Load J calc not matching bids

[grizzzlle]

Hello. I have been reading this site for last couple months and it has helped alot. I am currently getting bids to have my oil furnace replaced with a heat pump. The trouble I am running into is the load calc that companies are performing is not matching what people think belong in my size of house. It is causing companies to give me conflicting information.

To start with my house totals right at 2000 square feet. The main floor is 1300 square feet with poor insulation characteristics. The second floor is 700 square feet and just recently completed so it is up to current code on insulation. The problem is every contractor that has come out to bid on installing a system takes a guess that I will need a three ton system. Once a load calc is completed the numbers say I need a much larger system. I my self have done calc and get btu needs around 52000 for heating. My load calc that I have done match those calcs that other companies have done. Problem is some contractors are saying it can't be correct so they will bid three ton systems. Some contractors are going by the numbers and bid a five ton system with dual pump. The thought is if my house does not need five ton then the unit will only run on less of a power draw. My question is how accurate is the j load calc and should I allow a large fudge factor when comparing bids? As it stands the companies that have given me bids are very close on every aspect accept what size unit to go with. Thanks for any advice and help in advance.

James

[jimj]

My question is how accurate is the j load calc
Done properly a manual j is accurate, done with fudge factor and bogus input I can make it say whatever you would like!

[heaterman]

First off, congrats on the Manual Js. Now, as far as how accurate, in most programs there is a fudge factor built in so while it may lean slightly toward over sizing it won't be much. I am assuming in your area, heating loads normally out weigh cooling loads. All of the programs should base their calculation on design temps for your geographical location. With heat pumps, this is where the rub comes in, at least in my area which happens to be heating heavy. It is not unusual for the heat loss to call for 60 or 70k of heat but be in the 30-36k range for cooling. So, 5 ton needed for heat 2.5 ton needed for cooling. What to do? Typically we might go heavier on the cooling by half a ton but that's about it so there is going to be a short fall on the heating end. We make this up with aux heat normally a fossil fuel back-up or resistance heat. Outside of that, then you start looking at multi stage or multi unit set ups to meet the needs from both aspects without being grossly over or under sized for either heating or cooling. The only thing you can be certain of is if you don't come close to matching your calculated heating needs with your selected equipment's output, your will be undersized once the actual temperature goes below what you equipment can put out and it won't keep up. The contractors that are doubting the results of the manual J calcs, what is their basis for this? What else do they suggest other than under sizing the equipment without adding make up capacity in the form of auxiliary heat? What were the heat gain calcs for cooling? Do you have plans to upgrade the structural envelope of the older portion of the house? This will affect the calcs and sizing down the road.

[grizzzlle]

I live in the country so my only options for heat other than a heat pump ( electric) is oil or propane. After talking with several hvac companies they did not recommend either do to cost. The contractors theories are that they have installed units in similar situation and those house did not need that large of a unit. I am not planning on doing any upgrades to insulation within in the walls for two reason. First an energy audit said for the cost of adding insulation compared to the pay back time it would not make sense. My biggest bang for the buck was to go away from oil. Also after talking with a couple contractors that I run into while doing my daily job there was concerns about the house not being properly sealed against vapor from the inside or possible leaks on the outside in the future. According to the home builders I could run into aproblem of creating mold or rot by changing how the house has "breathed" for all these years. The thought was using a smaller heat pump since my ac numbers are much lower (don't remeber) and using heat strips when needed. After all the reading I have done heat strips sound like an expensive way to heat if I was to need them.

[tlb]

would you allow a large fudge factor on your taxes no in our area maual j's are used to size for the cooling load then use aux heat to make up the difference on the heat side i would at most go 1\2 ton larger than what the load calls for in the summer if you have a unit that is grossly oversized your unit will shortcycle also run the risk of having humidty\moisture problems if you size your HP for heating load it is always going to be oversized in our area anyway

[heaterman]

I think a two stage unit may be your best option since you are set againt duel fuel. Being grossly over sized for cooling is not a good thing. Because of the heat loss factor, aux. strip has the potential to be costly. To be honest, we have a lot of older homes in our area and to have a calculated heat loss in the 53,000 btu range for a house your size would not be unusual. The heating design temp for our area is 5

[grizzzlle]

Thanks for the information and opinions. I am trying to compare the cost of running a larger heat pump with a two speed pump (or a unit that has two pumps) but am having trouble tracking down power usage between the two speeds. Does anyone have a rough idea how much power a average two speed pump would usewhile running on the slower speed or smaller pump vs running at full power. Any rough idea helps. I am looking at multiple manufactures and just trying to get an idea on running a large pump vs small pump with heat strips.

Thanks

[seatonheating]

Thanks for the information and opinions. I am trying to compare the cost of running a larger heat pump with a two speed pump (or a unit that has two pumps) but am having trouble tracking down power usage between the two speeds. Does anyone have a rough idea how much power a average two speed pump would usewhile running on the slower speed or smaller pump vs running at full power. Any rough idea helps. I am looking at multiple manufactures and just trying to get an idea on running a large pump vs small pump with heat strips.

Thanks


2 stages are for comfort and humidity control, of course humidity isn't a problem in Portland (born and raised myself).

With your situation sizing will be critical to ensure a good economical balance point is established along with a good comfort balance point. Find a contractor that knows how to calculate both these OD temperatures.

Portland area is an awesome area for high efficiency heat pumps!!

[KCA]

Another native Oregonian here. :) I live on the East Coast now, though.

Anyway, on a 2-stage unit, both stages are similar in what goes in vs. what you get out. For instance, here is some Goodman data.

http://www.goodmanmfg.com/Portals/0/pdf/SS/SS-DSZC16.pdf

If you look on pg. 24, you can see COP for low and high stage for different systems. The COP is how much you get out for how much you put in (higher number is better). This is only for the heat pump portion of the heat. If the heat is supplemented with resistance heat, the average COP will be lower. Pure resistance heat (electric furnace, electric baseboard, etc.) will have a COP of 1.

[jimj]

Thanks for the information and opinions. I am trying to compare the cost of running a larger heat pump with a two speed pump (or a unit that has two pumps) but am having trouble tracking down power usage between the two speeds. Does anyone have a rough idea how much power a average two speed pump would usewhile running on the slower speed or smaller pump vs running at full power. Any rough idea helps. I am looking at multiple manufactures and just trying to get an idea on running a large pump vs small pump with heat strips.

Thanks


Here ya go.

[seatonheating]

Another native Oregonian here. :) I live on the East Coast now, though.

Anyway, on a 2-stage unit, both stages are similar in what goes in vs. what you get out. For instance, here is some Goodman data.

http://www.goodmanmfg.com/Portals/0/pdf/SS/SS-DSZC16.pdf

If you look on pg. 24, you can see COP for low and high stage for different systems. The COP is how much you get out for how much you put in (higher number is better). This is only for the heat pump portion of the heat. If the heat is supplemented with resistance heat, the average COP will be lower. Pure resistance heat (electric furnace, electric baseboard, etc.) will have a COP of 1.

Yep, minimizing the time that the electric heat comes on coupled with minimizing heat pump oversizing. It is a delicate balancing act that only the top contractors can get right.

[beenthere]

Size the heat pump to the cooling load, not the heating load.

Very doubtful that your current duct work can handle 2000 CFM that a 5 ton heat pump would need.

[grizzzlle]

Thanks to everyone who has provided information. It has brought up a couple good points that I need to rethink and a couple things I was overlooking. As beenthere mentioned I dont think my duct work could handle the extra air flow. One of the companies that came out and bid on the project spefically made the statement that my duct work would impact what size unit, matched to the inside fan, they would be able to recomend to me. Again thanks for everyones time and help.

James

[SkyHeating]

Have you called us at Sky Heating yet? I have noticed in my experience that many people "pretend" to do Manual J's. I have come against some HVAC contractors that measure windows and doors just for a horse and pony show and then make up a number and some that do very accurate assesment. If you would like to call us we can do a full Manual j and properly size your house and give you recomendations for how to seal up or how to get your house to work with a smaller unit. While I do make more money on a 5 ton, I would rather have you insulate and install a 3 ton if it makes more sense and sometimes it does.

-Travis
Owner Sky Heating & AC

[grizzzlle]

Skyheating. Thanks for your offer to help but I have already made a verbal commitment with a heating company. A little more information about why I started this thread. I know some of the companies were doing manual j calcs since they would spend the time to measure my house call me a week later and tell me my heat gain and lost numbers. The numbers were close to what I was getting using the HVAC4 program. At that time what I did not understand was how to size a heat pump to those numbers. The manual j said I needed a three ton system for cooling but five ton for heating. As I learned from members of this site (and from re reading the manual from the program) you should match the cooling ton and use heat strips to make up any additional heat requirements. A couple companies wanted to sell me a five ton two speed heat pump. What I was told by the people doing the bid is during the summer the unit would run in slow speed for cooling needs and come winter it would run in the second speed if needed for the extra heating ability. After looking at the bids and talking with a few other people I think the companies that gave me quotes for five ton systems event way over board with what they offered. 5 ton 21 seer electronic air cleaners big dollar maintenance contracts shiny things with bells and whistles sort of stud. Needles to say I did not go with those companies. Thanks for your time.

[seatonheating]

Skyheating. Thanks for your offer to help but I have already made a verbal commitment with a heating company. A little more information about why I started this thread. I know some of the companies were doing manual j calcs since they would spend the time to measure my house call me a week later and tell me my heat gain and lost numbers. The numbers were close to what I was getting using the HVAC4 program. At that time what I did not understand was how to size a heat pump to those numbers. The manual j said I needed a three ton system for cooling but five ton for heating. As I learned from members of this site (and from re reading the manual from the program) you should match the cooling ton and use heat strips to make up any additional heat requirements. A couple companies wanted to sell me a five ton two speed heat pump. What I was told by the people doing the bid is during the summer the unit would run in slow speed for cooling needs and come winter it would run in the second speed if needed for the extra heating ability. After looking at the bids and talking with a few other people I think the companies that gave me quotes for five ton systems event way over board with what they offered. 5 ton 21 seer electronic air cleaners big dollar maintenance contracts shiny things with bells and whistles sort of stud. Needles to say I did not go with those companies. Thanks for your time.


Is there any reason why you wouldn't go with the company that you gave a verbal commitment too? Do you not trust them, hence this post?

[grizzzlle]

No. The reason for the post was to thank skyheating for the offer to possibly come bid for my heating job. I did not want to waste his time. I also wanted to explain further the reasoning for the original post. I do trust the company I have decided to go with I just have only had the chance to talk with the people over the phone. We are going to set a time up to go over the bid again in the near future. Since I have made a verbal commitment I don't think it would be right to continue getting bids.

Again thanks to everyone who has offered advice.

[seatonheating]

No. The reason for the post was to thank skyheating for the offer to possibly come bid for my heating job. I did not want to waste his time. I also wanted to explain further the reasoning for the original post. I do trust the company I have decided to go with I just have only had the chance to talk with the people over the phone. We are going to set a time up to go over the bid again in the near future. Since I have made a verbal commitment I don't think it would be right to continue getting bids.

Again thanks to everyone who has offered advice.



Sounds good. Let us know the final outcome.

Also, we would love to see some pics of the system.