-
Variable speed heat pump with older oil furnace as a backup
I recently purchased a home built in 1997. All the HVAC is original, and I'm considering my options for replacement to minimize cost and maximize efficiency. (Duh. )
The home has two American Standard A/C condensers (a 3 ton and a 4 ton) as well as two American Standard oil fired furnaces. (Home has two floors and a walk out basement - 4 ton for basement/1st floor, 3 ton for second floor.) The furnaces are running about 84% efficient, so I don't think I'll replace them until they konk out.
I believe I've settled on replacing the existing cooling units with variable speed heat pumps (probably the American Standard Platinum 20), as this would take me from ~12 SEER in the summer to ~21 SEER, and remove the need for probably 70-80% of my oil usage in the winter. (I live just north of Boston.)
My HVAC tech think that a variable speed heat pump can't be used in conjunction with my existing oil furnaces. He said I'll need to go with a two-speed unit instead, or not use the furnaces as a backup.
Can somebody explain why this would be the case? (He doesn't seem willing or able to.)
-
-
The vs 18 and 20 seer units are special and require matching indoor units, I recommend the 18 with a vs electric air handler for the best performance and efficiency for the money
-
Originally Posted by
ksefan
The vs 18 and 20 seer units are special and require matching indoor units, I recommend the 18 with a vs electric air handler for the best performance and efficiency for the money
Ah, I see. Are there any other variable speed heat pumps that can be matched with a ~1997/1998 American Standard oil furnace?
-
A variable speed indoor blower is part of the matched system and is necessary for anything 2 staged or above. You're basically looking at no better than 14 seer tops with those old furnaces.
You're also making a false assumption that's common even in the trade: because the seer rating is higher, that heating efficiency will also be higher. This is not true. The seer rating applies only to cooling. The HSPF is the heating rating and most 14 + seer heat pumps have an 8.5 - 10 HSPF.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
-
You need to find a reputable/experienced dealer and have them evaluate what you've got there including duct system/air flow. I can't think of any variable speed systems that will "match" up to an older oil furnace and let you achieve any type of actual efficiency. They might be advertised as 20 SEER, but that's generally with a new matched air handler/blower coil system and never an older oil furnace. Be careful putting any A coil with a plastic or fiberglass drain pan on these oil furnaces......it'll melt them!
-
Post Likes - 1 Likes, 0 Dislikes
-
Remember, all the efficiency ratings you see are given under ideal conditions. Actual will vary based on the install and what equipment it's matched to.
“I haven’t failed. I’ve just found 10,000 ways that won’t work.” - Thomas Edison
“It’s not whether you get knocked down, it’s whether you get up.” - Vince Lombardi
"In this house we obey the laws of thermodynamics" - Homer Simpson
Local 486 Instructor & Service Technician
-
So I take it that it's not possible to replace the air handler and blower coil with the one that matches the variable speed heat pump while also allowing the oil furnace to provide backup heat?
I'll certainly get another HVAC pro in to evaluate - I was just trying to educate myself as much as possible.
-
You could install an after market ECM motor in the the oil furnace and that may take you from 14 up to 15 seer, but you still won't be able to use a variable speed or 2staged heat pump. This, by the way, would not be a bad choice and could still save you a lot on oil.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
-
No, that would not be a feasible or recommend option.
If you want a fossil fuel hybrid, get a single or two stage heat pump with matching coil and install that. Efficiency will not be 100% of the ratings, but you'll save on oil. And you will not need communicating controls like for a variable speed unit.
“I haven’t failed. I’ve just found 10,000 ways that won’t work.” - Thomas Edison
“It’s not whether you get knocked down, it’s whether you get up.” - Vince Lombardi
"In this house we obey the laws of thermodynamics" - Homer Simpson
Local 486 Instructor & Service Technician