I purchased the HVAC calc program a couple of days ago and have been enjoying using it to try and figure out ways to reduce the heat loss from my home in RI.  I have been getting some results that surprised me and wanted to find out what others thought.

I currently have R-30 insulation in my attic and no insulation in the floors over a full unfinished basement.  My initial results were 63,000 BTUH for heat loss and about 30,000 for heat gain.  I was thinking of adding additional insulation to my attic to bring it up to R-49.  The program only allows R-44, so when I switched to that, it really didn't help that much.  Maybe a couple thousand BTUH's less with the R-44.  When I tried putting R-19 insulation in all the floors however, it made a huge difference.  The load went from 63K BTUH down to about 46,000 BTUH.   Does this seem right?  The reason I question this is that I had an energy audit of the house a while back and the guy suggested adding more attic insulation, but didn't really mention isulating the floors.

Also what about the disparity between heat loss and heat gain?  Everything I have read here says I should size the unit for cooling and not heating.  The local installers I have spoken with seem to suggest the opposite.  If I size for the heating season it would seem the unit would be too big for properly cooling in the summer(basically 3-4 months around here).  One installer said that with a 2 stage unit it would be O.K. as it would mostly run in the first stage.

I have a few more HVAC calc questions but I won't go on forever.  Thanks

As the R Values increase, the amount of savings you will see will decrease. So if you were to go from a R-19 value to a R-30, the efficency gained would be much higher than say a R-30 to R-49, as the R value increases the amount of efficency gained decreases. Is R-49 better than R-44? Absolutely, but energy savings may not be worth the insulation cost or the payback period for energy saved vs. install costs would be much longer than say a R-19 to R-30 improvement. Thus I don't think bringing up your R Value to 49 is really going to save you all that much in the way of heating bills. 
 
I've read that insulating my unfinished basement make the house save on the heating bill in the winter, but do nothing for me in the summer. I was pretty much set to get ahead with the project, but other people I spoke to told me that insulating the basement would provided miminal savings, it's more cost effective to make sure the areas boarding the outside are well insulated, including insulating the basement walls, 4 feet down from the ceiling. 
 
  

Possibly. For that kind of difference, I would expect that the software has the basement as unheated. If the basement were heated, then the addition of insulation between 2 heated areas makes little sense, and should not have a big affect on your heating loss.

Hi jc

The software does have the basement as unheated which is the actual case in the house. It would seem to me then that it would be well worth the expense to insulate the ceiling in the basement as I have no plans to use it. If I do use it in the future it would only be a small section of it.

Actually, you'd be better off insulating the walls of the basement, and not heating it. It will do a better job for the duct to have the basement insulated instead of the floor. Duct insulation is seldom as good as just keeping it in semi-conditioned space.

One thing I wonder about with your HVAC calc program is the tightness you're giving the structure. Many testing companies that use blower doors typically find the following air change rates:
-older homes with fiberglass batts, .45-.65 (the lower the number, the better)
-new homes with fiberglass batts, .35-.45
-older homes with cellulose, .2-.3
-new homes with blown in fiberglass, .25-.3
-new homes with cellulose, .2
-homes with a mixture of foam and cellulose or foam and fiberglass, .1-.2
-homes built with foam, Icynene, urethane, ICFs, SIPs, etc., .05-.1

The number denotes a percentage of natural air change rates of the home, even with those insulations. So, an air change rate (ACH) of .2 means that during each hour, 20% of the house's air volume naturally changes with the outside air, due to leaks to the home.

Anyway, after rambling on about this...my point is that the air change rate you have in your home will greatly affect your load. It's not just the R-value you need to know. You need to know how LEAKY the home is, too.

Hi Tuffluck

So you think it would be better to insulate the walls of the basement and not the ceiling? I was thinking that by insulating the ceiling of the basement(or the floor of the first floor) I could keep the heat within our living area. It doesn't get that cold in the basement in the winter now, but I also have an oil fired boiler running. That won't be the case when I make the switch to geo. The basement is fully underground except for the top 1 1/2 ft. The foungation is 12" thick poured concrete. Will insulating the walls make that big a difference? I was wondering if it might make sense to upsize the geo unit and heat the basement to some extent with it. It is 2500 Sq. ft. in an "L" shape and completely open. I really have no plans to use the space for anything so I'm not sure this makes sense.

As far as the tightness of the house, I used the middle or average value in the software. The house is 20 years old and does have what appears to be a Tyvek vapor barrier and it is 2x6 framing with R-19 insulation in the walls. I haven't had the house tested with the blower door, but I have been on a crusade to seal it up as much as possible with a new entry door, weatherstripping, caulking, localized insulation, sealing all the holes I could find in the basement and attic with Great Stuff expanding foam, etc. It might be worth it to do the blower door test and see if there are areas I missed. Thanks for your input and comments.

Sure the insulating the floor would save energy too, but the walls is where the cold outside air is where the problem lies. It's far more cost effective to concentrate on the walls, Use wallboard insulation.


I just recently had my house tested with a blower and you would be suprised where air is leaking into the house when they run the test. I wish I had one, I could leave it run to identify every crack in the house where air is coming in.

I have the calc software you're referring to and find it to be user friendly and reliable. It's few short comings are not likely to skew a load by a 1/2 ton which is fine for residential geo design.
I load every house as having a finished basement. As Tuffluck points out, you either have btu's to heat the basement or lose btu's where duct work travels through unconditioned space and you never know when someone may decide to utilize the space so why not allow for it?
In your area and mine you would definately size with an eye toward heating. I agree that a 2 stage unit would help with humidity issues in the summer but there are other ways to do that as well.
You'll also want some help in the duct design which will be critical. Your software's duct sizing recommendations are accurate, but expensive. For example two dampered 6" runs, in my area, are cheaper than one 7" branch.
Good Luck,
Joe

Hi Joe

Thanks for the good advice. With the basement added in to my calculations as heated, I get a heat loss of 70,000 BTUH and a total heat gain of just under 32,500 BTUH. That would mean roughly a 6 ton system, yes? With just the first (and only) floor insulated with R-19 insulation and just the first floor heated I get a heat loss of 46,000 BTUH and a total heat gain of 29,500 BTUH. That would seem to be a 4 ton system. I guess my question is this. How much heat will be lost by having the duct work in a full basement(it is not a walk out)that is not heated? And trying to keep cost down as much as possible, is it really worth the extra thousands of dollars to increase the system size by two tons considering I have no intention to utilze the basement as there is more than enough room for us upstairs. If I or someone else ever wanted to use part of the basement I would probably use a pellet or wood stove. I am not trying to be argumentative, I just want to try and determine the best, most cost effective way to use a geo system to heat my house.

Wow, a heat loss of 70,000 BTUh is a huge heat loss. What is the infiltration rate you have it set at? If you really have a 70K BTUh load, you're really burning through some $$$$ to heat it, right?

I just got done drawing up a plan on Wrightsoft that's a main with a basement, total square footage is about 5000 sf. This includes a garage on the walkout basement floor heated to 50 deg. in the winter. The outdoor design temp is -10. The infiltration rate is .30 for his setup (cellulose walls and ceiling, but has 2 fireplaces with dampers). The total heat loss is 69,984 BTUh, and the gain is 32,001 BTUh.

The heating load on this one is so high because of radiant tubing loss (about 9000 BTUh), and because he's not insulating the garage very well, but wants it to be heated via radiant floor.

I guess what I'm getting at...I think your 70K Btuh calc is a little high. It's hard to believe that your loss is so high with just a basement and main level.

Also, with a 70K btuh load, you're looking more like 7 or 8 tons to cover that load. Remember, you don't get a full 12,000 BTUh output at design temps. Hope this post makes sense...

I'm sorry, we're a little to general on information with specific load calcs.
How many square feet is the house?
The Basement?
How deep are the walls?
Is it a walk-out?
Sounds about right the 10% difference between duct in unconditioned basement or conditioning the space, but this is where we lean on the operation cost software. The difference between a 4 and 6 ton unit might be $7k in installation cost (between additional ground loops, duct and electric requirements) while using an aux. electric coil may only add $100/yr in operating cost.
Your heat gain load suggests a 4 or 5 ton unit to me with a 10ishK aux. heater.
This is where a local installer with local experience is important.
The heat load is only 1/2 the info. Geo design software is the other 1/2.
I loaded out a home the other day where the projected operating cost difference between a 3 and 4 ton system (without hot water generator) was $12/yr. Additional installation cost for the 4 ton was about 2K. Not a great return on investment.
Peak load at 70k may be 2 days a year while 98% of the year comes in at 45MBH.
Consult and trust local installers. Let them load the home and use your calcs to verify their findings.
Joe

Hi Guys

Thanks again for your advice. To answer a few of your questions. The house is 2700 Sq. Ft. with a 2700 Sq. ft. full basement. It is not a walk-out. The walls are 12" thick poured concrete foundation. About 5 1/2 feet are underground and 1 1/2 above. The attic has R-30 insulation, the walls R-19, and the basement has no insulation. I am by no means an expert with the HVAC calc, so I could well be off. I am going to be getting a load analysis hopefully next week from what I think is a reputable company with quite a bit of experience. I hope you are right and it turns out to be lower. I am just trying to be as informed as I can to understand all the aspects of these systems and be able to ask intelligent questions so I am as comfortable as possible before laying out what to me is a great deal of money.

Sounds like a ranch with a 7' basement. The low cieling ht may be why you indicated no plans to finish it. Insulating the duct work may not be a horrible idea. Your installer is going to have to make some recommendations here. I recently had a simillarly sized house that we used a 2 stage 5 ton in. A case wase made for the 6 ton, but the additional duct required made the larger resistance heater more attractive.