Messed up systems Need opinions

Old 12-01-15, 05:35 PM
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Messed up systems Need opinions

Ok i have problems... my house is 1500 sq ft
i have 2 furnace 55,000btu 3ton and a 65,000btu 3.5ton

I drew out some plans very off scale but hopefully you get the idea

Brown are supplys from basement furnace
red are supplys from attic furnace
orange box between bath and living room is attic furnace
blue is the ducts from basement to 2nd floor
green is basement return
green black is attic return

pretty sure all supplys are 6"

the basement furnace does not put enough air out to 2nd floor bed rooms
attic furnace puts too much air out all vents to where its hitting you in the face very un even
most importantly gas bill is 350-400$ a month during winter i think it should be half that
electric bill is about the same during summer

now my step brother had a solution which i liked. he has a hvac company

remove basement furnace put 90s on the supply line that goes from basement to 2nd floor and put 3 zone dampers in for the 2nd floor bedroom and 1st floor bedrooms and the rest of the house. tap into the 2nd floor return and add a low return inbetween the bath and living room from the attic down a bay in the wall. i like this because im more than likely going to want my bedroom(2nd floor) a different temp than the rest

i had a buddy of mine come in and tell me hes out of his mind thats way too much work keep both furnaces if anything have the attic feed the 2nd floor and have just the basement feed the 2 1st floor bedrooms. to me that sounds like over kill for one unit

what im looking for is the most efficient way. i already have zone dampers transformer board duct work collars.

still with me? would love to hear some more opinionsName:  Untitled.jpg
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Old 12-02-15, 03:57 AM
Join Date: Oct 2008
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Hi Brett,
I'm not a hvac pro, but will follow to see what they have to say. Overlapping two forced air systems, whether that is due to mixing supplies in the same room or just the same floor is complicated. With one on and the other off, supplies can become returns.

What I didn't hear is the starting point. You should first evaluate your heating and cooling requirements (manual J), then have a duct design done to meet those requirements, along with how close those two systems fit the design.

Reducing energy costs starts with reducing energy loss. Two systems looks to me like throwing money at a poorly insulated home.

I'll be watching
Old 12-02-15, 09:38 AM
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Agree with Bud on his scenario - plan correctly first, then fix. Insulation could be included in that plan.

Not an HVAC expert, but I have a two-story house and switched from one unit / one thermostat to one unit / dual zone thermostat with automatic dampers and noticed energy savings. I also like providing better comfort to the areas I want. Sounds similar to what your brother recommends.

Good luck
Old 12-02-15, 09:51 AM
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It's insulated fairly well. There is sprayfoam on the crawl space walls. Insulation in all the bay's in the crawl in all the outside wall and in the attics. The crawl even has 1" foam blocks nailed under the insulation.
Old 12-02-15, 10:46 AM
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the basement furnace does not put enough air out to 2nd floor bed rooms
attic furnace puts too much air out all vents to where its hitting you in the face very un even
The overlap is clearly the issue. Why is the basement system supplying anything to the 2nd floor? That should all be handled by the attic unit.

Basement unit should handle the basement (if climate controlled) and the 1st floor.
Attic unit should handle the 2nd floor.

As mentioned previously, a manual J needs to be done and then each unit evaluated to see if it's over or under rated for the space it's conditioning.
Old 12-02-15, 12:22 PM
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I'm not at all clear on what the problem is that you're trying to solve.

Are these two (2) furnaces currently installed and failing . . . . or in need of improvement before winter actually sets in ?
Old 12-02-15, 02:22 PM
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im going to say the reason the overlap is because at one point it was just the basement unit. they added the attic one because the living room and kitchen were barely getting any air flow im guessing because the long runs. another reason why they used the attic one is they just cut holes in the ceilings instead of chasing it to the crawl space and through the floor

i do agree the attic should do the 2nd floor and the basement should do the first but the total square footage for the entire upstairs is under 500 sqft so to me its way too much for just 2 rooms. and like i said i hardly get any kind of air flow in the kitchen from the basement unit.

i dont think either system is failing i just think each system i just think the duct routes are wrong and inefficient

manual J sounds like the right route but i dont have that knowledge nor know anyone who does or has that software. i measured them up like 95% hvac contractors do by sq ft. per room

the thing i really hate is when the attic unit is running (depending on season) winter hot air blows directly into your face and doesnt spread evenly across the room, and of course summer cold air blows into your face and doesnt spread evenly across the room. very uncomfortable.

confused on what to do lol

Last edited by brett14; 12-02-15 at 02:49 PM.
Old 12-04-15, 05:55 AM
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The supply registers can be changed to help with the air mixing better. Thats an easy fix. But yes you MUST get a manual J done before anything else. Sizing by square feet is no longer viable in the modern age. Those guys are one lawsuit away from going out of business. Not many mom and pop company's can afford to replace a system in a finished home.
Old 12-09-15, 07:11 AM
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If your step brother has an HVAC company then get him to do the manual J, S, and D calculations. If he has no clue you don't want to be his trial and error test case.

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