I am building a new 2080 sq. ft. ranch with a full basement (additional 2000 sq. ft. that will eventually be finished) and am wondering what size of unit I need. The new home will be in Ann Arbor, MI (Southern part of MI). The house has nothing "extra" as far as insulation, but will meet the new code requirements. It has 2x6 inch walls with cellulose insulation (R21) and blown in insulation in the attic (R49 I think). The windows are standard vinyl Pella windows. I haven't seen the load calculations, but one company quoted a ClimateMaster 3.5 ton and one quoted a Comfort Aire 5 ton. The house is on 10 acres, so I am going with horizontal trenches. I know I don't have a lot of details here, but it seems a big difference between the size of the system in the quotes. Could two companies really be this far off? What seems more reasonable? Thanks for any insight.
Seconding what @dgbair said, you really need to ask for the load calculations. One idea is that contractor #2 (5 ton) may have been trying to "play it safe" and give you a larger system, or may be trying to take advantage of improved equipment efficiency at part load. I don't personally agree with either strategy, but there are others that do.
Yes two companies can be that far off. There are different strategies in attacking load. IMHO folks who load heavy actually stunt your ROI. The other thing I've noticed lately in new construction is that the consumer often has the builder do the shopping for them and there is much to talk about with the contractor you hire. Our mantra around here is dealer dealer dealer. Buy from the right person and the size, loops and everything else you might worry about will be taken care of. If you have the load calcs. we could better advise you. If you want a third opinion on your project, you are within our AO. j
Thanks for the info. The builder is doing the shopping, but I'm asking to speak with the contractors directly. I have a meeting with one this evening....the one who quoted the 5 ton system. I hope to get the load calcs and will reply with the info that I can get. The builder is pushing this guy a bit as he is doing the other plumbing in the house. I just want to make sure the system is sized correctly and installed correctly.
The contractor came back with the manual j calcs... 61,315 btu heat loss 25,152 btu heat gain What size system is needed?
If the numbers are correct, there is nothing wrong with a 5 ton. A 3.5 ton might be a little light for my taste, but Michigan charges less for electricity, so it might be thesible as well.
Doc it's quite a few less peak load hours around Ann Arbor making the 5 ton overkill. It actually has a higher operating cost in many scenarios than the 4 ton. The 3.5 ton could get the balance point in the mid-teens but will cost about $100/year more to run than the 4 ton and $50/year more than a 5 ton (if you have DTE). Mid-teens is our target balance point around here when designing off of manual J since actual balance point is often 10F less than manual J and op cost models predict. So your builder is shopping. Builder's shop by price so the 3.5 ton will work and it saves the installer a few bucks so he can bid lower. A similar situation was put before me recently where the 3.5 ton cost $69/year more to run (~55kbtu load) but saved a few hundred dollars so I could bid in lower. I am not invited to have a discussion with that client (which frankly means I'm mailing it in). One of the pools of dis-satisfied geo owners we see here routinely are the ones that let their builder "handle it". Often their regular heating guy gets to take a whack at geo (hey ya'll hold my beer I got this), things such as choosing a 5 ton over a 4 which costs more to run are signs of inexperience (ask them to show you some of their systems at work through monitoring equipment, they likely don't know they cost their clients more money in both first cost and operating cost). The builder doesn't shop his buddy as hard as other contractors he's not used to working with so it may actually cost you more mark-up as well as more first cost from larger system. The other bid you get from the builder is the lowest bid. I know a 3.5 ton will work and it lets me offer the lowest bid. The right size for that load is a 4 ton. However that load is ridiculous for a 2000 SF walkout and possibly generated by gigo. It's quite possible with aggressive insulation strategies (or an honest load calculation) a 3 ton is the right fit for your home (meaning the guy with the 3.5 ton may be oversizing, but at least he's closer to the real size requirement I'd be curious to see his load calcs). You need advice from a real pro. If you don't care to use us find some one else for a third opinion.
I am never the lowest bidder, but all of my designs keep my customers happy and comfortable. I would let Joe have a look. Mark
Thanks Mark, checks on the way . I have prints and will do a load and we'll see what size makes the most sense.
Based on my calculations the 3.5 ton would be satisfactory with the 4 ton about $60/yr less expensive to operate. The quality of construction (tightness) is necessarily above average, but not automatically tight. That's the question. In no case would I recommend a 5 ton for this project as it simply would add more first cost and operating cost both.
Joe: I will wink at the mail box for a day or two. I am finding that the new "tight" closed cell stuff filled with anything is off the charts on infiltration numbers. The re-build/add on we did in Avon, OH ran through the polar vortex with half of the BTUH manual J said we needed. Your designing for some aux heat should shine in that type of build. I trust your math. Steph gets the drywall screws out of her hip Wednesday, and we may be headed to GA in July. Have him call me if you need a reference. LOL. Mark
