Page 1 of 3 123 LastLast
Results 1 to 13 of 30
  1. #1
    Join Date
    May 2009
    Posts
    196

    Picking up the pieces after a botched install

    Over two years ago we had a factory authorized dealer replace our dead furnace with a heat pump system with electric backup. This work involved reducting all rooms in the lower level. The new heating system isn't able to heat the lower level above the mid 60s. After two years of reminders, the dealer walked away from the job with the excuse that the house can't (!) be heated.

    After consulting with 3rd party experts and doing a load calc, it appears that the new ducting doesn't move enough CFM for heat pump use and the heat pump is undersized for the entire house. If the ducts were adequate, the HP balance point would be around 40 and the remaining 47,000 btu needed to heat the house at the design temperature for this area would need to come from the electric backup. The electric backup is only capable of 34Kbtu (10kw). To lower the balance point to 32 would mean replacing the existing heat pump with a 5 ton unit.

    What should I be asking for when getting fix-up bids from other contractors? I've come up with four options but am looking for advice on which way to go next.

    1. Fix ducting + replace the existing 3 ton heat pump / coil with a 5 ton heat pump / coil. This is probably beyond my budget.

    2. Fix ducting + upgrade heat strips to cope with design temperature? If I do this, I'll be paying for 3,500btu of electric heat for most of the heating season and 47,000btu (!) on design days. Expensive.

    3. Fix ducting + install propane furnace & ditch the heat strips.

    4. Dedicate the existing HP and heat strips to the main level and install something else to serve the lower level. The existing HP is about the right size to heat the upstairs level down to design temperature w/o any electric backup. The lower level requires about 24,000btu at design temperature and about 9,500btu for most of the heating season. I'm considering three options for a system for the lower level:

    4a. Electric baseboard heaters for the lower level. Will mean paying for between 9,300btu and 25,000btu of electric heat through the heating season.

    4b. 2 ton heat pump for lower level w/ new duct work. House electrical service is barely enough to cope if both HPs defrost at once while every other high load electrical device (stove, water heater, oven) is on at the same time.

    4c. Hydronic propane boiler system w/ radiators. The boiler would also replace the electric water heater.

    Comments?

    Budget is definitely an issue but I'm prepared to pay more up front in exchange for lower operating costs provided the payback time no more than 5yr or so.

    Thanks.

  2. #2
    Join Date
    Apr 2008
    Location
    TEXAS
    Posts
    1,701
    the cheapest thing to do would be to upgrade the heat strips. this would also buy a little time to weigh your options. jmho.
    "When the people find they can vote themselves money,that will herald the end of the republic" - Benjamin Franklin

    "Government is not reason, it is not eloquence, it is force;like fire, a troublesome servant and a fearful master. Never for a moment should it be left to irresponsible action"- George Washington

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    You don't give real any info about your house.
    Other then it has 2 levels.

    How big is each level.
    Are both levels above ground.
    Where are you located.

    How old is it.
    Have any improvements been made to its air tightness, and or insulation(both can be big savers on heating cost).

    Also, how does the 3 ton unit do in cooling?
    Are you looking to have a heat pump sized to the heating load instead of the cooling load?

    Was an actual load calc done now. Or just another guess by sq ft.
    Contractor locator map

    How-to-apply-for-Professional

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

  4. #4
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    I personally would consider re-useing the existing system on the upper level IF...IF... the load calcs say it's sazed correctly for heating and cooling. Then install a new properly sized system to serve the lower level and make sure the ductwork gets sized correctly this time.

    It sounds like a single system would need to be zoned to work correctly in this home.

  5. #5
    Join Date
    May 2009
    Posts
    196
    Quote Originally Posted by beenthere View Post
    You don't give real any info about your house.
    Other then it has 2 levels.
    I've done an actual load calc. 60kbtu at the 10 degree design temp for this area. Outside of the coldest weeks, most of the winter sees temps in the 40s and a heat loss of ~33kbtu. Outside temps only rise above the mid-high 60s for six to eight weeks a year--I need some heat every day for ~9 months a year.

    There is very little need for cooling here except to remove solar loading for a few hours a day during a handful of days a year. It makes sense to size the HP for heating only.

    The lower level is partially in-ground and is 700sq ft. The upper level is 900sq ft and is completely above grade.

    The house is about 25 years old. Measured air infiltration (blower door test) is 0.5 ACH. All the low hanging insulation fruit has been taken care of; cutting heat losses further would cost around $2 per btu to a maximum of about 11,000btu of potential improvement. Getting more than 11,000btu would mean extreme measures like reconstructing the outside walls.

    My current heating system will fall behind by 13,000btu at 10 degrees.

  6. #6
    Join Date
    May 2009
    Posts
    196
    Quote Originally Posted by motoguy128 View Post
    I personally would consider re-useing the existing system on the upper level IF...IF... the load calcs say it's sazed correctly for heating and cooling.
    The HP alone is the right size to heat the upper floor down to 31 degrees. At 10 degrees, the combined output of the HP and heat strips is oversized by 16kbtu. The heat strips are two stage but I don't know the split point. I'm hoping its 50/100 as 50% output + the heat pump output would match the upper floor's heat loss exactly at 10 degrees.

    Cooling loads are negligible in this climate. A unit sized to cool wouldn't be big enough to heat.

    Then install a new properly sized system to serve the lower level and make sure the ductwork gets sized correctly this time.
    Much easier said than done. None of the FADs who bid on the first job would even do a load calc....

    It sounds like a single system would need to be zoned to work correctly in this home.
    If the lower level ducting was adequate, could the temperatures be equalized by continually circulating a few hundred CFM between the two levels? The worst case spread is about 10 degrees.

  7. #7
    Join Date
    Jun 2005
    Location
    Near Chicago, IL
    Posts
    3,317
    Your design is short on paper.

    A 3T HP = maybe 36k BTU of heat around what, 60* F? Heat output goes down as outdoor temperature goes down. Your 10kW strip is 34k btu.

    So, at best, you have 70k btu of heat available somewhere around 60* F... and less as it gets colder. Just guessing here, but you *might* have 18k btu of HP available at 10*F if the rest of your system is perfect (and it isn't)... so, 18k btu + 34k btu= 52k btu.

    60k BTU at 1600 SF with a winter design of 10* F? Do you leave the door open or something? Your partial lower level has little heat loss.

    I have 1400 SF on a slab with a winter design of -1*f. HVAC-Calc put the loss at 60k btu. Walls have R9 and the ceiling isn't much better... new '80's siding has a little bit of foam under it... original single pane windows with storms... built in or near '67. Blocked off a HX cell on a 100k 80% furnace, so have *at best* calculated (not measured) 60k net output. The furnace still cycled at double digits below zero. Real world experience here.

    You need to re evaluate your load calc.

    You need to get that ductwork done right.

    Double check the specs on that heat pump and evap coil combination.

    If you can't move the air, you won't get the btu's.

    It should work.

  8. #8
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,325
    What kind of windows does this house have?

    The greater the temperature difference between indoors and outdoors, the greater offender windows are for becoming the lion's share of heat loss from the structure to the great outdoors. Next in line would be infiltration (leakage). If you have a hard time keeping your house humid enough when the air is dry and cold outdoors, you have a lot of that air leaking into the house.

    Make the house easier to heat, it will cost less to heat. Make the house retain its heat better, your comfort will be better. Address issues with your heat pump AND look for other parts of your house that could be stealing your heat away.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    Quote Originally Posted by neophytes serendipity View Post
    Your design is short on paper.

    A 3T HP = maybe 36k BTU of heat around what, 60* F? Heat output goes down as outdoor temperature goes down. Your 10kW strip is 34k btu.

    So, at best, you have 70k btu of heat available somewhere around 60* F... and less as it gets colder. Just guessing here, but you *might* have 18k btu of HP available at 10*F if the rest of your system is perfect (and it isn't)... so, 18k btu + 34k btu= 52k btu.
    No. A 3 ton heat pump would have around 36,000 at 47°OD temp. And around 18,000 at 17° OD temp.
    Contractor locator map

    How-to-apply-for-Professional

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

  10. #10
    Join Date
    Jun 2005
    Location
    Near Chicago, IL
    Posts
    3,317
    Quote Originally Posted by beenthere View Post
    No. A 3 ton heat pump would have around 36,000 at 47°OD temp. And around 18,000 at 17° OD temp.
    Ok, but the design is still short on paper, unless my math is wrong...

    36,000 (heat pump) + 34,000 (strips) = 70,000 btu at 47* ODT

    18,000 (heat pump) + 34,000 (strips) = 52,000 at 17* ODT

    So, if the OP *really* needs 60,000 btu of heat at 10*F ODT... it isn't there... assuming the heat pump is operating at 100% capacity.

    Did I miss something?

  11. #11
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,325
    Quote Originally Posted by neophytes serendipity View Post
    Ok, but the design is still short on paper, unless my math is wrong...

    36,000 (heat pump) + 34,000 (strips) = 70,000 btu at 47* ODT

    18,000 (heat pump) + 34,000 (strips) = 52,000 at 17* ODT

    So, if the OP *really* needs 60,000 btu of heat at 10*F ODT... it isn't there... assuming the heat pump is operating at 100% capacity.

    Did I miss something?
    A heat loss calculation would be interesting to see if the house is close to losing 60,000 btu per hour at 10°F outdoor temperature. Saving energy isn't the only motivating factor for improving a structure's ability to retain its conditioned air, summer or winter. Human comfort is why we do all this, anyway. A house that is tight only helps in that regard.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  12. #12
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    Quote Originally Posted by neophytes serendipity View Post
    Ok, but the design is still short on paper, unless my math is wrong...

    36,000 (heat pump) + 34,000 (strips) = 70,000 btu at 47* ODT

    18,000 (heat pump) + 34,000 (strips) = 52,000 at 17* ODT

    So, if the OP *really* needs 60,000 btu of heat at 10*F ODT... it isn't there... assuming the heat pump is operating at 100% capacity.

    Did I miss something?
    The question is. Does the house really need 60,000BTUs of heat.

    Other wise. Your math is correct.

    A lot of houses around here with a 3 ton heat pump can get away with only 10 KW, many need 15 KW of strip.
    Contractor locator map

    How-to-apply-for-Professional

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

  13. #13
    Join Date
    Jun 2005
    Location
    Near Chicago, IL
    Posts
    3,317
    Well, at a -1*F design temp, I don't need the 60k btus of heat... and all of my house is exposed- no half basement here.

    I bet if the ductwork was fixed the OP's system would work.

Page 1 of 3 123 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