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MattR757, HVAC Technician
Category: HVAC
Satisfied Customers: 52
Experience:  18+ Years experience in residential and commercial HVAC service and repair
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# Im trying to decide what size heat pump to install. We are

### Resolved Question:

I'm trying to decide what size heat pump to install. We are planning on installing 2 smaller heat pumps instead of 1 large heat pump for our 2356 sq ft. main floor. Different contractors have rec. different sizes. I calculated my own heat load calculation using a program called HVAC computer to give me some sort of idea. No contractor in my area does a heat load calculation (we've tried 5). We have decided on using 2 smaller heat pumps instead of 1 larger heat pump as a safety net in case one breaks down.

Heat pump #1 will need to supply 1,424 sq feet with a total heat gain of 18,803 BTUH, sensible gain of 15,726 and heat loss of 46,462 BTUH.

Heat pump #2 will need to supply 933 sq feet with a total heat gain of 15,419 BTUH, sensible gain of 13079 BTUH, and heat loss of 30,888 BTUH
Submitted: 2 years ago.
Category: HVAC
Expert:  MattR757 replied 2 years ago.

MattR757 :

Based on your square footage I'd estimate a 2.5 ton Heat Pump for system 1 with 10kw of electric auxilliary and a 2 ton Heat Pump for system 2 with 10kw of electric auxilliary.

MattR757 :

Are you splitting the total area by floor or by zone?

MattR757 :

Depending on your location you can undersize one system for stratification (because heat rises) - for example - if you live in the south you might put a slightly smaller unit downstairs as cool air will naturally sink to the lower rooms reducing the actual cooling load - Opposite for northern states where heat load is the primary concern.

MattR757 :

It really is sad how few contractors do the load calculations anymore - The numbers don't lie and it is going to be part of the permit process in many localities soon.

MattR757 :

Your numbers for system 1 would seem to indicate a heat gain of just over 1.5 tons but based on square footage I'd expect more like 2.5 tons

Customer:

I guess we're splitting it by zone. Each unit downstairs will supply approx. half of the downstairs each. Our downstairs floor plan is pretty open. We have another 2 ton heat pump for the upstairs that is still going strong. The bottom floor is the main floor of our house. It contains our master suite. The upstairs contains guest rooms, office and bonus room.

Customer:

We live in WV. According to the manual J book. Summer temp is 81 F. and winter is 4 F. (99% and 1%)

MattR757 :

Ah - elevation - so I wouldn't undersize either system -

MattR757 :

The load calculation - was an online calculator tool? - probably based on manual J which uses weighted average factors for windows, doors and construction materials while the more expensive programs use ASHRAE RLF calculations and base loads on hour by hour factoring which makes the overall load higher

MattR757 :

I can't recommend highly enough the Trane XLi series, As long as it is installed properly.. I'm sure you would be happy with the system. - Just make sure you get the extended warranty even if it costs a little more up front. The indoor fan motor alone is nearly \$900 (my cost) and the control boards run between \$300 and \$600 each

MattR757 :

You have a total of almost 2400 square feet which would push the total load between 4 and 5 tons for cooling - splitting to 2.5 and 1.5 will save tonnage (and therefore operating \$\$) while still covering the expected load

Customer:

The load calculator was based on manual J. It had you enter each room size, walls (and their direction), insulation, windows, doors, etc.

Customer:

I was originally going to go with the 20xli, but after doing more reading was leaning toward the 15xli, Not sure if I really need 2 compressors or even a 2stage compressor. What do you think about single compressor vs 2 stage in a moderate climate.

Customer:

Every HVAC contractor so far has recommended the variable speed air handler.

MattR757 :

Behind the scenes it uses a different method of calculation, although not wrong, manual J can occasionally under-calculate the total load.

MattR757 :

the 20XLi is reliable, but I find that the cost is never really offset by the energy savings - you spend more up front to save money in operating cost over the life of the equipment and never really recover the difference

MattR757 :

in my opinion the 20XLi series is a waste of money

Customer:

before I came across this site I was planning on doing a 2.5 ton on one side and a 2 ton on the other side. I know the 15xli is a little less efficient than the 16xli, but it is also a little cheaper. I'm assuming its parts are a little cheaper also due to it being a single stage compressor. Looks like I'd be able to recover most of the money on the 15xli. Not sure if the higher SEER heat pumps are truly worth the extra money. Do you prefer the 2 stage compressors over the single stage. (last question)

Customer:

Looks like all the XLis have a 12 year warranty on the compressor compared to 10 years for the other trane heat pumps. Should I consider another trane heat pump besides the 15xli? Trane seems to have the better contractors in our area.

MattR757 :

No. In WV you pay around 10 cents per kilowatt for electricity - your system runs - probably around 4000 hours per year (ballpark 2000 for cooling and 2000 for heating) - Not counting electric auxilliary heat (which is the same for any heat pump regardless of SEER) - The difference in operating cost would likely be close to \$150 per year. average life of the system is 12 years so 12x150 is around \$1800 - deduct for efficiency loss over life and you save between \$1200 and \$1500 over a 12 year period.

MattR757 :

I'm guessing that the difference in price is more that \$1200 to upgrade to the higher efficiency system - Plus the additional maintenance and potential repair cost - Again - my opinion

MattR757 :

I used to be one of the sales guys who tried to sell the most efficient system we offered but once I started doing the math it just didn't make sense to me anymore

MattR757 :

I personally sell a lot of the 15's. I work/live in coastal Virginia and I don't usually recommend lower efficiency units unless it is for a rental or commercial property - If you plan on staying in the house for the next 5-10n years I'd stick with the 15XLi

Customer:

two 20xli with new duct work was quoted at \$22,500

Customer:

two 15xli with duct work was quoted 18,200

Customer:

we plan on being here for a long time

Customer:

the duct work is sheet metal insulated on the outside

Customer:

The 16xli was quoted at 20,500

MattR757 :

I'm suprised that the 20's aren't a little higher. Our average here is in the mid \$8000's per system with ductwork, but we have a lot of competition that keeps our rates a little lower than I need them to be. - Honestly, for the 15XLi, the equipment should cost the contractor between \$2000 and \$2500 - add another \$1000 for duct materials - probably 2 men for 2 days to install each system and overhead and profit - The pricing seems fair

MattR757 :

I'd still stay with the 15 -

MattR757 :

The availability of parts for the higher efficiency systems isn't good - even our supply house doesn't stock motors because the demand isn't there

Customer:

Thanks. . I know they have other non XL series (XR...) with higher SEERS. But two year less compressor warranty. Do you rec. staying with the XLi series.

MattR757 :

hmmm. how do I respond

MattR757 :

I have replaced roughly a dozen Trane compressors so far this year and not one of them was on an XL series unit.

Customer:

point taken.

Customer:

variable speed air handler? yes/no This will be my last question. For real this time. Just would like your opinion.

MattR757 :

Trane makes their compressors in Tyler Tx for the XL series units - (I think they still make all of their compressors there) and they take great pride in the reliability

MattR757 :

Yes - definitely - I have been a big fan of variable speed indoor motors since the mid 90's - The difference is indescribable

Customer:

same tonnage as the heat pumps?

MattR757 :

Variable speed blowers might be the best thing to happen for indoor comfort since Mr Carrier sat on a bench in a train station

MattR757 :

yes - for WV you want to match the indoor and outdoor - We only mismatch for humidity issues like very arid climates get a bigger outdoor unit than the indoor because we are more concerned about sensible load

MattR757 :

You want matched units

Customer:

Thanks for taking the time to answer all my questions. Just needed a little reassurance.

MattR757 :

no problem - If you have more questions you can message me and I will be happy to help

MattR757 :

I'm here almost every day

MattR757, HVAC Technician
Category: HVAC
Satisfied Customers: 52
Experience: 18+ Years experience in residential and commercial HVAC service and repair

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