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02-07-2013, 06:42 PM #14Professional Member*
- Join Date
- Dec 2010
- The Quad-Cities area (midwest).
02-07-2013, 07:24 PM #15
Also, do everything possible to lower the heat-gain into your home, also make sure the duct system is properly sized, sealed, & insulated if not in a conditioned area; with a 1.5-Ton setup doing all that, - should save money on your utility bills.
The 2.5% summer design in Austin TX is 98-F dry bulb, 77-F wet bulb, it is very dry there.
A properly setup 1.5-Ton system with home energy efficiency work performed, should handle 1000-sf home. However, that is for you & the contractor there - to figure out.
02-07-2013, 07:29 PM #16Professional Member*
- Join Date
- Jul 2010
Sizing is going to be more about comfort and less about energy savings. Does the 3 ton keep the humidity under 50%? If so leave it in until it dies.
02-07-2013, 08:08 PM #17
Why not get something to measure the humidity in your house & see how high it gets. If it doesn't get any more than 55% RH then I wouldn't change anything. If you're comfortable in the house & the humidity is O.K. where you don't have to worry about mold that's all that counts. It might cost a little more to run do to more stopping & starting but negligible compared to the cost of new equipment.
Even if short cycling is hard on the equipment you still have nothing to lose by running it as long as it holds out.Gary
An engineer designs what he would never work on.
A technician works on what he would never design.
02-07-2013, 08:47 PM #18Professional Member*
- Join Date
- May 2008
Agree with Marty, just run it till it dies. Why not?
02-07-2013, 09:04 PM #19
Well, my last post agreeing, was lost so I'll do a short form.
I agree with the last three posts, because Austin TX is a fairly dry area & if the blower is slowed to 350-CFM per-ton or 1050-CFM; I believe the humidity with a reduction in infiltration would be okay.
02-08-2013, 12:52 AM #20
The answer to this questions can only be answered by you as you are the customer and live in your home not us. The electic bill while not horrible can be better but I think you might be having other problems? In other words something has promoted you to consider changing out the system. A proper load cal needs to be preformed to determine what size system is needed to keep your home comfortable. While a (1.5) might be a good idea without a load we are guessing as is your installing company.
Example of home oversized that we finished up a install on today. House had a (3) ton in it and has 1250 square foot with average windows and insulation that had been replaced within the last few years. While the customers current system maintained temp and somewhat keep them comfortable. While sizing the home out a week ago the customer said that while the system works good it just doesn't feel like it 75 inside all though the t-stat says so. Come to find out the humdity level in the home was very high. After proper load was done the home only required (2.3) tons of cooling. So I sized per manual s a (2.5) ton that meet the full capacity and matched sensible load within 100 btu's of what was needed. Know the system is sized propely and will handle the full load of the home and on 95 plus degree days will run longer by design remove humdity. We installed a variable speed furnace with single stage outdoor unit to achive this. So to recap now the customer has a 16 seer unit that will control humdity and heat and cool the home properly. They will pay less $ to stay comfortable. The upfront cost is one thing but again comfort has value.
It's not just a plug and play. What good contractors do is as listed above. I can't stress enough to make sure whoever sizes your new system preform a load cal to ensure the amount $ you spent is well spent and will provide comfort while costing you less $ to do so.
02-08-2013, 08:49 AM #21
1937 is a real mix. It will depend on your area. Hwoever, if its' brick or stucco exterior, it's probably nearly as tight as average modern construction. Without a blower door test, you won't know. You utlity bills will give some clue.
Finally, older homes often have denser materials. Plaster, brick, hardwood, tile, stucco, all have more mass than many modern mass produced counterparts. That mass will allow you to have a smaller AC system.
With only moderate insulation, even in Austin, if you have descent shade or deep roof overhangs/eaves, 1.5 tons could be plenty. WHere i live is nearly as hot and humid in mid simmer and a 1500sqft upstairs of older homes can be cooled with 2 tons.
Thermal Mass + Shade = smaller AC system even with only moderate insulation.
02-08-2013, 11:42 AM #22
02-08-2013, 11:53 AM #23
Moving into my current home comming from a late 60's home was pretty eye opening. I'm probably spoiled in that my home was built by somone with deep pockets, but I think some industry paractices and meterial selection was pretty good overall.
We focus so, so hard on raw insulation values, when the overall envelope, integrated shading, building orientation and wall material seletcion, from what limited expereince I have, makes a much bigger difference. I think this is what hte guys on the Building Science side of thsi forum are trying so hard ot get people to understand. That an taking the opposite approach to home energy. Rather than size equipment to a heat loss/gain value, you build a home to a target heat loss rate instead. It doesn't have ot be a net zero home either. I think that last step is diminishing returns and forces comprimises, like less window area.
Farm home however, tend to be DIY and sometimes are more limited in materials available due to logistics. Sometiems they are very well constructed, other times not. They also frequently have additons added. IN 1937 it might not have even had electricity. So it would have good ventilation and possibly shading with nearby shade trees to keep cool and a nice big porch (you don't want to be indoors in late afternoon). Some even had a outbuilding called a "summer kitchen" because its too hot in mid summer to cook indoors. You would set up a table and eat outdoors as well... probably in the shade... then retire indoors at near sunset to a reasonably cool home. Attic werent normally vented... but roof material were more heat tolerant (asbestos shingles, metal shingles or standing seam, wood shakes. Actuually with tile or wood shakes, you want that attic heat to dry them out after a rainstorm.
02-08-2013, 03:15 PM #24