Changing An Existing Residential HVAC System...

gonefishin

Hi all,

I am the current homeowner of a two story (2900 sqft) home that has some heating and A/C problems. We moved into the house about seven years ago (the house was ten years old when we bought it). The heat and air have never worked very good. In winter the upstairs is cold. While in summer the air just cannot keep up if the outside temp gets above the low to mid 90's. The inside air will get over 80 degrees when it's 95+ outside, but the humidity will be low (at least that makes it bearable).

I've been told that my ductwork, A/C and furnace are all undersized. The heat is supplied by a single stage 100,000BTU gas furnace. The A/C unit is 3 ton. I have had three companies give me estimates and all thought that the ductwork was also undersized. I'm going to be living in this house for a long time to come, so I don't want to make the same mistakes that the previous owners made. I understand that there are limitations that I can have done to the duct work (to to this being an existing house). But I would like to come up with a compromise that does work.



Two of the guys that came out to look at the house had suggested that the ductwork that they have access to (both vent and return) all be redone. Because they would still be limited on the size of the vents and returns (because of gas lines etc), they would only recommend a a4 ton AC unit (max) (even though they stated a 5 ton would better suit the house).

One guys had stated that expanding the size slightly where the current ductwork is would still limit the size of the AC and furnace units. But he suggested expanding the return lines that are accessable...and splitting the vent side into two sections. Using the existing section as is for the first floor vent (9vents) and adding a paralleled vent section that would carry all the second floor vents (9 vents). He had said that you can then go with a 5 ton AC unit. He also said that running the 1st floor and second floor like this we will also have a little more control to dampen down the first floor heat in winter so the upstairs isn't quite as cold. I haven't got the estimate back from him yet. This all sounds like it would work to me...but what do I know??? Does this sound like a feasible solution that will work in my situation?

I understand that it's impossible to assess a situation without seeing it for yourself. But I appreciate any and all advice. If you need any other info or clarification please ask.

Thanks!
dan

watersda

Can you add a second unit in the attic? The existing unit can be used for the 1st floor and the new one for the second floor. Remove/block off existing ducts to 2nd floor. Add new duct work in the attic for 2nd floor.

gonefishin

That is an interesting idea. I'm not sure why...but attic units aren't used that much around here (Chicago area). The few people I have heard of ,with an attic unit, had it put in during initial construction. I'm not sure how it would be to add the 220V line to the second floor attic. I'll ask around though and see what I can find out.

thanks,
dan

MechanicalDVR

Well ther eis no reason to add a 220v line to the attic, if you were going to add heat and air it would only be a 120v line for the furnace.

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watersda

I have recently learned that high efficiency (90% or more) furnaces shouldn't be put in cold climate attic spaces. By design, the high efficiency furnaces produce condensation, which needs to be drained off. In colder climates, an attic units drain lines can freeze causing problems.

mdshunk

So far, we aren't talking about a furnace in an attic.

Yes, you're right. Most every good fossil fuel furnace nowadays willl be of the condensing type. That is a design consideration, which is easily overcomeable by other means. For instance, a heat pump will non condense in heating mode. Every walk-in freezer that has been installed in the last 50 years has had a heat tape in the condensate line, which is another way to address the condensate from an attic gas furnace.

Never say never.

gonefishin

Huh...I wouldn't have guessed that the air portion would have been 120V. Thanks for the clarification.





We'll definitly in a cold weather climate. Perhaps this is why they're not very popular around here?



Any thoughts or help on the original question?

thanks,

dan

MechanicalDVR

Two systems are always better than one. Adding a new system to the attic and removing the second floor runs from the existing system is a good way to go. If you are going to be in the house for any length of time you will appreciate the comfort of two systems.

__________________
"Injustice anywhere is a threat to justice everywhere" mlk
100% Union and Proud of It