95% of gas furnace systems, sure. Air handlers for heat pumps where duel fuel is not implemented are virtually always coil first. But then you must know that, so I'm a bit perplexed by your replies.
Originally Posted by Airmechanical
I'm feeling ya. I got whacked by a hack. He didn't do a calc. Says, "3 ton.. A little large but should be OK." wtf. I didn't know calc's existed until I came across this site.
Originally Posted by airtime
I have R13 in walls R30 in ceiling. Crawl space with no insulation. Dual pane winders. 3/12 pitch on the rafters. Wood siding.
The more I learn the deal, the more pissed I get at the installing contractor.
Bordering legal action if this keeps up.
My calc's came out to 2 ton and 56k heat
I can't yet enjoy this HP to tell if I even like them or not.
I can't fully enjoy this system to even find out if I like HP's or not. Third season like this. Stop the pain. Oh the humanity.
Here's my understanding - it depends on your backup heat mode. If your backup heat is gas, then the coil can go anywhere - either the furnace is running, or the heat pump is running. Not both.
Originally Posted by regis101
If your backup source is electric, then the coil HAS to be on the return side. Otherwise, the HP can't add heat to the air (it needs to add it's heat first).
Thanks for the clarification, Waterloo.
Always better to put the coil in the return
- Heat stages will work together. They can't if coil is in the supply because head pressure rise.
- Coil isn't exposed to Aux heat
- No need to cycle aux heat during defrost cycle
Very very very common with electric stips as Aux.
oil or gaz furnace :
Always put the coil in the supply
- Condensate on oil pot, corrosion, Leak if in the return.
- Must use a plenum sensor to cycle the aux heat during defrost
I'm having an "A-ha" moment. Thank you
That 14" return to the 3ton HP is waaaaaay short of required. Some installers will run 16" flex to a 3ton HP thinkin thier ductulator is also a flexulator...still not enough air usually
I recently put EfficientComfort.net on my fav's list. They have a nice "rule of thumb" for duct systems. Lots of other good info, also.
For metal supply trunks with 3 tons it says 16". For flex returns it says a 14 and a 12. Oh my gawd
This thread reminds me of a system I found at our local ambulance service....
In order the air goes through the system.....
Face grille, return duct, evaporator coil, filter rack, furnace, supply duct
All electric heat pump
the coil is in the same cabinet as the blower assembly and heater assembly
Air enters coil first, then blower, then electric heat strips
Allows for more even air distribution across coil
Dual fuel system or regular air conditioner with furnace for heat
Furnace then coil
blower is in the furnace
if the coil is put before, the heat exchanger cells would become cold
while in cooling mode. This will cause the inside of the heat exchanger cells
Since alot of furnaces are in attics... the sweating heat exchanger could in fact form enough condensed water to drain onto the ceiling
you also intensify the effect the heat exchanger has on adding heat to the air stream in the summer.
75 degree air going across a 120 degree heat exchanger gains some heat
55 degree air going across a 120 degree heat exchanger gains more heat
(would be equal to 75 degree air moving across a 140 degree heat exchanger.)
technically... the heat exchanger would not be 120 inside it... even though the attic is 120... but the concept remains the same... I just simplified it for discussion
aside from that
I think the real question should be....
how do you find a tech that can do the job correctly
Try contractor locators on various brand name sites....
Carrier,Rheam, and so on
Getting late... will let you look up the other links
Try Nate and ACCA as well
Check with your power and light company... see if they have a heat pump program (we have one through TVA)
I had a , new to my area, Rheem contractor/tech come and look a short time ago. Gave me the "tsk tsk" story. Didn't even charge me for the service call because he felt sorry for us. I mailed him a check anyway. Karma thing, I suppose.
He verified that 2 ton is all I need and that the 14" duct system would work. A 16" return would be better and adding two more registers would be helpful.
Last year I had a, close to my area, Rheem contractor/tech revise my ducting to ~work using the 3 ton, on paper. Still does not make the system right for the house being that it's a bit large. But liveable.
On a side note, both of these contractors seem to think that for our geographic area, forced air is better. But that's another debate.