# System Design



## Justin Jarrett (Feb 22, 2014)

Hello, I'm an HVAC/R contractor new to this site. I need some quick advice and hopefully somebody can help me out. I normally operate in the city on smaller row homes. But I have a house in the subburbs I'm trying to bid on. It's for a couple of real estate investors/ flippers. It's a 2000 sq. ft, older two-story . Mostly stone and brick. They are turning the 3rd floor addict into two bedrooms. (adding 500 sq. ft.). Currently the house has a Hydronic Nat. gas. boiler. A 140kbtu input 80% weil-mcclane. Looks like its in good shape. Maybe 7 years old. NO A/C in the house. They want AC installed.. My thoughts are to switch over to forced hot air, since I would be installing ducted A/C in the house anyway. 
As for cooling. In the city I normally estimate 1 ton of refrigeration per 400 sq.ft. since the homes are usually pretty old. I know newer homes you can go to 500 and up. This house is pretty old, not well insulated (although the addict will be insulated well after rehab). At that rate per btu, the house would need 6.2 tons of A/C. Seems like alot to me. Can I even get a 6 ton residential unit? I thought they only go to 5. Could I get away with a 5 ton? 
As for heat, The biggest unit I can get is 110kbtu output. (Goodman)
will that handle 2500 sq.ft? the chart I have for this area says 2000-2500 sq ft. needs 102kbtu output. (philadelphia area). I think the 110kbtu could handle it, but I'm worried about the cooling. I dont think 5 tons would be enough. Does anybody have any thoughts on this?
I'm trying to avoid doing a full load calculation on the house ( i usually pay an engineer to do it), I only had a short window at the residence and I want to get these guys a quote fast. But I can't even figure out the design yet

I also considered installing two systems. A 60kbtu output furnace for the first floor(1000ft2), and a 60kbtu output furnace for the second floor (1000ft2) and third floor addict (500ft2). The first floor would have 2.5 ton evap and 2nd, 3rd floor unit would have a 3.5 ton evap. 

I'd prefer a one unit system and I'm sure they would too. But I'm not sure I can make a one unit system work. Could I throw a 110kbtu output furnace and 5 ton ac in there? Any advice would be appreciated. Thanks


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## Patrick Eubanks (Mar 2, 2012)

*Load*

I don't think Im allowed to post here as I don't have a professional status on this site but I will anyway since no one else has. You need to run a load first and foremost. Here in NC local codes require either a zone system or multiple units for multiple floors. I am pretty sure your load would show that 400 sf/ton is oversized on the AC side of the equation if using conventional AC. Check your local codes and see if two units are required. (I bet they are)


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## beenthere (May 30, 2009)

400 sq ft per ton in phiily is nuts. Thats over sized. 

Do a load calc, and you'll find you need a lot smaller unit then you think. 2500 sq ft house in philly area, 80,000 BTU input 95% efficient furnace at most.


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## michaelhaines (Mar 24, 2014)

*System design options*

You may want to consider leaving the 7 year old boiler and installing a heat pump system so they can choose which heating source to use based on ambient conditions and your local electric and gas rates. This way they have two heating sources in case one fails. Definitely need to do a load calc. Consider the Rheem DesignStar for for now as it is free and very easy to use. Just put in the address and it is calculates based on the home. 

I think the load calc will come in at around 5 tons. I would normally say to consider zoning the floors since you are retro-fitting new ducts. if they are investors they may pass on this extra-cost option but I would at least submit the idea as I've been surprised by some investors willing to impart some extra comfort benefit into the value of the property. 5.0 tons is the largest residential system you can buy.

Best of luck to you


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## airtrackinc (Feb 12, 2014)

Yes, as a rule of them you can stick with 110K two stage heating with 3 Ton cooling for all house. just matter of getting proper air flow around the house now.


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## beenthere (May 30, 2009)

airtrackinc said:


> Yes, as a rule of them you can stick with 110K two stage heating with 3 Ton cooling for all house. just matter of getting proper air flow around the house now.


Over sized for the OPs location.


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## hvaclounge.com (Apr 15, 2014)

Patrick Eubanks said:


> I don't think Im allowed to post here as I don't have a professional status on this site but I will anyway since no one else has. You need to run a load first and foremost. Here in NC local codes require either a zone system or multiple units for multiple floors. I am pretty sure your load would show that 400 sf/ton is oversized on the AC side of the equation if using conventional AC. Check your local codes and see if two units are required. (I bet they are)


Hey Patrick, just wanted to chime in and say I think you are right. Also, it's interesting how some places local codes require zone systems and some don't. I wonder how they decide this.


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## SUREFIRE (Apr 21, 2014)

A proper Manual J is always the way to go, but you are almost definitely oversized. I think if you did a manual J, you'd find that a 5 ton would suffice...and you can use a general rule of thumb of 600 sq ft. / ton as opposed to 400 which I would use in commercial applications.

Although I agree to keep the boiler, you can look into Rheem furnaces they have 140,000 BTU...not my favorite brand, but it's an option. If you're keeping the boiler you don't have to get a heat pump either. If you need to keep the cost down a hot water coil will do.

-Jason 
SUREFIRE Mechanical- Long Island Air Conditioning Repair Experts


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