ReplyLook for member "Paul42". He has a 4200 sq ft house, with a 2 ton A/C. he lives in Texas. So a 60,000 BTU furnace may be the right choice for your house.
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It appears that residential HVAC is mostly a black art (i.e.: a process that is mysterious and difficult to master or describe.)
> Pretty much everyone seems to agree that a 60,000 btu whole house heat loss (bumped up, at my request, to a single 100,000 btu variable speed propane fired furnace) is ridiculously low, despite a Manual J, S and D design from an outfit that is experienced and credible.
> Some of you suggest that the contractor and designer should be the same firm. I like that idea, too, but how does that solve my problem- I can't find a contractor that designs systems based on science. They design them based on rules of thumb and experience (and, by the way, they have many satisfied clients). And of the designers that I've engaged with, one did the Manual J, S and D that I posted and the other had never heard of Manual J (a California licensed PE, by the way).
> Some of you suggest that this house needs a/c. I've attached a document that summarizes the temperature data from 1961 from the closest station to us (on the Pacific Coast, about 20 miles due North). We didn't think we needed a/c, based on this data (which mirrors our experience at the site). Are we reading this wrong- does anyone still think we need a/c?
> Regarding zoning, we had planned on the system mentioned by GA-HVAC-TECH. It's called My Temp, by Home Comfort Zones (Removed link ). It is essentially a room-by-room zoning system. HOWEVER, this zoning system does not eliminate the need to properly size a whole house heat source and distribution system.
So I ask again- "Can anyone tell me why I shouldn't just go with the bigger system (250,000- 300,000 btu) and play it safe? The additional cost is peanuts compared to the size of the project, we don't have any LEEDS, Energy Star, or regulatory compliance requirements, and the hassle that this is causing doesn't seem to be worth the effort to try and do it the 'technically correct' way."
Last edited by beenthere; 03-25-2012 at 12:10 PM. Reason: removed link
God Speed, Jim. We'll miss you - 2-26-23
Look for member "Paul42". He has a 4200 sq ft house, with a 2 ton A/C. he lives in Texas. So a 60,000 BTU furnace may be the right choice for your house.
Professional Member*
You have had a few options (including my own with the boiler, radiant floor and fancoil) so there should be lots of options available to you.Originally Posted by confusedHVAC
Even in Toronto, where the design temp is -6f..... 300,000btu would do a 10-12,000ft2 house. It is a complete waste of your time and money to install something like that. It would have to be done with 2-3 furnaces anyway.
Professional Member*
The reason I suggest cooling, is that a home this big is likely to not only hold the few residents. Tight homes are especially prone to 'party heat', where you have a get together at the house, and everyone ends up sweating. As you mentioned, the system would be a mere fraction of the home cost, so why NOT be prepared for it?
As for oversizing the heating, this is partly why I (and a few others in this thread) recommended hydronic. No-one ever worries about oversizing their water heater, because having too much hot water is never a problem. Hydronic also eliminates the potential for air balance and distribution problems in a home this large.
Speaking of air balance, what does the home have for forced ventilation (meaning outside air refresh/exhaust)?
Professional Member*
Please do not take this personally, it is not meant that way; however:
Science and what works are sometimes two different things. I realize that sounds like a contradictory statement... however when lots of contractors say the same thing... one should listen to them.
The issue is the size of the home and the ductwork required to distribute the air... just not a fit which will work.
And if it were me, I would take the post above which explains 'party heat' seriously. I would HATE to be the host of a 50 or 75 person party... and everyone is hot and sweaty because the $M+ house does not have AC...
What would YOU do if you attended that party at your friend's home? Yeah, we all know what we would think and what we would do... <grin>
The world is not going to come to an end if you install 3 or 4 systems in that house which are low capacity and run a small amount.
Good luck with your project.
GA-HVAC-Tech
Your comfort, Your way, Everyday!
GA's basic rules of home heating and AC upgrades:
*Installation is more important than the brand of equipment
*The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
*The value of comfort, over the long term; leave economic choices behind!
Choose your contractor wisely!
Professional Member*
You can, but you won't need all of it!
I've noticed your Heat load calc and the CFM requirements that was done; I say you need the right amount of airflow capacity from appropriate equipment/s and yet not oversizing the equipment.
I think natural gas is more economical than electric according to what I hear from util companies there.
Your system/s can either be simplistic or complicated depending your requirements by you or city/state codes. Have you looked into possible codes that are required like fresh-air! This alone can mean an end to the type of system you might have to need or require!
Your region is unlike my region. I know how to design and what type of system to recommend for cases like yours (your house size) if you were in my area. But I'm very limited to helping in designing a system like yours when you have a much milder weather than where I'm from.
I say again, keep looking/searching. I remember hearing and reading about some good HVAC companies in the Sacramento area, i think!
Professional Member*
ask your PE about micro climates.
Unless you're building near the airport( your report's weather data) which I doubt, your data will be more like Morgan hill or Alamaden~90.
Plus, some day the house will go on the market, unlikely any qualified buyer for a large home will have tract home expectations.
Professional Member
Cool Air
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Professional Member*
Sorry if this has already been addressed, but as a licensed contractor in Texas, state law states the YOU as the license holder CANNOT sub contract the design of the system to another company who does not hold that license.
So, how many energy auditors are licensed HVAC contractors?
Philippians 4:13I can do all things in him that strengthen me.Apostle Paul inspired by GOD.
Professional Member*
The real reason many units get oversized is because there is more profit in a bigger box.
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Last edited by beenthere; 08-22-2013 at 03:41 PM. Reason: Non Pro * member
God Speed, Jim. We'll miss you - 2-26-23
Barbie B., this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here.
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