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  1. #1

    When getting a new furnace, always get a Load Calc?

    Hello everyone, been reading some of the posts here and they have helped alot. My wife and I moved into our house a year ago and the furnace/ac seem to be original to the house which was built in 84. Both are working great so far, but looking to get the furnace replaced as we fear it won't be that long before it gives us problems. Won't be an upgrade as the orginal furnace is already a high effiency furnace. 90% or above according to the home inspector. We plan on replacing the a/c in a few years with a heat pump (recommended by two of the companies since we are on LP, not sure why that makes a difference), but the furnace is the priority now as we live in central Minnesota.

    I got three estimates. One each from a Trane, Ruud, and Bryant dealer. All three companies came recommended. Now I heard that all three brands are good brands and it is the install that will really make the difference. I thought that I would decide between them when one of them performed a load calculation. I thought if they were thorough enough to do that without being asked to, they would be thorough on the install when I don't know what to look for to see if they are going a good job or not. Not one of the companies did one.

    Should this be a red flag or should I have asked for one upfront?

    If this info is needed, we are looking at installing a 95 afue mod furnace. We plan on staying here for a long time and figured the extra few hundred would be worth the comfort. The Ruud and Bryant estimates were comparable. The Trane estimate did not even include the mod furnace, just the 2 stage which was close to the other two modulating.

    We are also going to have an energy audit done here in the next few weeks. Could that help with load calcs or just tell us where to install more insulation?

    Thanks for your time

  2. #2
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    Quote Originally Posted by Nilkc View Post
    Hello everyone, been reading some of the posts here and they have helped alot. My wife and I moved into our house a year ago and the furnace/ac seem to be original to the house which was built in 84. Both are working great so far, but looking to get the furnace replaced as we fear it won't be that long before it gives us problems. Won't be an upgrade as the orginal furnace is already a high effiency furnace. 90% or above according to the home inspector. We plan on replacing the a/c in a few years with a heat pump (recommended by two of the companies since we are on LP, not sure why that makes a difference), but the furnace is the priority now as we live in central Minnesota.

    I got three estimates. One each from a Trane, Ruud, and Bryant dealer. All three companies came recommended. Now I heard that all three brands are good brands and it is the install that will really make the difference. I thought that I would decide between them when one of them performed a load calculation. I thought if they were thorough enough to do that without being asked to, they would be thorough on the install when I don't know what to look for to see if they are going a good job or not. Not one of the companies did one.

    Should this be a red flag or should I have asked for one upfront?

    If this info is needed, we are looking at installing a 95 afue mod furnace. We plan on staying here for a long time and figured the extra few hundred would be worth the comfort. The Ruud and Bryant estimates were comparable. The Trane estimate did not even include the mod furnace, just the 2 stage which was close to the other two modulating.

    We are also going to have an energy audit done here in the next few weeks. Could that help with load calcs or just tell us where to install more insulation?

    Thanks for your time
    Yes load cal. Is always recommed and needs to be done to determine which size hvac system is right for your home.

    If any of the companies you have out have not preformed a load cal. They are guessing on what size is needed! It would be a red flag!!! They are either using square footage per ton rule of thumb or going by what you have already.

    Either way with out a load cal. They don't have anything to back the size of your new equipment and more then lickly will be oversized! So many times I run across this. The contractor is often afraid they will undersize your system. So they put in the Higest heating system.

    If they were to preform a load cal. They would have all the info needed to be able to tell you that your new system is not oversized or undersized. Load cal. On homes is a the only way to ensure your system is propey sized.

    What are the model numbers they have quoted you? What is the size of your home, insulation values in walls and ceiling, window type etc.?

  3. #3
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    Quote Originally Posted by duckman06 View Post
    It would be a red flag!!!
    It depends. It's not that black and white. Furnaces are not made in that many sizes. Sometimes you have to size the furnace by the size of the blower for the AC. I guess in your case they go by the size of your existing furnace. A replacement modulating furnace will be about 35-100% of the size of the old one when the new one has the same input. A load calc in this case is a waist of time.
    It's not like I am against load calc's as I normally always run one, except in cases like yours.

  4. #4
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    Quote Originally Posted by tostaos View Post
    It depends. It's not that black and white. Furnaces are not made in that many sizes. Sometimes you have to size the furnace by the size of the blower for the AC. I guess in your case they go by the size of your existing furnace. A replacement modulating furnace will be about 35-100% of the size of the old one when the new one has the same input. A load calc in this case is a waist of time.
    It's not like I am against load calc's as I normally always run one, except in cases like yours.
    I have to agree, with furnaces it's hard to justify the time spent for a result I already know. In my area 95% of homes will be met with a 60k furnace so I only need to make sure the blower will handle AC/Heat pump.

    Have you considered a ground source heat pump if you are on LP and in a cold region? While the upfront cost may be up to 5X as much as a new furnace, it would also probably pay itself back in less than 5 years, especially if you factor in water heating costs and the replacement heat pump/ AC that is needed down the road.
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  5. #5
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    if all three quotes are ONLY quoting the furnace, not the ductwork, you should ask for a ductwork estimate.
    especially if the ductwork is in the attic.
    90% furnaces did not exist in 84, so it's a replacement furnace at least. and most 90's have stainless heat exchangers and 25 year warranties on them. Propane is a nasty fuel that really requires annual service and cleaning, so look into that.
    Minnesota homes usually have massive insulation, so hopefully that's not an issue, also the ductwork is often in conditioned space, so other than proper distribution, it should not be a concern, but be sure it's checked.
    an air exchange heat pump is all but useless in Minnesota, as the majority of cold weather is beyond a heat pumps ability to heat a home... geothermal is certainly a way to go though.
    The TRUE highest cost system is the system not installed properly...
    The three big summer hearththrobs...
    Mel Gibson
    Dwane Johnson
    The A/C repairman

  6. #6
    What are the model numbers they have quoted you? What is the size of your home, insulation values in walls and ceiling, window type etc.?
    Trane Model VX95

    Rudd Model UPRL-036JEC

    Bryant Model 987MA42080V17

    House is two story with basement, 3,000 sq ft with 251 sq ft of Andersen Windows. The R value of the walls is 17.5 found by an online calculator (6 inch walls, no foam, fiberglass insulation and wood siding). Not sure of the ceiling, Home inspector said the insulation was right at what was recommended.

    Have you considered a ground source heat pump if you are on LP and in a cold region?
    I have, but with the savings I figured over the new furnace it would take more like 20 years to pay off the cost difference.

    90% furnaces did not exist in 84, so it's a replacement furnace at least.
    Sorry the house was built in 86, It is a Dayton fuel trimmer Model 3E438A Serial H642 68721. I can't find anything on it which is suprising since the previous owners kept impeccable records on anything they installed. That also led me to believe that it was original but I could be wrong, but three people told me it was 90% or above.

    an air exchange heat pump is all but useless in Minnesota, as the majority of cold weather is beyond a heat pumps ability to heat a home...
    The heat pump isn't for the winter really. The furnace would kick on when the outside temp goes below 32 degrees which is most of the winter. The heat pump is for the many spring, summer and fall days when the overnight low is in the low 50s and high 40s.

    if all three quotes are ONLY quoting the furnace, not the ductwork, you should ask for a ductwork estimate.
    especially if the ductwork is in the attic.
    The quotes did include ductwork and it is all inside the conditioned space. Nothing in the attic. The only thing mentioned besides changing the ducts to fit the furnace was the Ruud contractor mentioned adding a second return in the basement.

    Thanks again for all the advice

  7. #7
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    Depending on the scope of home energy audit that you're getting you may get a heating and cooling load with that service. With this information you can then compare it to the quotes you have.

    Being educated on the benefits of heating and cooling load information and then using that as a benchmark to qualify a contractor is a good step. Asking them why they did or didn't do one could also bring information into the decision making process.

    A person there at your request to give you a price on replacing equipment is sometimes trained to not confuse you with details you might not understand and that can sometimes overwhelm the decision making process. Asking about those details gives the salesperson the indication that you are interested and informed and want to know something other people might not care about. A majority of the customer's they see are only interested in one thing....... how much is it going to cost.

    At best, heating and cooling load calculations are well educated guesses that are designed to give an answer that is not 100% guaranteed. The information entered is only as good as what can be measured with the rest being assumed or can be closely matched a chart of norms. The dimensional data is always relatively accurate, but the insulating values of walls, ceilings, infiltration and the such are usually derived from charts of options or averages.

    The decisions of what size equipment to use start with those load calculations giving the estimator a starting point. Everything beyond that requires taking into account what is going to make the customer comfortable and be as happy as possible with their decision.

    I always ask a lot of questions all having to do with the customer's expectations of finished comfort when deciding what to offer as options, including the furnace size/capacity. It's not my home and it's not my call on what I think you "have to have", it's my responsibility to make sure that I offer and explain all of the options that I have available that fit your home, situation and expectations.

    A 100% perfectly sized forced air furnace does not exist because the heating need of the home changes constantly. The other thing that changes is the homeowner's expectations during the changing seasons and in some cases even the day of the week or time of day. Big strides have been made with the introduction of the modulating furnaces to better fit these changes, but the comfort of the homeowner is still the driving force of what is best fit in all the conditions, situations and weather. That "best fit" is always going to be a compromise.

    When considering a multi-stage or modulating furnace the duct work should be assessed also. These types of furnaces change the amount of air they move along with the amount of fuel they're burning. If you are used to a single stage (all or nothing) type of furnace you are going to potentially notice differences in how parts of your home heat when the new furnace is in the lower stages of heating. Registers in the home that are a long distance from the furnace may not get enough air to sufficiently heat the room.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  8. #8
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    The Ruud model number you provided is a 16 SEER two stage ultra series heat pump not a furnace.

    How much are you currently paying per year in propane? For a house of that size I would expect it to be in the $3,000-$5,000 per year range. I suggest you take a second look at a geothermal system with that size house and the 30% federal tax credit i would expect a 5 year payback after tax credits if your propane costs are $4,000 a year or more.
    This house saved over $3,000(had $4,200 in propane costs, now has $0 propane but an additional $1,200 per year in electric) per year and is 3,500 sq feet in the Portland Oregon area which is a milder climate than what you are in. This home has a less than 5 year payback and they are more comfortable.

    At least get a bid for it, I think you might be surprised, go to WaterFurnaces website to locate a dealer or any other geo brand and they could probably give your rough pricing and paybacks for your area to see if its worth your time, it may not be the answer, but at least you will know for sure.
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  9. #9
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    Originally Posted by tostaos View Post
    It depends. It's not that black and white. Furnaces are not made in that many sizes. Sometimes you have to size the furnace by the size of the blower for the AC. I guess in your case they go by the size of your existing furnace. A replacement modulating furnace will be about 35-100% of the size of the old one when the new one has the same input. A load calc in this case is a waist of time.
    It's not like I am against load calc's as I normally always run one, except in cases like yours.
    Quote Originally Posted by SkyHeating View Post
    I have to agree, with furnaces it's hard to justify the time spent for a result I already know. In my area 95% of homes will be met with a 60k furnace so I only need to make sure the blower will handle AC/Heat pump.
    Have you considered a ground source heat pump if you are on LP and in a cold region? While the upfront cost may be up to 5X as much as a new furnace, it would also probably pay itself back in less than 5 years, especially if you factor in water heating costs and the replacement heat pump/ AC that is needed down the road.
    I disagree...
    How would you know the proper airflow if no Heat-Calc is done? Answer that!!
    How would you know if the AC is even the right size? Really guys...

    You do a disservice every time a Load Calc is not performed.

    And even, how can you determine the proper fresh-air requirements and even know if a little insulation can help bring down the capacity of a system thereby reducing the annual operating cost...
    Especially here in Minnesota... Really guys. Are we Pros or What?

    How far is Central Minnesota from here?

    I'm really just trying to help you all.

    God speed..

  10. #10
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    Quote Originally Posted by arc8 View Post
    I disagree...
    How would you know the proper airflow if no Heat-Calc is done? Answer that!!
    How would you know if the AC is even the right size? Really guys...

    You do a disservice every time a Load Calc is not performed.

    And even, how can you determine the proper fresh-air requirements and even know if a little insulation can help bring down the capacity of a system thereby reducing the annual operating cost...
    Especially here in Minnesota... Really guys. Are we Pros or What?

    How far is Central Minnesota from here?

    I'm really just trying to help you all.

    God speed..
    I can certainly see your point, but when the majority of homes we do here in Portland are 1,200 to 2,000 sq feet and all furnaces we install have 1,200 CFM 3 ton blowers there is no point, every home will be less than a 3 ton and will not need 60K. Now knowing that the house is 3K sq feet I would do one. I also would do one for any AC or heat pump but I do not for all furnaces and i stand behind that even though it is not the always the accepted practice. If a customer asked(and occasionally they do) I will oblige and do a calculation but I have yet to be wrong making an educated guess on a 1,500 sq foot home that needs a new furnace.
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  11. #11
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    Quote Originally Posted by arc8 View Post
    I disagree...
    How would you know the proper airflow if no Heat-Calc is done? Answer that!!
    How would you know if the AC is even the right size?
    Let's look at my situation two weeks ago. I have a 3.5 t AC that is running just fine and doesn't need replacement, which makes it irrelevant that I don't know if the AC is slightly oversized or not. I will need a 4 ton blower. I have 2 sizes of furnace available, a 80k and a 100k btu. I know that the 80k furnace is large enough as the old furnace heated the house just fine. So for what reason would I run a heat load calculation that will tell me that the optimal size would be a 70k furnace?

  12. #12
    How much are you currently paying per year in propane?
    In the last year we have spent between 1200-1500 on propane. That is the furnace, dryer, gas fireplace and with a gas leak at a cracked fitting at the outside regulator that was just found 2 months ago.

    How far is Central Minnesota from here?
    We live just outside Saint Cloud.

    So what I am taking from this is to ask one of the contractors to perform a load calc and ask the others why they didn't perform one. Also it might be helpful to wait till after the energy audit. Really looking forward to that as I only recaulked half the windows and I want to compare the windows during the blower door test.

  13. #13
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    Quote Originally Posted by tostaos View Post
    Let's look at my situation two weeks ago. I have a 3.5 t AC that is running just fine and doesn't need replacement, which makes it irrelevant that I don't know if the AC is slightly oversized or not. I will need a 4 ton blower. I have 2 sizes of furnace available, a 80k and a 100k btu. I know that the 80k furnace is large enough as the old furnace heated the house just fine. So for what reason would I run a heat load calculation that will tell me that the optimal size would be a 70k furnace?
    It's simple because you need to! What if the a/c system is oversized? The customer may not be aware of this and might decide to go ahead and upgrade the entire system.

    If I had a dollar for everytime that has happened I would be rich. Example lets say the home only needs a (3) ton a/c system? If so then you could look at 60,000-80,000 btu furnace to heat the home along with a (3) ton system to cool it. If the load was preformed you would no for sure what size heating and cooling system is needed along with the proff to back it up!

    I am just saying that load cal is always good to run to ensure you are installing the best sized system for the home!

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