What size HVAC Unit for a 2,400 sf house?

[hjohnston]

I'm installing a new condenser, coil and furnace. I have a 2,400sf home and currently have a 4 ton system in there, but have been told by the HVAC company that I should put in a 5 ton system. Is that okay?

Also, I'm getting the total tax credit just installing the A/C, so was considering the 80% AFUE furnace, but also considering the 95% AFUE furnace. It's more $, is it worth it?

THANK YOU!!

[Cold Feet]

I'm installing a new condenser, coil and furnace. I have a 2,400sf home and currently have a 4 ton system in there, but have been told by the HVAC company that I should put in a 5 ton system. Is that okay?

Your contractor needs to do a Manual J load calculation to determine your heat loss and heat gain figures. These indicate how large a AC and furnace you need. If your contractor hasn't done this, he's either guessing about what size AC to install or is trying to clear out whatever he can get cheap.

Also, I'm getting the total tax credit just installing the A/C, so was considering the 80% AFUE furnace, but also considering the 95% AFUE furnace.

Depends on your house's heat loss and length of the heating season.

[hjohnston]

Thank you! I live in Dallas...not sure about the home's heat loss, but it can get pretty cold down here, but not for long...

[Daltex]

Were you having problems with the 4 ton keeping up with the cooling?

Remove pricing as per forum rules.

[Integrity Aire]

this ones gonna be great.....

[hjohnston]

Thanks - didn't now you couldn't post $$! No, the 4 ton is not having trouble keeping up.

[Daltex]

If 4 ton unit was keeping up then the only thing you will do by increasing it to 5 tons is the decrease in humidity removal. The 4 ton may be perfect or maybe oversized. Run a load calculation and see before you spend the money on a new system.

I'd go for a heat pump with a 80% furnace as backup heat. Cost a very small amount more but will save alot of expense. Also stay with a variable speed blower.

Find a new AC company as the company that quoted your new system is already cutting corners it seems to me.

[pstu]

I'm installing a new condenser, coil and furnace. I have a 2,400sf home and currently have a 4 ton system in there, but have been told by the HVAC company that I should put in a 5 ton system. Is that okay?

Also, I'm getting the total tax credit just installing the A/C, so was considering the 80% AFUE furnace, but also considering the 95% AFUE furnace. It's more $, is it worth it?

THANK YOU!!

Just wondering, did the AC guy say it would be OK to increase duct air speed by 25%? I have looked at ACCA Manual D and it does not seem to support that you can casually do that. If some testing was done to establish the duct system was that much over-designed, or if he proposed to change ductwork for higher capacity, that would be different.

Assuming he did not, as a homeowner I *might* consider this yet another reason to use a pro who adheres better to ACCA methods.

Best of luck -- Pstu

[catmanacman]

did the company tell you they would upgrade you to a 5 ton and make it cool a lot faster

[Ti Llaves]

Just wondering, did the AC guy say it would be OK to increase duct air speed by 25%? I have looked at ACCA Manual D and it does not seem to support that you can casually do that. If some testing was done to establish the duct system was that much over-designed, or if he proposed to change ductwork for higher capacity, that would be different.

Assuming he did not, as a homeowner I *might* consider this yet another reason to use a pro who adheres better to ACCA methods.

Best of luck -- Pstu

You are correct. When it come to installing a variable speed blower it's accentual that the duct work is compatible.

[Ti Llaves]

If 4 ton unit was keeping up then the only thing you will do by increasing it to 5 tons is the decrease in humidity removal. The 4 ton may be perfect or maybe oversized. Run a load calculation and see before you spend the money on a new system.

I'd go for a heat pump with a 80% furnace as backup heat. Cost a very small amount more but will save alot of expense. Also stay with a variable speed blower.

Find a new AC company as the company that quoted your new system is already cutting corners it seems to me.

Good question.

[heaterman]

Make double sure there is a certificate to go along with that 5 Ton AC system that qualifies for the tax credit. I doubt it.

[Ti Llaves]

Thanks - didn't now you couldn't post $$! No, the 4 ton is not having trouble keeping up.

The performance in conducting a manual j can be questionable. It depends on the age of the home and how tight it is, oversize is far worst than under sizing an a/c system. Conducting a manual j is effective in new construction. At lease in new construction you know all the installation factors in order to make a true calculation, that's were the use of performing a manual j is most effective.

[jimj]

The performance in conducting a manual j can be questionable. At lease in new construction you know all the installation factors in order to make a true calculation, that's were the use of performing a manual j is most effective.

Sorry I have to disagree. Done correctly it will work EVERY TIME, if the home is within manual j parameters.

[Twilly]

Twilli says 2XL

[Cold Feet]

The performance in conducting a manual j can be questionable. It depends on the age of the home and how tight it is, oversize is far worst than under sizing an a/c system. Conducting a manual j is effective in new construction. At lease in new construction you know all the installation factors in order to make a true calculation, that's were the use of performing a manual j is most effective.

Manual J works as long as you're not too lazy to find out exactly how the building is constructed. It's harder to find out how an older building has been built but that's not a fault of Manual J.

No algorithm or formula works right if its applied to inaccurate data.

[heaterman]

The performance in conducting a manual j can be questionable. It depends on the age of the home and how tight it is, oversize is far worst than under sizing an a/c system. Conducting a manual j is effective in new construction. At lease in new construction you know all the installation factors in order to make a true calculation, that's were the use of performing a manual j is most effective.

Wrong answer Scooter. Granted, if you get a slacker who is trying to hand you a line to sell you, then the results may be bad, face it anyone can fudge numbers to get what they want. Garbage in, garbage out. Doing a Manual J IS THE ONLY WAY to know what your needs are, period, end of statement, anyone else who tells you differently is full of something vile.

[hvaclover]

Wrong answer Scooter. Granted, if you get a slacker who is trying to hand you a line to sell you, then the results may be bad, face it anyone can fudge numbers to get what they want. Garbage in, garbage out. Doing a Manual J IS THE ONLY WAY to know what your needs are, period, end of statement, anyone else who tells you differently is full of something vile.

No sarcasm intended, how do you find out what's in the walls? That is my biggest gripe with man J. It has been suggested that removing outlet covers and light switch covers let you see what is in the walls. Have yet to have anybody tell me that they could determine insulation value in outer walls using this method.

To day if I suspect a poorly insulated wall I will measure the temp diff between the inner and outer wall surfaces. It gives me a lot of info cause I can compare it to other homes in the area.

[jimj]

No sarcasm intended, how do you find out what's in the walls? That is my biggest gripe with man J. It has been suggested that removing outlet covers and light switch covers let you see what is in the walls. Have yet to have anybody tell me that they could determine insulation value in outer walls using this method.

To day if I suspect a poorly insulated wall I will measure the temp diff between the inner and outer wall surfaces. It gives me a lot of info cause I can compare it to other homes in the area.

NCI has a procedure for telling just that, however it is proprietary to them and there members so I will not divulge it here.
I will say your on the rite path checking temp differentials, there is a little more to it than that.

[Daltex]

No sarcasm intended, how do you find out what's in the walls? That is my biggest gripe with man J. It has been suggested that removing outlet covers and light switch covers let you see what is in the walls. Have yet to have anybody tell me that they could determine insulation value in outer walls using this method.

To day if I suspect a poorly insulated wall I will measure the temp diff between the inner and outer wall surfaces. It gives me a lot of info cause I can compare it to other homes in the area.

Sometimes in an existing home, you can't easily get an accurate R factor of the wall insulation. Even if you removed a piece of drywall to see what's behind it, you may miss some settling of the insulation or other factors that play a role.

The wall insulation doesn't play as major of a factor as other aspects of the build for example size, type and location of windows.

I'd recommend using the best guestimate of the unknows, such as the IR temp reading you mentioned, and then once the man. J and S are complete, compair your results with what the homeowners experience was with the old unit. The problem lies in the fact that if the old unit (per the HO) wasn't keeping up with the heat gain- It may not be that the unit was undersized.

If the HO says the unit was fine, I sure wouldn't upsize it as long as his stat setpoint was reasonable.