Major System re-design

Discussion in 'General Discussions' started by hokie, Mar 21, 2011.

  1. hokie

    hokie New Member

    I have a 3 T unit serving about 1600 square feet of leaky old stone house. Although there was an energy audit and blower door test, my system seems to have been generally designed according to a rule of thumb, like "old stone houses around 1600 sqft require a 3T system." I got 3 quotes from installers, and all of them took the energy audit information and propsed a 3T system.

    This winter, we spent a nearly all of our time below 40 degrees cycling between 2nd stage and auxiliary electric heat. Our electric bills were large.

    We have been going back and forth with our installer for several months on a fix. W purged the loop - no improvement. They came out and did another energy audit - blower door, IR photos, etc. - and came up with a large winter ACH number - almost 2 and an 85,000 BTU/hr heat loss. Yes - our house leaks. So now, instead of a 3T system, they would like to upsize us to a 5T and have asked us to pay for additional loop, which is going to be expensive on our particular piece of property.

    Does this seem crazy to anyone else out there? Yes, our house leaks, but we have spent significant money tightening things up since the first audit, with little effect on the ACH number. We plan on doing more to tighten up the building in the future.

    I see people on here with 3T-4T units serving 3,000 sqft of old house. I'm trying to figure out if the 5T proposal for 1600sqft makes sense in ANY context.

    They would also like to size the loop field at 6T for a 5T unit - an addition of 2T of loop.

    I've looked at the load calculations and they seem to make sense - although I'm not an expert.

    I'm also a little worried about the system's ability to cool the house in the summer. With the 3T unit last summer, we struggled to cool the second floor because the first floor has thick stone walls and is always cool (i.e. the A/C doesn't often run). If I make the unit larger, won't this exacerbate the problem?

    Help! Need some feedback!!
  2. tstolze

    tstolze Member

    I have no idea what would be involved but my focus would be on making the house work with the current unit. You will spend it once instead of paying the additional operating cost of a larger unit year after year. I would think this would make the house more comfortable year round also.
  3. hokie

    hokie New Member

    a note on ACH

    I quizzed the designer on the effect of reducing our air changes per hour (ACH) to around 1, which I think is a pretty reasonable number for a stone house of this vintage (1860's). He said he re-ran the numbers and that he would still suggest a 5T unit based on the data.

    I agree with you on paying once vs. paying every winter, but if we make the improvements and still need a 5T unit, that would be a moot point. Don't get me wrong - we have made improvements to the envelope and will continue to chip away.

    Does that first paragraph make sense? Could I cut my ACH in half and still need a 5T unit?
  4. Designer_Mike

    Designer_Mike Member

    I would think you could spend a LOT of money improving the efficiency of the house instead of throwing more BTU at it and be money ahead.

    Tightening it up will cost you once.

    Enlarging the HVAC system and feeding it electricity will cost you more EVERY month until you give in and seal it up.

    Adding a more affordable auxilary heat source combined with more insulation may be the most affordable option.

    I understand it might not be easy but few things are.
  5. tstolze

    tstolze Member

    I did not see what area you live in, that may help the professionals that step in to give you a definite direction. Obviously we are in two different homes, mine is 17 years old and I believe I have done a decent job of sealing the envelope, although I still think it can be much better. Our home is just under 1200 sq/ft, we have a 2 ton unit and never hit the auxiliary strips this winter, even just below zero. We are located just west of St. Louis, MO. If your home was "sealed up" in my opinion your unit should handle the load. Unless of course you are way north... ;)
  6. hokie

    hokie New Member


    I'm in northern Delaware. Not terribly cold - maybe 15 days where temp dipped below 20.

    Any reason why my hvac guys would be eager to give me 5T instead of helping me to seal the place up? It's going to cost them more to to the re-design - by a longshot.
  7. moondawg

    moondawg Member

    When you've got a toolbox full of hammers, everything looks like a nail.

    I'm guessing your HVAC guys know HVAC real well, and may not know much about sealing up and insulating a building.

    They KNOW that throwing a 5T unit at the problem will keep you warm.... but they aren't *exactly* sure what can be done to reduce the heating load of the building.

    Just a guess.
  8. Designer_Mike

    Designer_Mike Member

    I would think they will make a LOT more $$ by installing a 5T system than by helping you figure out where the heat is going.

    I'm not sure about your system, but the change could cost you BIG TIME.
    Ductwork will most likely be undersided $$ and working in an old house $$$
    Purchasing the 5T unit $$
    enlarging your ground loop $$$
    new flow center $$
    improved controls $

    I wouldn't be surprised if they tell you it will cost in excess of $20K to upgrade to a 5T system. (just an educated guess no knowing your home)
    That would buy a lot of new windows, insulation, and siding.
  9. zach

    zach Member Forum Leader


    I'd give a hard look at reducing your building load. When you say, 'they came out and did another energy audit....", who is they?

    If they is the HVAC contractor, I'd get another opinion. Having just sat through the BPI Building Analyst training I can tell you there are usually cost effective ways to air seal an old house.

    Get a second or third opinion using a BPI trained analyst. One of the most effective places to air seal is the rim joist down in your basement or crawlspace if you have one. Might even be a way to spray foam your interior basement walls. Do you know where your leaks are? A reputable analyst should have provided that in his report with suggestions and estimated costs for repair including payback.


  10. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    I would like to know the heat load as opposed to what size heat pump the designer suggested.
  11. ChrisJ

    ChrisJ Active Member Forum Leader

    With an 85000BTU heat loss, is 5 ton even enough.

    Original post said 85000.

    Last edited: Mar 22, 2011
  12. hokie

    hokie New Member

    Yes, HVAC guys calculated heat loss of 85,000 btu/h.

    Designermike - I guess we are lucky because the HVAC contractor is planning to eat the cost of most of the work (changing the unit out, increasing duct size, etc). They are asking us to cover some of the cost of increasing the loop size. Their logic is that we would have been responsible for that cost had the equipment been sized properly to start with.

    We have done some things to seal up the house already. We sprayfoamed the crawlspace - which improved things, but there still seems to be some leakage around the edge of the floors. One of the major issues with the house is that most of it is bare concrete (concrete or stucco over stone) which, although very thick, apparently has very little R-value. We really can't do anything about this as it would completely change the nature of the house to try and insulate the interior walls. We could definitely do more to improve the air leakage. There are some low-hanging fruit.

    The way the HVAC company explains it, though, is that through air sealing, we could reduce our air changes per hour to a very reasonable 1.0 (from the current 1.98)and still (according to them) need a 5T system according to heat loss calculations. I can't remember the number they came up with, but I think it was roughly 70,000 btu/hr if we reduced the leakage. More than 1/3 of that comes from the walls.

    Does this make sense?
  13. Designer_Mike

    Designer_Mike Member

    So you need to jack-hammer all the concrete and stucco off the house, put in 6" of insulation, and then put stucco back over the outside:D

    I'll be right down with my jack hammer ;)

    Then you can bore holes through the stone and run radiant heating pipes through the walls and you'll be good to go!
    Sounds cheap to me :rolleyes:
  14. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader

    Calm down

    I am on your side. I will be going past you to DC soon. I am trying to take the White House geo.

    I am too old to spend three days in the trenches. I did not bring a camera cable so no real pictures of me working.

    Mike, I got you an email about size this am. Do you have my cell number?

  15. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Load a little under 70 might do well with a 4 ton vs 5 depending on electric rates.
    Sounds like your installer has offered an equitable cost division.

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