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wrldruler 09-11-2008 04:09 PM

Ductless versus Central Air Upgrade ???
We're converting our 300 sq ft garage into a family room. Trying to decide between a running $2,000 worth of duct versus buying a $4,000 ductless mini-split system. My preference is to go duct and tap into my central air.

But I am worried that it will be too warm in the summer. I've got a dual-zone system. 1.5 ton for the 600 sq ft upstairs and 1.5 ton for the 600 sq ft downstairs. Calculations show we have almost exactly 300 sq ft capacity left downstairs. It will be close.

Another thought: My Armstrong central air system is 13 years old. It may be getting close to the end of its life. I am thinking about going duct, and if it is too warm, upgrading the end-of-life Armstrong to a higher tonnage.

My question: How much does an average system replacement cost? I want to replace both the condensor and evaporator coil.

Can you give me parts and labor seperate? I've got family in HVAC that can do labor free if I provide enough beer.



dac122 09-12-2008 08:18 AM

If you've got family in HVAC, then why will it cost $2000 for just duct work?

You are correct, you should replace both the the condenser, outdoor unit and maybe fan.

Again, if you have family in HVAC have them come over and do a Manual J and Manual D. That will give you your answer as to whether your current system and duct work will suffice. The cost of beer to have them help is too high if they don't know what or how to run a Manual J and D.

BTW, I'm still running an 18 year old York, so at age 13 your system could still have plenty of life left in it, unless you find it will be undersized for your remodel.

wrldruler 09-12-2008 09:58 AM

To answer the question about "why don't I just call my family"?

(1) I am pulling a permit to do the renovation. Family may not be able to pull a HVAC permit.

(2) I am willing to spend a thousand or two, NOT to have to deal with family. I would rather do business with a stranger. Then I can rip them a new one or hire a lawyer if something goes dreadfully wrong.

(3 My Dad is an old-school duct man, and doesn't do system install & service. He doesn't know anything about ductless minisplits, and hence he doesn't agree with me getting one. My cousin is an install & service man, but doesn't do duct. My cousin is an a-hole. Both live 2+ hours away.

I am just weighing all my options. Going with family may be difficult.



dac122 09-12-2008 10:45 AM

I completely understand the family and friends can't-complain-when-its-free dilemma.

Then I would get some quotes, and make sure they do a Manual J and Manual D for that part of the house. If you don't have specifics for your remodel on insulation values, number, size and type of windows and doors, then the calcs cannot be done until you do. Ask to see their numbers from the Manual J in particular. Once you have the numbers it will then be clear whether that 1.5 tons will work for the added area.

wrldruler 09-12-2008 06:56 PM

Did a HVAC-CALC tonight.

Existing: 10,000 Gain, 29,000 Loss
Garage: 6,500 Gain, 13,500 Loss
Total: 16,500 Gain, 42,500 Loss

I have a 1.5 ton 10 SEER A/C, and a 40,000 BTU furnace.

So I am close. But is it too close? Any advice?



dac122 09-12-2008 07:14 PM

What is the stated cooling capacity of your 1.5 ton unit? They are not always the same.

I'm now seeing the problem. It may be very close to call.

Being slightly under on your furnace should not be a problem.

Kizzl775 09-13-2008 10:00 AM

i dont see any reason why your system now cant hold up for the time being. i mean as far as doing what it is supposed to do. well you got 2 zones at 1.5 ton on 600 sq ft both with 40,000 btu furnaces right? ok well 1.5 ton will cool well over 600 sq ft and as for the furnaces, lets just say on the high side you need 50 btu per sq ft 50 * 600 = 30,000 btu so honestly you would be right in the ball park on that side but nothing to offbalanced to worry about.

dac122 09-14-2008 09:12 AM

Some more thoughts and questions.

1. What is your furnace? Depending here a minisplit might be more economical, or more expensive to heat.
2. Based on your current duct work what does HVAC Calc say you will need? Is it even feasible to run the size of duct and branches HVAC Calc says you'll need for this remodel? Will you have to change your entire duct system?
3. Did you plug in all proposed insulation values, windows, doors, etc. into HVAC Calc, or just the way it is now?

1. HVAC Calc is supposed to follow a Manual J. Manual J is allegedly conservative, meaning that number is more of a worst case.
2. Is it too late to make changes to your remodel to lower heat gain? You can always add in a window or skylight later if the system is working good.
3. Get your ID coil model number, and maybe, just maybe, it can mate with a 2 ton unit and still achieve the stated SEER. This is a long shot and at best you probably won't mate with anything greater than a 13/14 SEER. Check the ARI Directory.
4. Cross post to hvac-talk's residential section. There are actual pros there that do this all day long.
5. Kizzl775, please be careful in using the square footage method. The OP has effectively used Manual J, which is far more accurate. It is easy to come up with identical square footage designs but drastically different heat gain/loss.

TazinCR 09-14-2008 10:59 AM

Here in Costa Rica 95% of all A/C is mini split and they seem to work great. Here I just bought a 18000 BTU installed for $850. Shop around on price.

pearnakata 09-25-2008 01:05 PM

I would go with the mini split. I decided to spend the extra money and can tell you its well worth it. Plus it kept me warm when my main furnace wwent down last winter. Cheap to operate too.

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