Heh, Im glad ya didn't take offense, its just my night off and I've had a few (too many?) beers and I'm feeling a bit saucy. Anyways, yes you are correct. If your system is oversized then it will not run long enough too pull the relative humidity down to an acceptable level. 72 degrees with a high RH could be uncomfortable. Just keep in mind if your new system is smaller, then it will generally run longer, and this is a good thing.
Originally Posted by bostonguy
No offense taken, I laughed when I read it. Hope you are enjoying your time off because you guys work hard and deserve your time when you can get it. I understand that a smaller system will run longer and is better. That's why I'm trying to make sure I make the right decision by reading and posting here.
Originally Posted by JohnnyValvecore
a blood thinner prescription could help tremendously
When its 20°F outside. I'll be outside working in a Uniform shirt, and a Tee shirt.
I keep a jacket in the truck in case it gets cold out.
In the summer, my place is 72°F, and 48% RH.
I like it cold. I don't think blood thinner would help me.
Yes indoor design temp can effect the load calc.
One may be using a higher infiltration rate then the other.
They may be using different load programs. Or different versions of Manual J, one may be using version 7, the other ver 8.
Ask them to put in writing, what temp it will maintain, and what %RH it is sized to maintain while running.
I agree with you Beenthere. When we are home it is normally on 72*. If it is decently warm outside I can easily keep it in the high 40's%RH. I was kind of misled by my contractor and this site as far as lowering the humidity to keep it comfortable. I was set on leaving it 75*. Now that I have had the system for a little bit, I leave it at 75* when not at home and 72* when I am there. Lower humidity helps, but I still like it cold. Maybe its a northern US thing? (I am in Northern, NY). During the winter anything above 68* starts to feel too warm to me.
I can give you the reverse experience and live in a climate very similar to yours.
I have a 2 ton York HP that is undersized. My manual j says I may need 2.5 tons, but a contractor I like and will probably use when this unit goes tango uniform says I need 3 tons.
On hot days it struggles to reach 77 degrees and so runs a lot. Consequently my RH gets down to 38% - 40%, or so says my Carrier Performance Series tstat.
I really, really like beenthere's suggestion of saying to put in writing what min temp and min RH they will guarantee.
I've had my place at 75° 44%RH, it still didn't feel as good as 72° 48%RH.
Comfort is a perceived thing. So many of the people here(including myself), are telling you at what temps and conditions, they perceive their comfort at.
I will ask about this, thanks for the suggestion.
Originally Posted by beenthere
I have a couple of questions if those that have contributed to my thread happen to see this. The contractor that I am seriously considering gave me the following info for things that were suggested earlier in this thread.
1. For design temperatures he said that he used outdoor temp of 95 degrees, indoor temp of 70 degrees and RH of 50%. Sounds reasonable to me, any thoughts or comments.
2. When I asked what values he used for wall insulation in the load calc he said in order to determine wall insulation he would have to poke a hole in the wall to see what is there. My house was built in 1969 and he said that houses built back then used little in the way of wall insulation so he said that he assumed worse case and used zero for wall insulation value. I thought that I had read somewhere that you can take the wall temperatures of an exterior wall and an interior wall and the temp difference would give an idea of insulation in the wall. Am I totally misunderstanding this? The contractor does seem knowledgeable so if he is usung a zero value for wall insulation should I be concerned?
I would be wondering.
He can pull a wall plate and check for insultaion.
I don't think your design temp in the summer is anywhere near 95.
Is 70* the temp you want to maintain? If it's 72* thats a Hank R. do not do.
I would cut a hole in my sheetrock and check R values before I would assume no insulation in my calcs.
What does Manual J use for your area? don't add degrees to YOUR design temp!
Go here and read Proctor info,http://www.proctoreng.com/articles/better.html
You have no idea how I wish I could find a contractor like you or any of the professional contributors to this forum.
Originally Posted by beenthere
Do you know what the Manual J design temp should be for the Boston area?
I'll also suggest that a wall plate be pulled and see what the response is.