I'd be getting the correct size unit.

    I've called someone on the contractor map but he doesn't want to make the drive to perform a Manual J. I've called a local energy consultant about a manual J and they were trying to get me to do a blower door test and then a Manual J....that's several hundred dollars. Honestly, I don't think it's worth the money.

    I took Baldy's advice and downloaded the HVAC-calc program but feel uncomfortable doing that correctly.

    I was settled on the 16 or XL20i but since they don't come in half tons, maybe I should go with the XL15i in 3.5. Maybe 3.5 is too big for my home right now but it seems to be doing fine...other than being older than dirt.

    Any advice?

  2. #2
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,371
    If your load did come out to 3.5 tons, a 4 ton XL20i would be no problem if the ductwork could support a 4 ton system. Considering your location the somewhat higher heating capacity would be beneficial. And the actual rated capacities of the 4 ton XL20i heat pump and TAM8 air handler are actual a bit shy of the nominal 4 ton capacity (48,000 btu/hour). I made the same decision. Manual J came out to 3.7 in my case, and the 4 ton has worked great. You will achieve longer runtimes with the 2 ton compressor, and the system should be very quiet and provide even, comfortable temperatures. Of course proper set up, sizing, and ductwork design are all necessary factors to allow for this.

  3. #3
    Join Date
    Feb 2013
    Location
    SW Virginia
    Posts
    11
    Quote Originally Posted by RyanHughes View Post
    If your load did come out to 3.5 tons, a 4 ton XL20i would be no problem if the ductwork could support a 4 ton system. Considering your location the somewhat higher heating capacity would be beneficial. And the actual rated capacities of the 4 ton XL20i heat pump and TAM8 air handler are actual a bit shy of the nominal 4 ton capacity (48,000 btu/hour). I made the same decision. Manual J came out to 3.7 in my case, and the 4 ton has worked great. You will achieve longer runtimes with the 2 ton compressor, and the system should be very quiet and provide even, comfortable temperatures. Of course proper set up, sizing, and ductwork design are all necessary factors to allow for this.
    I guess it's still a possibility that a 3.5 ton is over sized for my home? I mean I know there are other factors but a 2200 square foot home should be close to being 3.5 ton, right? (I have absolutely no figures to support this argument )

  4. #4
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
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    3,371
    Quote Originally Posted by Finch View Post
    I guess it's still a possibility that a 3.5 ton is over sized for my home? I mean I know there are other factors but a 2200 square foot home should be close to being 3.5 ton, right? (I have absolutely no figures to support this argument )
    Yes it certainly is. A Manual J needs to be done, but sounds more like a 3 ton situation to me (again just a guess until a load calculation is done). 2-stage isn't a reason to oversize. Sorry you are having trouble finding a competent dealer who can perform this task for you before installing a new system.

  5. #5
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,720
    Hate you're having trouble finding a contractor to calculate the load. It only takes 10-15 minutes to do a quick block load by hand once you have all the measurements, rvalues, ect. With a good load calc program you can do a room by room and duct layout in about the same amount of time.

  6. #6
    Join Date
    Feb 2013
    Location
    SW Virginia
    Posts
    11
    What if I just got them to install a 3 ton unit with the possibility of it being undersized? I read that being on the under side is better than being over.

    On another note, whichever size I do go with, I'm definitely thinking about the 5" media filter. It is my understanding that I won't need to use a filter in the two return grills, right? They currently are not filter grills and the contractor quoted me a price for replacing these grills with replacement filter grills. They are not a standard size either, 24x16 I believe. Would that even be needed if I went with the 5" media?

    Humidifier worth the extra price?

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,271
    Quote Originally Posted by Finch View Post
    Why can't I live closer to someone on the contractor map!

    The Trane contractor I have the best feeling about thinks they can look at my house blueprints and do a load calculation. They come highly recommended but they just go by the rule of thumb sizing method. I'm still willing to do business with them because they offer a 10 year labor warranty, had the most reasonable price, and I just get a good vibe from the guy. He guarantees me he will do a good job but I am still concerned if I'd be getting the correct size unit.

    I've called someone on the contractor map but he doesn't want to make the drive to perform a Manual J.

    Any advice?
    What is your perception of the validity of performing calculations using drawings and specs for new construction?

    Windows size/type/orientation and infiltration are THE SIGNIFICANT Factors in determining overall heat gain.

    What is the usual Relative Humidity for your home in July and August?

    _Virtual HVAC_ is also a fourth or fifth option for determining heating and cooling loads.

    There are usually nearly a dozen ways to check and cross check loads in the world of thermal building envelope evaluations.
    One of them being _ current energy use. ... ... ...
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  8. #8
    Join Date
    Feb 2013
    Location
    SW Virginia
    Posts
    11
    Quote Originally Posted by dan sw fl View Post
    What is your perception of the validity of performing calculations using drawings and specs for new construction?

    Windows size/type/orientation and infiltration are THE SIGNIFICANT Factors in determining overall heat gain.

    What is the usual Relative Humidity for your home in July and August?

    _Virtual HVAC_ is also a fourth or fifth option for determining heating and cooling loads.

    There are usually nearly a dozen ways to check and cross check loads in the world of thermal building envelope evaluations.
    One of them being _ current energy use. ... ... ...
    With the little bit I know about HVAC, I wouldn't even think there is much validity even with new construction. That was my feeling when the contractor asked to see the blueprints to my 1979 home. I apologize if my post did not convey that.. I realize there is a lot more to it.

    I believe the average humidity for my area in July & August is 70 deg. I just googled it for both months and took the average between the morning and evening humidity.

    If I was to take measurements of my current ducts/returns, would you guys be able to inform me if my ducts are undersized for a 4 ton unit?

    Also, still wondering about if I need to use filters in my returns if I have the 5" media filter. I've read conflicting reports.

  9. #9
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,271
    Quote Originally Posted by Finch View Post
    With the little bit I know about HVAC, I wouldn't even think there is much validity even with new construction. That was my feeling when the contractor asked to see the blueprints to my 1979 home. I apologize if my post did not convey that.. I realize there is a lot more to it.

    I believe the average humidity for my area in July & August is 70 deg. I just googled it for both months and took the average between the morning and evening humidity.
    I guess to some Science may always be Fiction.
    It not worth the effort to even try to convey any engineering principles to a non-believer
    / one who will remain Lost.

    One needs to REALLY work on REDUCING the relative humidity (R.H.) IN your house.
    R.H. should be < 45%.
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  10. #10
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Quote Originally Posted by Finch View Post
    If I was to take measurements of my current ducts/returns, would you guys be able to inform me if my ducts are undersized for a 4 ton unit?

    Also, still wondering about if I need to use filters in my returns if I have the 5" media filter. I've read conflicting reports.
    No, if you have a media filter, no meed for the 2nd level of filtration. You can always go up to a MERV 11-13 range. I don't see any point beyond that. HVAC is not a dust collector. That's what vacuum cleaners are for. Get a nice Dyson and use it regularly, 10X better overall results than the best air filter. I suppose someone might argue that then you'll have dust left in your return duct. Ummmm... you will ALWAYS have dust in all ductwork no filter is 100% except those used for commercial HEPA systems for clean rooms like phamaceutical mfg and surgical rooms in hospitals and even those are about 99.99999% effective.

    For the ductwork. A simple calculation is to measure the cross sectional area in aquare inches, then divide it by 144 ot get square feet. Now, you need ot know the CFM requirements for that duct. A best estimate of the proportional amount of air going through it... ie if you have 10 registers and they all have about the same airflow, then if you have a 3 ton unit, 120CFM is going through each branch. IF a trunk has 6 supplies, it needs to carry 600 CFM.... etc. Now take the CFM and divide it by hte cross section area in square feet (remember all the Algebra stuff... funny how it can come in handy). You taking Cubic Feet/Minute and dividing it by Feet^2... os now you get Feet per Minute... or velocity. The maximum recommended velocity for supplies is 900 FPM. <700 is ideal. For returns is 700FPM... <500 is ideal. At those ideal velocities, the airflow becomes almost silent with a modest amount of insulation (lagging) in the supply and return plenums.

    For for 4 ton (1600 CFM) you need at minimum 1.8 sqft of duct area for supplies and 2.3 sqft for returns.

  11. #11
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Keep in mind that you current unit, if more than 10 year old, is probably only 8-12 SEER and has a much smaller indoor coil surface are. thsoe older system because of that smaller coil, did a better job dehumidifying. Actual compressor effciency hasn't increased all that dramatically, they are mostly just giving you more copper and aluminum now and using higher effciency condeser fan motors and indoor blower motors. That's hte main advantage of the XL20i. On low stage, the single compressor now has a huge outdoor coil when cooling and hte condenser fan and run at a super low speed using maybe 10-15 watts as opposed to almost 100 watts on high speed in hot weather. Indoors, on low stage the blwoer might only need 50Watts to move the air, so even if it runs twice as long, on high stage the blower might use 120 watts, so your clearly saving energy.

  12. #12
    Join Date
    Feb 2013
    Location
    SW Virginia
    Posts
    11
    Quote Originally Posted by dan sw fl View Post
    I guess to some Science may always be Fiction.
    It not worth the effort to even try to convey any engineering principles to a non-believer
    / one who will remain Lost.

    One needs to REALLY work on REDUCING the relative humidity (R.H.) IN your house.
    R.H. should be < 45%.
    Look, I'm not trying to dispute what you are saying. Hell, that's the whole reason I'm posting because I just don't want to take someone's word for it that I need a certain size unit. Maybe I misunderstood your question but "I" would think someone would need more than blueprints to figure the correctly sized unit.

  13. #13
    Join Date
    Feb 2013
    Location
    SW Virginia
    Posts
    11
    Quote Originally Posted by motoguy128 View Post
    Keep in mind that you current unit, if more than 10 year old, is probably only 8-12 SEER and has a much smaller indoor coil surface are. thsoe older system because of that smaller coil, did a better job dehumidifying. Actual compressor effciency hasn't increased all that dramatically, they are mostly just giving you more copper and aluminum now and using higher effciency condeser fan motors and indoor blower motors. That's hte main advantage of the XL20i. On low stage, the single compressor now has a huge outdoor coil when cooling and hte condenser fan and run at a super low speed using maybe 10-15 watts as opposed to almost 100 watts on high speed in hot weather. Indoors, on low stage the blwoer might only need 50Watts to move the air, so even if it runs twice as long, on high stage the blower might use 120 watts, so your clearly saving energy.
    Thanks for your help, motoguy128!

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