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You've received good info. I guarantee what happened, is the builder gave the energy calcs to his HVAC guy, and the HVAC guy said "here's your quote for 2 systems." The builder only assumed and priced one system. By code, though, one system isn't going to cut it after the energy code changes. So he's coming to you for more money. You don't want a zoned single system; you want two systems, one for each floor. Is that what you mean when you say "zones"?
Anything less than a system per floor is a gamble on your part, with risks. Accept that before entertaining any work arounds.
Just for clarification, are you saying it is better for me to go for a zone for each floor? The builder is suggesting one zone for 2nd floor and another zone for basement and 1st floor combined.
I, among others, view zoned ductwork as an expensive last resort for retrofitting existing systems that have no opportunity to split/divide. To properly retrofit a zoning system, the ductwork almost always requires some major changes that may or may not be accomplished w/o structural work. Zoned ductwork isn't configured the same as single zone ductwork. You may not have the opportunity to correct a system's shortcomings down the road.You won't likely be satisfied with a single zone solution in a multi story structure.
If I understand it right, if I choose only 1 zone for the whole house, I may have to live with it if it is not right.
You'll likely have stratification even if you run the blower continuously to stir the air where as with multiple smaller systems, each floor will have it's own return if the plan is to use a central return...a BIG plus. Smaller independent systems will naturally have smaller ductwork which helps when allocating space for soffits or shafts.
Again I see that you are suggesting I not go with one zone for the whole house.
As far as expenses, zoning reduces efficiency..it's only benefit may be comfort. Add the inefficiency into the lifecycle costs and you'll find that your energy provider has been financing your poor decision thru additional energy use rather than to complete the project properly and add the cost to your mortgage. Based on that, I'd disagree with the costco kiosk person. Energy costs are expected to rise 3% annually on average. HVAC should be 8-10% of the total cost to build a multi story structure and ongoing maintenance cost for a home, not just the hvac system, are in the 2-4% range annually.
I am surprised by your statement (marked in red). I thought zoning increases the efficiency simply because we will have the option to turn off heating or cooling in parts of the house that are not being used.
What temperature do you intend to maintain during the cooling season? Equipment capacity is rated at an indoor temp of 80.
We intend to keep a temperature between 70 and 72.
What duct leakage rate will your hvac contractor be providing you with and will it be tested and documented by an independent 3rd party? Duct leakage, among other things, heavily impacts comfort, capacity, and energy use.
I took your advice and asked the builder for Manual J & D calculations. He has written to the contractor to provide them.
When I get the calculations from the builder I don't know what to do as I have no knowledge in HVAC systems. Would you mind if I ask for your help in studying the calculations and give me your opinion as to what system I should get? I really appreciate your help so for and I hope you will indulge me further.
Don't be rushed into a poor decision, You're the one writing the checks and you're the one that has to live with the outcome.
Be extremely inflexible! Nothing happens, nothing, until the documented Manual J & D calculations are in your possession for review. Everything is hinged on their correctness.
The builder is now complaining that this will delay the completion of the house. I may have to stick to my guns and make sure I get the system right before proceeding.
Just for clarification, are you saying it is better for me to go for a zone for each floor? The builder is suggesting one zone for 2nd floor and another zone for basement and 1st floor combined.
Zones are areas with distinct heat loads that exhibit "adequate exposure diversity" meaning areas with dissimilar temps...north vs south, upstairs vs downstairs, living vs sleeping, etc. How you manage them is important. Separate furnaces & A/C for each zone is best, "zoned ductwork" of one furnace & A/C to serve 2 zones is troublesome. Don't confuse the two.
Combining the 1st floor and the basement as 2 zones on 1 system could be feasable if done correctly.
If I understand it right, if I choose only 1 zone for the whole house, I may have to live with it if it is not right.
Yup.
You'll likely have stratification even if you run the blower continuously to stir the air where as with multiple smaller systems, each floor will have it's own return if the plan is to use a central return...a BIG plus. Smaller independent systems will naturally have smaller ductwork which helps when allocating space for soffits or shafts.
Again I see that you are suggesting I not go with one zone for the whole house.
Yup
As far as expenses, zoning reduces efficiency..it's only benefit may be comfort.I am surprised by your statement (marked in red). I thought zoning increases the efficiency simply because we will have the option to turn off heating or cooling in parts of the house that are not being used.
It simply doesn't work out that way for "zoned ductwork". There are published studies that dispute the savings claims made by the makers of duct zoning controls. My state, california, has removed energy credits from zoning because they don't offer any savings and prohibits the use of bypass dampers because they're so wasteful. Carriers infinity system does a pretty good job at not wasting energy but on average, efficiency declines 10-20% if the duct zoning isn't done the way my previous post stated. Keep in mind that you'll never want an unoccupied area to deviate more than 4-5 degrees or the recovery will be too long.
We intend to keep a temperature between 70 and 72.
Equipment capacity is reduced 30% at 70 degrees....2 tons of equipment is capable of 1.4 tons worth of work when you drop the setpoint from 80 to 70. Or in other words, you'll need 2.5 tons of cooling to meet a 2 ton load at that indoor temp. The equipment needs to be properly derated. You'd better make that, and many other things, clear to the contractor prior to allowing work to begin. Indoor temps are one of the many parameters of a proper Manual J calculation. ACCA Manual S derates equipment and is a line item of the boiler plate stuff your architect wrote.
What duct leakage rate will your hvac contractor be providing you with and will it be tested and documented by an independent 3rd party? Duct leakage, among other things, heavily impacts comfort, capacity, and energy use. This issue needs to be addressed. It's a line item from your boiler plate image.
When I get the calculations from the builder I don't know what to do as I have no knowledge in HVAC systems. Would you mind if I ask for your help in studying the calculations and give me your opinion as to what system I should get? I really appreciate your help so for and I hope you will indulge me further.
No problem. If your builder gets snarky or impatient because you have an internet source whispering tips in your ear, tell him/her (with a scowl) that's because his/her hvac contractor dropped the ball. Everything I've mentioned is stuff that should have already been discussed and settled...a long time ago.
Location: Central Atlantic Region, though consults worldwide
266 posts, read 450,103 times
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Quote:
Originally Posted by ymd
Our 2450 sqft house in Maryland is being built. The builder was giving me one zone HVAC. His contractor has suggested that a 2 zone HVAC would be much better for our house. Our house is a colonial with a basement.
The builder gave an initial estimate of an increase of $3500 to make the HVAC 2 zone. Now he is saying the estimate was assuming a 2 Ton system for the 2nd floor but the contractor now says the 2nd floor needs 2.5 Ton system and the price difference would increase to $5000.
They are beginning work on Monday and I need to give my decision ASAP. I have no idea about HVAC systems. Just did a brief research online. I am unable to decide if I need a 2 zone HVAC (or possibly multi zone with thermostats in each room). Could someone help me decide if I need a 2 zone HVAC (one zone for basement and 1st floor and 2nd zone for 2nd floor)? Also, is the price quoted by the builder reasonable? What questions should I ask the builder to make sure I am getting my money's worth.
I am in Maryland and would have enjoyed helping with this problem however it appears time is tight. The reality of multizone is that the total home tonage my be reduced. So, while the first level might have beew a 1.5 or 2 ton unit and the 2nd level 2.5 tha total may be 4-4.5 tons. The approved formulas are such that the aggregate may be reduced by a certain percentage, often by perhaps 35%. More system cost in one respect, much less in another.
For instance the cost of a 2 vs a 2.5 ton unit is not that much machine wise. However you will need to trnsition cost savings of one machine to cover the zone controls. Admittedly, there are many things to consider technically prior to a zoned system vs a separate machine zoned system. I am proven partial to the dampered systems however basic HVAC contraactors simply are not familiar with them. Ducting design, for instance, requires significant knowledge, as wel with the controls.
I might suggest you stick to your guns because it is your that will forever paying the energy bills. Zoning affords an economy of operation unlike separate systems.
I have done homes up to 14 zones without issue. In fact, I have an 8ksf home in Georgetown that operated with a 112K btu gas furnace and a 5 ton A/c system. Ramping the cost up in such situations is gouging. I have made it my mission to save money -- not cause customers to put more on the table.
Hope this helps.
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