Page 1 of 2 12 LastLast
Results 1 to 13 of 20

Thread: Three Fuel ?

  1. #1
    Join Date
    Jun 2007
    Location
    Bucks Co PA
    Posts
    364

    Three Fuel ?

    Is it possible to have a heat pump with a heat strip plus furnace??

    Here is what I'm thinking; If I could have a heat pump w/heat strip, so in defrost mode the strips would come on down to a temp of 32*, where the heat pump and strip is locked out so the furnace would take over.

    Is this possible ??

    It seems almost a waste to have a furnace kick on for just a few minutes during defrost. How much heat does a furnace even create during defrost?
    .

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    Varies with the lenght of defrost cycle, and the BTU of the furnace.

    Its possible if you have room for the strip heaters. And can find someone thats good with low voltage wiring.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Jun 2008
    Location
    west point, ga.
    Posts
    328
    I've done it

  4. #4
    Join Date
    Sep 2002
    Posts
    12,651

    That's exactly how I'm setting up mine -

    No way I'm firing a 93% gas furnace for every defrost.

    I going to try to not use any heat during defrost as I plan the chnage-over for a fairly mild ambient. But if that is uncomfortable - I have ten KW of electric heat ready to go.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  5. #5
    Join Date
    Jun 2008
    Location
    west point, ga.
    Posts
    328
    Quote Originally Posted by Poodle Head Mikey View Post
    No way I'm firing a 93% gas furnace for every defrost.

    I going to try to not use any heat during defrost as I plan the chnage-over for a fairly mild ambient. But if that is uncomfortable - I have ten KW of electric heat ready to go.
    Dude different folks different strokes.Besides down here you don't have that cold of a winter.For some reason that is what the customer wanted so that is what he got.I really didn't see the point but I get paid by the hr.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    Quote Originally Posted by Poodle Head Mikey View Post
    No way I'm firing a 93% gas furnace for every defrost.

    I going to try to not use any heat during defrost as I plan the chnage-over for a fairly mild ambient. But if that is uncomfortable - I have ten KW of electric heat ready to go.
    What do ou considr a mild change over ambient..
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  7. #7
    Join Date
    Sep 2002
    Posts
    12,651

    Part of the problem is the on-delay time

    With a 90+ furnace cycling on - it's probably the better part of five minutes before it is producing any noticable amount of heat. And by then the defrost is likely over anyway.

    The electric heat elements are almost instant-on.

    For 'mild ambient change-over' I have in mind maybe thirty or thirty-five degrees. But like so many things in my Life there will, no doubt; be some tweaking involved.

    Of course; I do live ever in the hope that beenthere will come to my design-rescue, tell me what to do for the best, and so spare me the tedious agony of overcoming my own fumbling attempts at empirical sorting. <g>
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    Don't know if I ever seen a 90&#37; furnace take 5 minutes to put out heat.
    2 to 3 minutes though.

    Best set up. A unit with On demand defrost. Cuts down on those needless defrost cycles.

    You must have a tall basement to get a heat kit in your plenum and be far enough above your coil.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
    Join Date
    Sep 2002
    Posts
    12,651

    OK - le's call it 2.5 minutes then

    And let's say that the defrost time on the HP will be maybe five to ten? So do we really want the furnace starting and then stopping in five or ten minutes? I don't.

    Aren't all heat pumps using 'on-demand' defrost now?

    My cellar isn't all that tall - but it is sixty feet long.

    PHM
    ---------


    Quote Originally Posted by beenthere View Post
    Don't know if I ever seen a 90% furnace take 5 minutes to put out heat.
    2 to 3 minutes though.

    Best set up. A unit with On demand defrost. Cuts down on those needless defrost cycles.

    You must have a tall basement to get a heat kit in your plenum and be far enough above your coil.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    Lot of HPs still use time and temp defrost conttrols.

    6 one way, half a dozen the other.

    May not get to full efficincy in 5 minutes. But the furnace putting heat into the evap coil, also shortens teh defrost time, by heating up teh OD coil quicker.

    Electric strip after the coil, 100&#37; efficiency right aways, but adds no heat to the ID coil, so the OD coil takes longer to defrost.

    Which method is better, will depend on your rates, winter OD ambient conditions.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  11. #11
    Join Date
    Sep 2002
    Posts
    12,651

    so how about if I put the strip before the coil?

    Wouldn't that give me the best of both concepts?

    PHM
    ---------

    Quote Originally Posted by beenthere View Post
    Lot of HPs still use time and temp defrost conttrols.

    6 one way, half a dozen the other.

    May not get to full efficincy in 5 minutes. But the furnace putting heat into the evap coil, also shortens teh defrost time, by heating up teh OD coil quicker.

    Electric strip after the coil, 100% efficiency right aways, but adds no heat to the ID coil, so the OD coil takes longer to defrost.

    Which method is better, will depend on your rates, winter OD ambient conditions.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  12. #12
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,171
    Yes it would.

    How practical it is to do it. I guess would be dependant on the install set up.

    But should for all practical purposes give you shorter defrost cycles, and tempered air temps during those defrost cycles.

    Let us know how it works in the real world. Cause it does look good on paper.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  13. #13
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by Poodle Head Mikey View Post
    Wouldn't that give me the best of both concepts?

    PHM
    ---------
    all that dust burning off the heaters at the beggining of the season getting impacted in the evaporator



    .

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event