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View Full Version : Rule of thumb - tonage>sq ft of below grade basement.

alecmcmahon
04-26-2011, 11:15 PM
What is the general rule of thumb when it comes to X amount of tons to square footage of home / basement.

I know that you can roughly use 500 sq foot per ton if your house is drafty and old construction

But what about a basement that is about 80% below grade ? If the basement is 1000 sq feet approx. do you count that as 500/500=2 tons? or give it 1 ton? or even half?

example:

1950s ranch , central nj... Summers can top 100 degrees, typically 80-90 all summer long, can be very humid,but varies.

Poor insulation in walls, maybe 2 inch thick, single pane drafty wooden windows, poorly insulated attic, etc. etc.

main level - 1000 sq ft
basement 1000 sq ft

Am i correct in assuming a rough estimate should be about 3 tons of cooling for this home?

04-26-2011, 11:49 PM
Do you have a car with a carburetor? That's about how relevant rule of thumb is in the HVAC industry today. Real A/C techs do load calculations. Smart homeowners have energy audits done so they can use the least amount of increasingly expensive energy as possible. If you do not believe me, do some reading around here about the problems others have when they do not pay attention to these things. Assuming anything with something that cost this much to install and run is crazy. It's not like a car you can just trade in in a couple of years if it doesn't work out for you.

dan sw fl
04-27-2011, 05:55 AM
What is the general rule of thumb when it comes to X amount of tons to square footage of home / basement.

I know that you can roughly use 500 sq foot per ton if your house is drafty and old construction

But what about a basement that is about 80% below grade ? If the basement is 1000 sq feet approx. do you count that as 500/500=2 tons?
example:

1950s ranch , central nj...
Summers can top 100 degrees, typically 80-90 all summer long, can be very humid,but varies.

Poor insulation in walls, maybe 2 inch thick, single pane drafty wooden windows, poorly insulated attic, etc. etc.

main level - 1000 sq ft
basement 1000 sq ft

Am i correct in assuming a rough estimate should be about 3 tons of cooling for this home?

3 tons is IN THE BALL PARK.

Variable speed AHU and 2 stage compressor should be considered.

Air distribution is important so the loads for each area need to be determined.

BaldLoonie
04-27-2011, 06:18 AM
The basement adds virtually nothing to cooling needs of the home. An accurate load calc should be done. 3 tons for 1000 sq ft sounds very high and can lead to humidity issues due to short cycling. So before you do anything, either you or a dealer measure and crunch the numbers before you regret it. Clikc the HVAC Calc tab above, \$50 is worth it.

cmp240
04-27-2011, 08:20 AM
Roughly 500sq ft per ton is right,roughly is right,need to hve a load calc done,chk duct work,rtn ducts,airflow,etc.etc. call a pro,hav it done right the 1st time,good luck

TwincamDave
04-27-2011, 09:58 AM
I would tend to undersize by 1/2 ton after your load calcs are done only to get more run time to properly dehumdify. Virtually no load on the basement you just want to dry it out.

alecmcmahon
04-27-2011, 10:11 AM
here is my hvac calc that I did.

2 tons seems like it would be too small? thought for sure a 2.5 ton would suffice.

http://farm6.static.flickr.com/5108/5661423820_d310d7afe6_b.jpg

udarrell
04-27-2011, 10:29 AM
For better humidity control with single speed A/C, I'd get a differential 1-3-F with half degree incrementals to get ample length run cycles.

All older RM stats had cooling anticipator to produce a little heat & kick them back on quicker so room temp would stay real close to set point.

I want long efficient runtimes achieving a higher SEER & coming on at say 77-F off at 75 or 74-F, etc.

A 2 or 3 degree swing in the human comfort zone is not going to kill you! You'll actually be more comfortable with the better controlled lower humidity!

That is what I'd have to have...
Here is one, believe there are others.

http://www.amazon.com/Robertshaw-RS5110-Programmable-Thermostat-Heat/product-reviews/B0018M47LW

alecmcmahon
04-27-2011, 11:21 AM
updated report, forgot to add my porch . which we never used for living space cause it was too damn hot. lol

got 2.5 tons now.

http://farm6.static.flickr.com/5108/5661603846_e81e6dd090_o.png

arc8
04-27-2011, 12:26 PM
updated report, forgot to add my porch . which we never used for living space cause it was too damn hot. lol

got 2.5 tons now.

http://farm6.static.flickr.com/5108/5661603846_e81e6dd090_o.png

Can a 2.5 ton really pull out 26,162 from your house on the hottest days?

Kevin O'Neill
04-27-2011, 12:32 PM
If the system is installed correctly, heck yes!

alecmcmahon
04-27-2011, 12:39 PM
Can a 2.5 ton really pull out 26,162 from your house on the hottest days?

I hope so ? I set the summer temp at 105 degrees , that's pretty much as hot as it can get. And my main floor living space is just under 1000 sq ft, basement is the same sq ft but all below grade, so much cooling shouldn't be nessasary

1 ton of cooling = 12,000 BTUH

12,000+12,000+6,000 =30,000 BTUH
(1ton)+(1ton)+(.5ton) = 2.5 tons

wahoo
04-27-2011, 01:12 PM
Alec, I think you'll find the actual BTU cooling output is lower than the 30k you estimated. In actual use and matched up, the output is probably 27 to 28k total. And this will vary depending on actual airflow/ductwork installed. Just checked a 16 SEER, 2 1/2 ton and the total cooling output was 28.8 to 29k.

arc8
04-27-2011, 01:14 PM
I hope so ? I set the summer temp at 105 degrees , that's pretty much as hot as it can get. And my main floor living space is just under 1000 sq ft, basement is the same sq ft but all below grade, so much cooling shouldn't be nessasary

1 ton of cooling = 12,000 BTUH

12,000+12,000+6,000 =30,000 BTUH
(1ton)+(1ton)+(.5ton) = 2.5 tons

Not exactly.

It depends, what your RA (inside temp) temp going to be?
It depends on what your Sensible Heat Ratio will be; you are in a Hot and Humid climate!

I say look at the equipment that you'll be choosing!!

ampulman
04-27-2011, 01:33 PM
here is my hvac calc that I did.

2 tons seems like it would be too small? thought for sure a 2.5 ton would suffice.

http://farm6.static.flickr.com/5108/5661423820_d310d7afe6_b.jpg

I'm in S. Jersey, near Philly, where design temps are 90/14. I'd be curious where you're located. Highest summer design temp in HVAC-Calc is 91 (yours is 96).

Some have stated that the program already builds a safety factor.

P.S., I can't recall having a temp of 100 or greater in at least the last 23 years.

Amp

KCA
04-27-2011, 01:34 PM
Remember that he cranked up the summer design temperature. I haven't checked, but I suspect that the actual summer design temperature is more like 95F (or less) for NJ. Depending on how much adjustment was made, there may be quite a bit of margin in those cooling loads.

Edit: I mean compared to the 105F used. That 96F value might have been bumped up too. Here in central VA, I used 95F. I think that the code had 90F listed for my location.

alecmcmahon
04-27-2011, 02:06 PM
Im in Woodbridge NJ, Central. It did top 100 degrees a few times last summer, so I bumped it up to 105 to be safe on them blistering days, The default for my area was 89 degrees.... which cant be right, alot of summers days are in the upper 90's if not topping 100 degrees.

If I decide to cool my porch ( 3 season porch type of deal )im at roughly 29,000 BTUH

without cooling my porch im at about 22,000 BTUH

Im really torn between the 2 ton and 2.5 ton, will steping the half ton up really kill me with not pulling out humidity?

I planned on going with a 13 seer 2.5 ton LUXAIRE unit, i'll try to look up to see what the btuh specs are.

Kevin O'Neill
04-27-2011, 02:16 PM
Im in Woodbridge NJ, Central. It did top 100 degrees a few times last summer, so I bumped it up to 105 to be safe on them blistering days, but the im pretty sure the 96 was default when i loaded my area in

If I decide to cool my porch ( 3 season porch type of deal )im at roughly 29,000 BTUH

without cooling my porch im at about 22,000 BTUH

Im really torn between the 2 ton and 2.5 ton, will steping the half ton up really kill me with not pulling out humidity?

I planned on going with a 13 seer 2.5 ton LUXAIRE unit, i'll try to look up to see what the btuh specs are.

Bumping it up to be safe is a really bad idea, for a few hours on a couple of days. We went up to 100 a couple of hours last year, but I design for 90 degrees, and I am south of you. It is a shame you an't find a contractor who will do this for you.

KCA
04-27-2011, 02:17 PM
It's it best to use what is in the code or at most bump it up by 5F. Although the temperature may exceed this value for a couple hours out of the summer, it is no big deal. All it means is that your indoor temp may be at say 74F instead of 72F. It might even keep up anyway as there is some fudge factor already built in to the code.

It might be out of your budget, but a 2-stage unit might help. In my case, the calculated load was about 2.5 ton or so. The old AC unit was 3 ton. I went with a 2-stage, 3 ton unit (2 ton on low, 3 ton on high). So far, it works well.

alecmcmahon
04-27-2011, 02:30 PM
Going back to the default temperature #'s it puts me at 24,000 and change for my heat gain

So i guess a 2 ton unit is what is needed.

Will there be different BTU/Hour outputs depending on seer and manufacture of the unit?

Will it be 12,000 btu/hr? or +/- ?

again, i'll probably go with luxaire 2ton 13 seer, now.

alecmcmahon
04-27-2011, 02:54 PM
Also, just checked my neighbors unit, he has the same exact house setup as me.

the model on his unit is:

HABC-F030SD

does the " 30 " stand for 30,000 BTUH ?

= 2.5 tons?

alecmcmahon
04-27-2011, 04:36 PM
Also, just checked my neighbors unit, he has the same exact house setup as me.

the model on his unit is:

HABC-F030SD

does the " 30 " stand for 30,000 BTUH ?

= 2.5 tons?

Just spoke to my neighbor, he said that he wishes they had at least a half ton more in the summer time cause during the worst days it doesnt keep up.

udarrell
04-27-2011, 04:39 PM
I'm in S. Jersey, near Philly, where design temps are 90/14. I'd be curious where you're located. Highest summer design temp in HVAC-Calc is 91 (yours is 96).

Some have stated that the program already builds a safety factor.

P.S., I can't recall having a temp of 100 or greater in at least the last 23 years.

Amp

Summer 2.5% design dry bulb; New Brunswick. NJ is on the south end of Newark down toward Trenton.

Trenton is 88-DB & 74 WB or about 50% RH.

Newark, is 91-DB; 73-WB near 43% RH; it is usually hotter in a large city like Newark then in a smaller ones, or in outlying suburbs.

I would not jump it to 96-F, or at all.
also, you're using 72-F indoors; I would not go below 75-F indoors; 91 - 75 is 16 degree differential; 105 is way out of line.

You use the Design figures, you don't bump those figures up.

You can always reduce air infiltration & do half a dozen other things to reduce the heat-gain...

udarrell
04-27-2011, 04:54 PM
Just spoke to my neighbor, he said that he wishes they had at least a half ton more in the summer time cause during the worst days it doesnt keep up.

You can't go by what someone else's same tonnage & same home design is doing; because due to many factors it may be delivering a fair amount less than 2-ton of heat absorption & transfer to the outdoors. BTUH can be okay; but I'd also check for return air being pulled from an unconditioned area; it's common.

If I were there, I'd ballpark check the actual delivered BTUH by his system; also check how well his home is effectively rejecting the rate of heat-gain.

Those difference between HVAC systems,& identical looking homes can be very different.

Do what you want to do; but you won't cook even on those extra hot days; & it won't be extremely oversized for 90% of the cooling days.

ampulman
04-27-2011, 07:45 PM
Just spoke to my neighbor, he said that he wishes they had at least a half ton more in the summer time cause during the worst days it doesnt keep up.

Did he inherit the a/c? IF so, it may not have been designed to his 'indoor' specification. So, if he's 'bumping up' his thermostat (beyond what the unit was designed for), it may not keep up.

BTW, does your neighbor's house face the sun, the same as yours? What about shading, proximity of other buildings, etc.? If not, may change the how picture.

Amp

genduct
04-27-2011, 08:24 PM
Your latent load is only 10% of the tota in Central Jersey? HUMMMMM
When you really select your unit You'll ( or someone who understands this) need to look at the extended info to figure out what you really need NOT THE THUMB METHOD

beenthere
04-27-2011, 08:39 PM
Im in Woodbridge NJ, Central. It did top 100 degrees a few times last summer, so I bumped it up to 105 to be safe on them blistering days, The default for my area was 89 degrees.... which cant be right, alot of summers days are in the upper 90's if not topping 100 degrees.

If I decide to cool my porch ( 3 season porch type of deal )im at roughly 29,000 BTUH

without cooling my porch im at about 22,000 BTUH

Im really torn between the 2 ton and 2.5 ton, will steping the half ton up really kill me with not pulling out humidity?

I planned on going with a 13 seer 2.5 ton LUXAIRE unit, i'll try to look up to see what the btuh specs are.

If youn size based on those few days it was over 100, then you will have to set your thermostat that much lower for majority of the summer, just to try and keep the humidity down.

Don't fudge, you'll regret it.

sktn77a
04-27-2011, 08:49 PM
Basements generally have much lower temperature fluctuations that above-ground spaces. This would translate into a lower heating/cooling requirement for a given square footage. I'm not sure how HVAC-Calc or other load calculators figure basement loads - just be sure they aren't treating it as an above-ground space.

alecmcmahon
04-27-2011, 10:11 PM
Did he inherit the a/c? IF so, it may not have been designed to his 'indoor' specification. So, if he's 'bumping up' his thermostat (beyond what the unit was designed for), it may not keep up.

BTW, does your neighbor's house face the sun, the same as yours? What about shading, proximity of other buildings, etc.? If not, may change the how picture.

Amp

same exact layout, same house, built at same time, side by side... we both get the same sun.

he had his unit pro installed about 5 years ago, 2.5 ton luxaire, he says in the summer time it does have a hard time keeping up and would def. put in a 3 ton if he had known.

arc8
04-27-2011, 10:19 PM
same exact layout, same house, built at same time, side by side... we both get the same sun.

he had his unit pro installed about 5 years ago, 2.5 ton luxaire, he says in the summer time it does have a hard time keeping up and would def. put in a 3 ton if he had known.

Perhaps it has something to do with their furnace (blower:CFM).

beenthere
04-28-2011, 05:13 AM
same exact layout, same house, built at same time, side by side... we both get the same sun.

he had his unit pro installed about 5 years ago, 2.5 ton luxaire, he says in the summer time it does have a hard time keeping up and would def. put in a 3 ton if he had known.

What is a hard time keeping up. When we have our 98° days here, my A/C will run non stop for 6 hours or more to hold 72. Shut off for 10 minutes or so and then run again for 4 to 6 hours.

Duct work sizing is probably more of his problem then unit sizing is.

dan sw fl
04-28-2011, 06:45 AM
I hope so ? I set the summer temp at 105 degrees , that's pretty much as hot as it can get. And my main floor living space is just under 1000 sq ft, basement is the same sq ft but all below grade, so much cooling shouldn't be nessasary

1 ton of cooling = 12,000 BTUH

12,000+12,000+6,000 =30,000 BTUH
(1ton)+(1ton)+(.5ton) = 2.5 tons

Don't forget about both ManualS S & D AND
derating perfomance to account
for the very low thermostat setting and high outside temperature.

:whistle:
AND some one must check it, so that it is Reasonable

dan sw fl
04-28-2011, 07:25 AM
Im in Woodbridge NJ, Central. It did top 100 degrees a few times last summer, so I bumped it up to 105 to be safe on them blistering days, The default for my area was 89 degrees.... which cant be right, alot of summers days are in the upper 90's if not topping 100 degrees.

I planned on going with a 13 seer 2.5 ton LUXAIRE unit, i'll try to look up to see what the btuh specs are.

Criteria - Step ONE ...
Reasonable sizing - 92'F - 74'F = 18' F ........ Conventional Practice

Stretch ........... - 96'F - 74'F = 22' F

Owner ............. - 96'F - 72'F = 24' F
1.5 * reasonable dT ........................

Unrealistic ......... - 105'F- 72'F = 33'F
ABSURD ... nearly 2X differential temperature in Conventional Practice

George2
04-28-2011, 07:48 AM
Is the furnace and ductwork in the basement or in the attic?

Your attic insulation, which you said is poor, is the easiest and cheapest improvement you can make.

Hopefully the attic has the proper ventilation.

That should be done to improve your comfort and reduce your utilities.

A 2 ton should run away with it.

alecmcmahon
04-28-2011, 08:40 AM
What is a hard time keeping up. When we have our 98° days here, my A/C will run non stop for 6 hours or more to hold 72. Shut off for 10 minutes or so and then run again for 4 to 6 hours.

Duct work sizing is probably more of his problem then unit sizing is.

when he said hard time keeping up he meant it would run all day long and not reach set point. If it was set for 72, he'd be lucky to get it below 76-78

Is the furnace and ductwork in the basement or in the attic?

Your attic insulation, which you said is poor, is the easiest and cheapest improvement you can make.

Hopefully the attic has the proper ventilation.

That should be done to improve your comfort and reduce your utilities.

A 2 ton should run away with it.

Attic.

udarrell
04-28-2011, 08:43 AM
Is the furnace and ductwork in the basement or in the attic?

Your attic insulation, which you said is poor, is the easiest and cheapest improvement you can make.

Hopefully the attic has the proper ventilation.

That should be done to improve your comfort and reduce your utilities.

A 2 ton should run away with it.

Listen to George2; you are focusing like a laser on the BTUH Rating of the condenser, that is only one factor of a dozen that determines what the heat-gain will be & how effectively the entire H-VAC system functions.

If you want your home to get to 72*F on the hottest day of the year then have a thorough home audit & do the scores of things that will bring BOTH heat-gain & heat-loss down to a minimum.

We have homes here in SW WI that are 2400-sf being cooled effectively with 2-Ton units. Our summer design is just a few degrees lower than yours.

I did an energy audit on a 900-sf home next door to me & used 95-db 75-db 20-F sensible differential & got a hair above 14,000-BTUH; without human & appliance loads. Summer Design @ 2.5% Madison, WI area is 88-db 73-wb

It has a 1.5-Ton, it's low on refrigerant & dangerously low on airflow.

Cooling only requires 600-cfm, but heating requires 1200-cfm for its Oil heating Thermo Pride furnace; this is a dangerous situation that has to be addressed ASAP; but hasn't been since 2005...:whistle:

Yes, it runs all the time even in moderate weather, & most would say it needs a bigger condenser tonnage; HOGWASH! Do everything right & you'll learn what a 1.5 or a 2-Ton is capable of cooling.

I cool perfectly on the hottest days over 750-sf with a Half-Ton window unit (1500-sf per/ton) using a 24" fan to circulate it through all the rooms & back to the A/C.

A 1937 farm home NO energy audit or other work performed; 13 old windows & 2 old partial glass doors.

Focus big-time on a properly sized & sealed duct system & airflow efficiencies; then charge it using both superheat & subcooling for comparisons... :cheers:

KCA
04-28-2011, 09:01 AM
The nice thing about air sealing and adding insulation is that not only can it save money by allowing a smaller unit, but it also saves on heating/cooling costs 24/7 for the life of the house. Not only that, but it can make the temperatures more even and you can gain comfort.

On our '68 house, there was only a small amout of loose fiberglass in the attic (maybe 5" and other places had even less). After the 1st winter, we added a layer of R30 on top and worked to seal some gaps. We saw the winter usage drop by around 20%. Also, we have a 2-zone system and usually don't heat the upstairs much (bedrooms). Before adding insulation, you could barely stand to sit on the bottom of the stairs as you got a pretty good breeze with the cold air falling down. After adding the insulation, the upstairs is within a couple of degrees of downstairs even when the heat is not on up there. We also had just an electric furnace for heat (\$\$\$) plus AC. I just took that out and replaced with a nice 2-stage heat pump (should really save some money).

alecmcmahon
04-28-2011, 09:14 AM
Thanks guys, looks like i'll be stick in the 2 ton/2.5 ton range.

Went over the report again, made sure all my details were correct.

http://farm6.static.flickr.com/5185/5664177315_57b5b0af23_o.png

Ron
04-28-2011, 11:13 AM
Your opening post stated poorly insulated attic, single pane windows. Put your money into those two things and you'll keep the system smaller making it less expensive to install and operate. Get a pro in there to evaluate the duct system to make sure you can move the correct amount of air for the equipment.

In my neighborhood I have replaced 2.5 ton a/c with 1.5 ton and had no complaints. That reduction in the system sized it to the heat gain and also made it a better operation in terms of air flow with the inadequate return duct built in to the house. When you describe your house you describe my house in terms of sq.ft. The basement here are more like 4 ft. each above/below grade. Windows have been replaced with double pane/vinyl. Attic added r-25 on top of the original r-19.

glennac
04-28-2011, 06:27 PM
updated report, forgot to add my porch . which we never used for living space cause it was too damn hot. lol

got 2.5 tons now.

You have to be kidding. I put a 1 1/2 ton HP in a 1200 ft2 basement in GA and it never got hot or cold and ran about right. Since they don't have "basements" in FL much less southern FL I can't see you using any more on a basement and less if you live in a cooler climate. Thank you very much.

alecmcmahon
04-28-2011, 06:32 PM
You have to be kidding. I put a 1 1/2 ton HP in a 1200 ft2 basement in GA and it never got hot or cold and ran about right. Since they don't have "basements" in FL much less southern FL I can't see you using any more on a basement and less if you live in a cooler climate. Thank you very much.

Just going by what the numbers say.

And taking a walk down my street, looking at the same or simalar sized houses, everybody has a 2.5 or 3 ton unit.

or was every unit on the street installed incorrectly?

http://farm6.static.flickr.com/5185/5664177315_57b5b0af23_o.png

Kevin O'Neill
04-28-2011, 07:36 PM
Just going by what the numbers say.

And taking a walk down my street, looking at the same or simalar sized houses, everybody has a 2.5 or 3 ton unit.

or was every unit on the street installed incorrectly?
]

Most likely. Improper sizing is very common, unfortunately.

glennac
04-28-2011, 07:50 PM
Just going by what the numbers say.

And taking a walk down my street, looking at the same or simalar sized houses, everybody has a 2.5 or 3 ton unit.

or was every unit on the street installed incorrectly?

http://farm6.static.flickr.com/5185/5664177315_57b5b0af23_o.png

Funny I thought we were talking about your basement not your whole house? Looks like a one ton AC will do you nicely in the summer and a 1 1/2 ton HP if you need heat for the winter and don't want to use much of your heat strip or just go with a one ton HP. Most AC's just for basements are way to large because most techs don't do load calculations and are afraid to go low. I know better. Thank you very much

dan sw fl
04-29-2011, 07:00 AM
Funny I thought we were talking about your basement not your whole house? Looks like a one ton AC will do you nicely in the summer and a 1 1/2 ton HP if you need heat for the winter and don't want to use much of your heat strip or just go with a one ton HP. Most AC's just for basements are way to large because most techs don't do load calculations and are afraid to go low. I know better. Thank you very much

1.5 TON HP will not provide close to the Calculated 35,000 BTU/hr for Central NJ ranch. I believe Heat IS generally NEEDED in central NJ in the Winter.

alecmcmahon
04-29-2011, 07:39 AM
1.5 TON HP will not provide close to the Calculated 35,000 BTU/hr for Central NJ ranch. I believe Heat IS generally NEEDED in central NJ in the Winter.

Agreed, it gets pretty damn cold here in the winter. But i wont be going with a heat pump, im sticking with my hot water baseboard heaters.

Thanks everybody for the tips.

glennac
04-29-2011, 08:29 AM
1.5 TON HP will not provide close to the Calculated 35,000 BTU/hr for Central NJ ranch. I believe Heat IS generally NEEDED in central NJ in the Winter.

Well gees I was refering to the basement only. I guess I should have spell it out even more. A 1 1/2 ton HP was for the basement only. Now since heat is not needed a one ton is all that is needed for the basement and not the rest of the house. Thank you, thank you very much

alecmcmahon
04-30-2011, 05:56 AM
Well gees I was refering to the basement only. I guess I should have spell it out even more. A 1 1/2 ton HP was for the basement only. Now since heat is not needed a one ton is all that is needed for the basement and not the rest of the house. Thank you, thank you very much

Yeh, Im just a little confused why my load calc says there will be ZERO heat gain in my basement, yeh... it's mostly below grade, but it does get warm down there in the summer time.

Basement @ 875 sq feet, with a 36,000 BTU Oil Fired boiler down there, and will have plenty of electronics and stuff when finished, i figure it'd require at least 1 ton of cooling?

So glennac, if your reccomending 1 ton of cooling for JUST the basement, ...+ the 2 tons for my main 900 sq ft living space = 3 Tons. ????

Robert O'Brien
04-30-2011, 06:53 AM
Yeh, Im just a little confused why my load calc says there will be ZERO heat gain in my basement, yeh... it's mostly below grade, but it does get warm down there in the summer time.

Basement @ 875 sq feet, with a 36,000 BTU Oil Fired boiler down there, and will have plenty of electronics and stuff when finished, i figure it'd require at least 1 ton of cooling?

So glennac, if your reccomending 1 ton of cooling for JUST the basement, ...+ the 2 tons for my main 900 sq ft living space = 3 Tons. ????

36K oil fired boiler? I've never heard of anything under 60K

udarrell
04-30-2011, 07:44 AM
Yeh, Im just a little confused why my load calc says there will be ZERO heat gain in my basement, yeh... it's mostly below grade, but it does get warm down there in the summer time.

Basement @ 875 sq feet, with a 36,000 BTU Oil Fired boiler down there, and will have plenty of electronics and stuff when finished, i figure it'd require at least 1 ton of cooling?

So glennac, if your recommending 1 ton of cooling for JUST the basement, ...+ the 2 tons for my main 900 sq ft living space = 3 Tons. ????
NJ, summer design is almost identical to Madison, WI.
Doubt the basement would need more than a half-ton.

Winter design at 99% is 10F, Trenton is 11F; warmer than Madison, WI at minus -11F; La Crosse, WI -13F.

A 'well done' manual J ought to get the HT-gain HT-loss close enough.

alecmcmahon
04-30-2011, 07:44 AM
36K oil fired boiler? I've never heard of anything under 60K

My mistake… it's 117k oil fired.

Which also does my hot water domestic in the summer time.

glennac
05-01-2011, 09:50 PM
Yeh, Im just a little confused why my load calc says there will be ZERO heat gain in my basement, yeh... it's mostly below grade, but it does get warm down there in the summer time.

Basement @ 875 sq feet, with a 36,000 BTU Oil Fired boiler down there, and will have plenty of electronics and stuff when finished, i figure it'd require at least 1 ton of cooling?

So glennac, if your reccomending 1 ton of cooling for JUST the basement, ...+ the 2 tons for my main 900 sq ft living space = 3 Tons. ????

You got that right. One ton for the basement and 2 upstairs. Of course you could just put your AH/furnance in the basement and feed the AC up stairs and let the air flow through floor vents back to the basement with free air flow (no duct) and your basement will be fine the whole summer with good ventilation and no humidity problems. Your call. Thank you very much

alecmcmahon
05-01-2011, 10:00 PM
You got that right. One ton for the basement and 2 upstairs. Of course you could just put your AH/furnance in the basement and feed the AC up stairs and let the air flow through floor vents back to the basement with free air flow (no duct) and your basement will be fine the whole summer with good ventilation and no humidity problems. Your call. Thank you very much

3 ton was initially my gut feeling, from talking with neighbors of the same house setup, they have a 2.5 systems , and do NOT send air to the basement. So i figure 3 tons.

But, .. According the hvac calc that i put every little detail in keeps recommending 2.5 TON, which of half ton ( 6511 btu ) are needed for the basement.

Basement will act as a second family area, Will have TV's , bathroom, laundry area, computers, etc. and prob. 2-4 people when occupied. and the bottom 6 feet of the total 8 feet height is below grade.

I just cant picture being able to cool the entire basement with what is the equivalent of one of my old small 6000 btu window units.

This has been the hardest decision of my life! 2.5 or 3! 2.5 or 3! ahhh.

Here is what my manual J came out to be,... I guess numbers dont lie ? just concerned about basement.

http://farm6.static.flickr.com/5303/5678401380_093c1e56a7_z.jpg

udarrell
05-01-2011, 11:39 PM
3 ton was initially my gut feeling, from talking with neighbors of the same house setup, they have a 2.5 systems , and do NOT send air to the basement. So i figure 3 tons.

But, .. According the hvac calc that i put every little detail in keeps recommending 2.5 TON, which of half ton ( 6511 btu ) are needed for the basement.

Basement will act as a second family area, Will have TV's , bathroom, laundry area, computers, etc. and prob. 2-4 people when occupied. and the bottom 6 feet of the total 8 feet height is below grade.

I just cant picture being able to cool the entire basement with what is the equivalent of one of my old small 6000 Btu/hr window units.

This has been the hardest decision of my life! 2.5 or 3! 2.5 or 3! ahhh.

Here is what my manual J came out to be,... I guess numbers don't lie? just concerned about basement.

http://farm6.static.flickr.com/5303/5678401380_093c1e56a7_z.jpg
Well, I cool the entire first floor of my farm home with a 6,000-BTUH window unit & a WindMachine 3300 floor type fan to circulate the air through all the rooms.

It depends on how much runtime your central unit will have on the main floor areas.

You will have to have the proper amounts of air delivered to the basement & to the other rooms so they all cool equally based on the main control thermostat.

An accurate manual J will help the Tech do that. Make sure all branch duct runs have adjustable dampers so air flows can be fine tuned.

The basement will need good airflow circulation; so discuss with the contractor/Tech how you're going to achieve it!

If it's done right I believe it can be balanced out to properly cool all areas including the basement with its added loads.

Make sure duct sizing & everything is done right...

I personally would never oversize the condenser tonnage.

You do want the evaporator coil sized to handle the CFM required for heating or it will have too much pressure-drop, driving static-pressure up; reducing blower efficiency & usually reducing airflow.

That usually doesn't happen unless heating is oversized in very cold climates & cooling is 1.5 or 2-ton. Always Check to be sure...

alecmcmahon
05-02-2011, 12:28 AM
Well, I cool the entire first floor of my farm home with a 6,000-BTUH window unit & a WindMachine 3300 floor type fan to circulate the air through all the rooms.

It depends on how much runtime your central unit will have on the main floor areas.

You will have to have the proper amounts of air delivered to the basement & to the other rooms so they all cool equally based on the main control thermostat.

An accurate manual J will help the Tech do that. Make sure all branch duct runs have adjustable dampers so air flows can be fine tuned.

The basement will need good airflow circulation; so discuss with the contractor/Tech how you're going to achieve it!

If it's done right I believe it can be balanced out to properly cool all areas including the basement with its added loads.

Make sure duct sizing & everything is done right...

I personally would never oversize the condenser tonnage.

You do want the evaporator coil sized to handle the CFM required for heating or it will have too much pressure-drop, driving static-pressure up; reducing blower efficiency & usually reducing airflow.

That usually doesn't happen unless heating is oversized in very cold climates & cooling is 1.5 or 2-ton. Always Check to be sure...

Will a 20x20x30 return trunk with 16" flex on a 18x25 grill and 12"x18"x10' supply trunk with 8" flex ducts to each 8 rooms suffice ? Also 2 8" supply's to basement and 2 8" returns work well for 2.5 ton system ?

udarrell
05-02-2011, 09:32 AM
Will a 20x20x30 return trunk with 16" flex on a 18x25 grill and 12"x18"x10' supply trunk with 8" flex ducts to each 8 rooms suffice ? Also 2 8" supply's to basement and 2 8" returns work well for 2.5 ton system ?
Read all you can find on the subject.

For liability reasons, I cannot stick my neck out by telling you & your contractor(s) how to design the duct system & airflow to & from the rooms & basement living area.

One has to be there to begin to design a duct & airflow system.
Manual D has a lot of good guidelines to utilize.
Good Luck.

glennac
05-02-2011, 06:17 PM
3 ton was initially my gut feeling, from talking with neighbors of the same house setup, they have a 2.5 systems , and do NOT send air to the basement. So i figure 3 tons.

But, .. According the hvac calc that i put every little detail in keeps recommending 2.5 TON, which of half ton ( 6511 btu ) are needed for the basement.

Basement will act as a second family area, Will have TV's , bathroom, laundry area, computers, etc. and prob. 2-4 people when occupied. and the bottom 6 feet of the total 8 feet height is below grade.

I just cant picture being able to cool the entire basement with what is the equivalent of one of my old small 6000 btu window units.

This has been the hardest decision of my life! 2.5 or 3! 2.5 or 3! ahhh.

Here is what my manual J came out to be,... I guess numbers dont lie ? just concerned about basement.

http://farm6.static.flickr.com/5303/5678401380_093c1e56a7_z.jpg

Sounds good to me. I would go with 2 1/2 tons and put a couple of 6" ducts for the basement with manual duct dampers to control or shut off the flow and let the air free flow through the basement to your unit through floor vents.

Probably won't even need little if any a/c supply air to the basement with that set up. That is how I would go. Thank you very much.