HVAC duct code clarification - potential problem???
maxjackjoe
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maxjackjoe
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Please help: New HVAC and Duct problem
Comments (6)Thanks very much for your reply. The upstairs is 1100 sq ft. The main level is the same, as is the basement. The upstairs furnace is 50 BTU. The heating is natural gas. There is ductwork in the basement that supplies the main floor. The basement is unfinished currently. That may change. There are six vents upstairs with one return in the hall area. The return is 12x24. There are eight vents downstairs with one return in the hall area. The return is 12x24. I was told that the unit upstairs had a leak/crack in the compressor that could possibly leak carbon monoxide. There are marks on the outside of the unit that looks like burn marks. The heating unit performed fine the last time we used it before we found out about the burn marks. It is about 25 years old and about 8 SEER. The cooling unit seems to run almost all of the time in the summer. The downstairs unit also performs ok but needs a serious duct cleaning due to water from a pipe bursting in the kitchen getting into some of the ducts. We haven't used it in quite a while. The house has humidity problems sometimes (window condensation and my indoor hygrometer can get near 80% in the summer but is around 50% in the winter) and we would like a system that can take care of that and be more efficient. The upstairs unit seems to run all of the time in the summer. The stat is usually set around 75. I was told that 16 SEER two-stage would fit the bill. Other ac companies told me I needed nothing more than the typical 13 SEER. Some family members have asthma and I also want something that will help with that. How can I tell if my ductwork really needs to be enlarged? Thanks much for your input...See MoreProblems with HVAC in 1958 Cape Cod
Comments (26)"Generally, I am being told that my oil furnace is probably at the end of its life, being at least approx. 25 years old and should consider replacing now. The 2nd contractor that wants to replace existing with 4 ton furnace, states that the current one is not large enough to handle the size of the house. The rest, so far, want to add a separate system for upstairs." ----------- When the cooling A-Coil is set directly on top of the furnace the huge oil furnace heat/exchanger causes a lot of restricted back-pressure leading to a big drop in static pressure which reduces the velocity of airflow. That along with possibly improper duct design & return air filter areas would greatly reduce airflow. I am betting a 60K would heat your hone in that climate. Do your own whole house load-calc: http://www.loadcalc.net/ Or/and, do the floors separate. Print the instructions & follow them; including clicking on thr SIZING LINK when load-calc is satisfactory completed......See MoreIs your HVAC ducting in your unconditioned attic?
Comments (29)"One of the worst things that you could do in a house is install leaky ductwork in a vented attic." - Joe Lstiburek Vented crawlspaces can be even worse with humidity and soil gas issues. Worst case: In the OP's case which is "unfortunately typical" you get this: With that improvement, according to Lstiburek, you can still expect 30% higher heating and cooling costs compared to best example: Notice insulation at attic floor, not roofline. Taken from Joe's BSC resource: Are you doing something stupid? Many designs call for insulation at roofline, just make sure it meets minimum code prescriptions. The biggest problem with roofline sprayfoam is the allowance of ridiculously lower than code R-value minimums. The home as a system is big and complex. It's easy to break out any one component and argue that it's not a big deal to compromise on efficiency. The more one applies that philosophy, the more performance will suffer. It's not just energy use, indoor air quality and uncontrolled moisture movement are also influenced by these decisions. Not accusing anyone but HVAC contractors are notorious for selling oversize systems that increase profits with bigger equipment markups. I can also imagine contractors used to installing attic ductwork might frown on the better practice of conditioned space ductwork as it may create more headaches coordinating with construction teams not used to doing it. Slabs, increased window area and typical construction are not good excuses to continue poor building practices. I'm all for balance but significant ductwork in vented attics or crawlspaces is tough to justify for new construction....See MoreSingle HVAC zoned or two HVACs without zoned system
Comments (27)The biggest problem with HVAC zone systems is knowing when to choose it as a solution and when not to. Some HVAC companies it's about "sell, sell, sell" whether or not it works... there's more money in "sell, sell, sell" --- when it's only about money? So does the comment above mean I do it for free? No. If you think that you are reading things that aren't there. New construction? best to choose separate systems 9 times out of 10. In order for a zone system to work, you have to know what you are doing. Most HVAC companies staff (the techs they send you) are 20-30 year olds. How much practical experience could they possible have? It's best for HVAC zone systems to be an elegant solution. A HVAC zone system is a tool in the tool bag. Not all homes are suitable for zone systems. Some homes there is no other way, and in some cases complications to those problems will make an HVAC zone system design possibly more prone to problems. You have a problem now, do you want more problems. These decisions among others are decided "in person" --- so considering that becareful what information you decide upon from the internet. Just because it's here doesn't necessarily mean it's true. That said: Depending on equipment level chosen, how many different floors you have in your structure, how much room you have available... will all be factors that make you decide one way or another. From there it's in your best interest to pick a contractor that is skilled: especially when it comes to HVAC zone systems. (there's a lot of garbage out there.) (click to enlarge if necessary) I service the Katy, Texas area....See Moresktn77a
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