Air Flow Issues

[shanerrs]

I am in the process of purchasing a new house in Toronto Canada. The house is complete renovation and has had a new HVAC system installed. I have some concerns with the Airflow in the system. During my last visit to the house for approximatly 2 hours the tempature on change .5 degree C.

The airflow in the system seems to be low, but I am not expert. I have gotten some quotes from various installers that suggest the CFM is too low for the Furance installed.

The house:
2400 sq ft
2 storey with basment
Second storey is new and all new windows.

The furnace:
Lennex GFU43-24b-070
70,000 BTU
CFM range is 425 - 1020


Any thoughts on this set up?

thanks

[wahoo]

I'm not familiar with that model number, however based on your homes size, you have reason to be concerned. You need to have an experienced HVAC contractor actually test the air flow from your system, and get his recommendations in writing. DO THIS BEFORE YOU CLOSE on this property unless you already plan on possibly fixing this problem with your own money! I'd not recommend the same contractor who installed the equipment however.

[shanerrs]

We did have the CFM tested per register and the average was around 50 cfm per register.

We do have 2 register per room in most cases. IE bedrooms, kitchen etc.

the house is 2400 sq ft including the basement, with main floor and the second floor total of 1700.

The A/C unit is a 2 ton unit.

thanks for any help.

[dash]

Two tons ,so around 800 cfms for cooling,furnace range is over 1000 cfms.

Sounds okay unless the duct system is too small/restrictive.

How was the cfm tested,type of instrument?

What did the total cfm add up to??


Has anyone done a Load Calculation to see what size system is needed for heating and for cooling?Thinking that is the next step you'll need to take.

[shanerrs]

The cfm at each register was tested with a digital cfm meter.

Total CFm added to approximatly 900 cfm. i was not present for this testing thus only have a approximate.

Duct system is all new, and design calls for 5inch ducts through out.

[udarrell]

The cfm at each register was tested with a digital cfm meter.

Total CFm added to approximatly 900 cfm. i was not present for this testing thus only have a approximate.

Duct system is all new, and design calls for 5-inch (metal?) ducts through out.

Well, that sounds okay as far as the total CFM goes.

However, with only 50-CFM per supply air grille that would require a properly selected diffuser or it may not produce the requisite velocity & throw.

They would need to use a Hart&Cooley or other small supply air register with only around an Ak sq.ft. area of around only .14-sq.ft.

At 50-CFM / by .14-sq.ft. = 357-FPM velocity so it would be necessary to carefully select registers for the proper throw & placement in each room.

A 5" duct 5X's 5=25X's .7854= 19.635-sq.ins., / 144 = .1363541-sq.ft. | 50-CFM /.1363541-sq.ft.= 366.6-FPM velocity.
My software says: a 25' run with two 90-ells is 0.02" FR. Velocity 367-FPM; @ a 100' run it's 0.06" Friction Rate.

With two registers per room, nearly everything apparently might be A-Okay. - Darrell

[beenthere]

Was that 900 CFM in heating or cooling mode.

[udarrell]

My post was pointed toward the 2-Ton cooling mode.
Actually, 800-CFM is most used for 2-Ton of cooling, but that test may have been done with a dry coil? Which would be around 850-CFM with a wet coil.

Pay attention to Dash & beenthere's posts, & get all that definitive information from the contractor. You will also want the proper airflow for heating.

Did the installer do a manual D?
It is the proper way to design the duct system to fit the cooling & heating airflow demands with the existing air handler.

http://www.udarrell.com/duct_system_chart.pdf - Darrell

[johnt2_2002]

that furnace is a basic high-eff. furnace. not too bad for a builders furnace. a lot of newer homes ive come across in the GTA have that model furnace. but as far as the ductwork goes coming off the main trunk..ive seen lots of restrictions where the builder would put multiple 90's together to go over beams and odd designs as they go upstairs..hopefully, the duct design is ok.

oh, and check the furnace filter

[shanerrs]

Hi All,

Thanks for all the help, I really appreciate it.

I am now looking for a "Non Biased" inspection in the GTA. Thus someone that is not in sales avalible to do a in home inspetion. Does anybody have a suggestiong of a HVAC spesilist inthe Toronto Area.

The CFM levels were done during cooling, with the vents closed in the basement - As per the Sellers HVAC guy said is the proper way to do the testing.

shane

[beenthere]

The sellers HVAC guy works for the seller. Not you.

If you had 900CFM. On a 2 ton, with the A/C running. The seller has probably had the same problem.

[shanerrs]

the seller has never lived there. So we have not true real life experience in the house. The house was a bungalo and now is a two storey reno.

Thus we are going on theroy only and are speculating if there are issues or not.