AC and furnace help

[jbmrider]

I'm looking for some advice, please. We need to replace our furnace and A/C. We live in NJ and our house is a 1957 split level with about 2500 sf, not including the basement (where furnace is located) which is an additional 500. We also need to move the location of the A/C unit from the back to the side of the house (which didn't seem to be a concern).

We received 2 quotes so far:

The first was for a Rudd 90% 100K BTU, 4 ton, 13 seer. Price $x. A second price was given for an 80% 125K BTU, same A/C, for $x. I was told the Rudd systems are all variable systems.

The second was for a Goodman 80% variable 115K BTU, 3.5 ton, 14 seer (said runs as a 15 Seer?). He ran a duct calculation and said our ducts wouldn't support a 4 ton but he would update the coil to a 4. Price $x.

Are we better off with a 90% furnace and 13 Seer or 80% with a 14-15 Seer? Any thoughts on the size of the A/C? Is there any appreciable difference between Rudd and Goodman?

Any advice would be greatly appreciated!

[mechanical'al]

do your homework this site is a great start go on the locater insist on load calc to be done and find a good installation contractor, who makes the equipment really dosent matter its all in the installation and service after the sale as even the best piece of equipment ( if it did matter ) is only as good as its properly sized install

[udarrell]

I'm looking for some advice, please. We need to replace our furnace and A/C. We live in NJ and our house is a 1957 split level with about 2500 sf, not including the basement (where furnace is located) which is an additional 500. We also need to move the location of the A/C unit from the back to the side of the house (which didn't seem to be a concern).

We received 2 quotes so far:

The first was for a Rudd 90% 100K BTU, 4 ton, 13 seer. A second price was given for an 80% 125K BTU, same A/C. I was told the Rudd systems are all variable systems.

The second was for a Goodman 80% variable 115K BTU, 3.5 ton, 14 seer (said runs as a 15 Seer?). He ran a duct calculation and said our ducts wouldn't support a 4 ton but he would update the coil to a 4-Ton.

Are we better off with a 90% furnace and 13 Seer or 80% with a 14-15 Seer? Any thoughts on the size of the A/C? Is there any appreciable difference between Rudd and Goodman? Any advice would be greatly appreciated!

NO Prices; forum rules!

It appears they are way oversizing both heating & cooling equipment.

Newark NJ is the highest cooling design at 91F & 73F wet bulb for 43%; the other major cites of Trenton 88F/74; Atlantic City; 89F/74F.
Normally, not a lot of work, you ought to be able to get it to 12-Btuh per sf, or 30,000-Btuh, or a 3-Ton, some at 34,000-Btuh.

The 90% would usually require 1364-CFM of airflow; 3-Ton cooling 1200 to 1300-CFM of airflow.
That may be all the duct system can handle efficiently; if that.

A manual D performed on the duct system would be a good idea; seal every bit of it with mastic.
A heat & A/C load-calc should be performed before making any decisions.

This is a simple Whole House load-calc to get a ball-park look at equipment sizing; I'd use R-5 for walls, until you know the R-values; look in the attic, use R-2 for windows with storms; I'd use a rather high .7 or .8 for infiltration.

Read all the simple instructions; have the contractor run a load calc., you need to know that information; print the calc when completed, - as you can't save it!
http://www.loadcalc.net/

[beenthere]

You need someone to do a load calc and find out what size furnace and A/C you need.

[jbmrider]

Could I be confusing "duct calculator" with "load calculator"? Is there both or was it likely that a load calculation was done and I'm confusing it?

He did in fact say that his calculation (whichever one!) supported a 3 ton, but then still priced a 3.5 ton. Perhaps from the size of our home??

Any advise or suggestions about whether we should go with a higher efficiency 90% furnace and 13 SEER or 80% variable with 14 SEER (or any other combination)? I'm assuming these are separate issues from the load calculations?

Thank you for all of your help!

[beenthere]

If it came out to 3 tons, best to go with 3 ton. What size furnace did it come out to.

[jbmrider]

I was told 105K BTU. Sounds like he may not have run calculation on furnace (just A/C) and looked at house square footage. Does that sound right?

[udarrell]

I was told 105K BTU. Sounds like he may not have run calculation on furnace (just A/C) and looked at house square footage. Does that sound right?

Many load calc programs do both heating & cooling loads at the same time. 105K heating looks way too big...

The one I'm using now, automatically selected the winter design at 70F indoors & 14F at 97.5% for a 56F temp-difference; using 99% it is 10F design temp & a 60F temp-difference; I tend to use the 99% or in this case 60F temp-difference. 57,000-Btuh / 2500-sf is about 22.8-Btuh per sf.

It only showed around 40K-Btuh, which may be low; a 60K-Btuh at 57K-output or, an 80K @76K output should cover the heating load with plenty of reserve.
On the homes with temp differential of 62F the Btuh/sf area was 21-btuh per sf area * 2500 is 52,500-Btuh Of course that can vary, depending on what you do to make it WORK....

However, do not pay any attention to what I guesstimate, as I don't know the proper input numbers, rather find someone to do a proper ACCA approved heat & cool load-calc.

By all means, get a load-calc for heating.

[motoguy128]

I was told 105K BTU. Sounds like he may not have run calculation on furnace (just A/C) and looked at house square footage. Does that sound right?

That's very common, but not the correct way to do sizing. I could show you a 3200sqft home that needs 3 tons of cooling and a 60k furnace and another that needs 100k and 5 tons, both in the same climate. A spray foam insulated and ICF foundation and underslab insulation, 2500sqft home the same style and size as your might need as little a 2 tons of cooling and use a heat pump with a hot water coil using the domestic water heater could supply the 10-15k BTU of heating it would need on the coldest days and for defrost.

It cna vary dramatically. OVersized equipment makes a home less comfortable and uses more energy. Especailly AC.


My 3200sqft 86 y/o home only need 4 tons of cooling and about 65k BTU heating in a climate that more extreme, both hotter, more humid and colder than NJ. But every home is different and unique.

[jbmrider]

Thank you all for the feedback. Once I get the sizes right, any thoughts about the efficiency?

[mechanical'al]

get prices on both efficiencies and compare knowing your utility rates to offset price diff. and pay back time

[jbmrider]

How do I calculate in order to compare? Is there a specific formula to use?
Thx!

[jbmrider]

Hi All-

How important or not is it to have a chimney liner for an 80% high efficiency furnace? Also, should we have a humidifier installed (NJ climate) if we have forced hot air? Is a separate filter a good idea?

Here's where I am with the A/C and Furnace:

First contractor A(with whom has been servicing us for 5 years and is a family member of a close friend), suggested a 3.5 ton, 80% 2 stage 110,000 BTU.

Second contractor B, ran a manual J-Load, said we need 3 ton, 80% 2 stage 80,000 BTU. Suggests a chimney liner, separate filter, and gave an option for humidifier.

When I discussed with contractor A, the findings of the j-load from contractor B, he said his calculations came up with a 3 ton too but he still is opting for 3.5 ton because our house is a very long split and tends to have hot "pockets". He said he wouldn't be comfortable installing the 3 ton. For heat, he did a "standard" calculation for roughly 50 BTU's per square foot. He said he could set the speed so the BTU's shouldn't factor in that much. He doesn't put in liners and doesn't think it is necessary unless the chimney is eroding.

Any thoughts here? I have a relationship with contractor A but contractor B was very thorough. Are the differences here very significant or marginally so? Thanks!

[udarrell]

Well, my very rough heat-loss calc got around 56,000 design heat-loss; I don't say that is accurate due to the differential of inputs.
However, I believe their heat loss is too high... but I'm not there...

[mechanical'al]

well w/ a few exceptions a chimney liner is national code
as for the a/c upsizing is not a good idea
what a standard calc. is ??? a guess !!! one should never guess
read through some posts on this site

[jbmrider]

Thank you for your feedback, udarrell and mechanical'al!

Is upsizing on the furnace equally as "bad" as the a/c? What are your thoughts on the humidifier and separate filter? I'm trying to keep costs down (aren't we all) but also want to make sure this is done correctly from the start.

Thanks again.

[mechanical'al]

depending or your pesonal prefrences , how tight of a structure , previous comfort levels?
how is the humidity level now in full winter if its really dry then youll need one if not save some$
as far as air cleaner thats also personal ? allergies? sinus issues ? I M O cheap . 50 cent filters a best buy by the case and change them monthly no worries