I am having a hard time finding any hvac companies in this area (Nixa, MO) who are familiar with ICF building, or tight houses in general. I am about to start on a 3200 sq ft walk out basement home. It will all be ICF with 2.5 foam. The roof will be sprayed with (most likely) 2 pound closed cell foam. My hvac installer is recommending a 3 ton heat pump for this set up. Does that sound to large? He said if we drop it down to a 2 ton unit the system wont be able to push enough cfm for that size house. Thoughts?

I think you need to do a detailed analysis of the home's heating needs, particularly if the local companies are not familiar with your chosen building method.

Don't let someone guess at what you need.

One common form is called a "Manual J Residential Load Analysis"

If they can do a Manual J properly, then ICF experience doesn't matter.

If you do end up with a 3 ton unit, I would recommend that it be a two stage unit to deal with with the humidity when temperatures are not at their peak.

A major consideration for cooling regardless of how much insulation you have in your walls and roof is the orientation of your home (do you have windows on the east and west side of your home?) and shading (porches, roof overhang, trees, etc.).

I you have the time and inclination you can model the energy use & peak heating loads with DOE2 or BeOpt (both freebie download tools from the US DOE), which will do a better job of factoring in the thermal mass aspects than a Manual-J. Three tons cooling might even be on the LOW side, if you have a lot of window area (particularly west-facing window area)- it depends on which direction the glass faces, shading factors, and the SGHC of the windows.

The 2lb foam in the roof is great for air-sealing, but is very expensive way to hit code-min on R value, and having a high-R roof (R50 or better) is also important for controlling peak cooling loads. Using 1-2" of 2lb foam to air seal then beefing up the R with a foot of cellulose is fairly cost-optimized. Avoid fiberglass in an attic/roof application- it's too air permeable to prevent loss of performance at the cold temperature extremes, and too translucent to infra-red to get the full rated performance under a hot roof deck.

If using a Manual-J type heat load calculation, be sure to use realistic 99% and 1% outside design temperatures- many an HVAC pro will have a tendency to put their thumb on the scale with de-rated R values or exaggerated design temps. Your 99% heating design temp should be about +10F, your 1% cooling design temp about 93F for fear of undersizing, but that fear is even less rational in a mass-wall house that has been air-sealed with foam. For design temps see:

http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/Outdoor_Design_Conditions_508.pdf

Posted By onesojourner on 20 Aug 2012 08:56 AM
I am having a hard time finding any hvac companies in this area (Nixa, MO) who are familiar with ICF building, or tight houses in general. I am about to start on a 3200 sq ft walk out basement home. It will all be ICF with 2.5 foam. The roof will be sprayed with (most likely) 2 pound closed cell foam. My hvac installer is recommending a 3 ton heat pump for this set up. Does that sound to large? He said if we drop it down to a 2 ton unit the system wont be able to push enough cfm for that size house. Thoughts?

Is this a 2-story or a ranch with a basement?

Posted By onesojourner on 20 Aug 2012 08:56 AM
I am having a hard time finding any hvac companies in this area (Nixa, MO) who are familiar with ICF building, or tight houses in general. I am about to start on a 3200 sq ft walk out basement home. It will all be ICF with 2.5 foam. The roof will be sprayed with (most likely) 2 pound closed cell foam. My hvac installer is recommending a 3 ton heat pump for this set up. Does that sound to large? He said if we drop it down to a 2 ton unit the system wont be able to push enough cfm for that size house. Thoughts?

Look for someone who uses Wrightsoft. That's the most used commercial software for HVAC sizing and contains info needed for ICF construction. If anyone says they don't need to use a program for HVAC sizing stay far away from them. My nephew HVAC contractor sized my system with it and we decided on a 3 ton Daikin heat pump. It does the job quite nicely and size is pretty much dead on.

What kind of heat pump are you thinking about using? If you haven't already, take a hard look at a mini split system such as Daikin or Mitsubishi. Lennox now offers one also. The big plus with the Daikin is it has a variable speed compressor that runs only as fast as needed to meet the heating or cooling load at the time. The Daikin also will put out heat down to 0° F. We have had below zero temps here occasionally and the heat pump has always put out the heat needed. Its output drops to about 27,000 to 30,000 Btuh at 0° F. My backup heat source is a pellet stove. There are no backup heat strips in the Daikin system.

My house is 2000 sq ft in SW Idaho, 11 inch ICF forms with R40 spray foam on the underside of the roof. The 3 ton unit is just right. Is 3200 sq ft the total for both floors, or each floor? If each floor I think a 3 ton HP may not be big enough. If both floors then 3 ton is probably plenty adequate. The advantage of the Daikin variable speed compressor is over and under sizing is not near as much an issue as it is with a single speed, or even two stage, compressors.

If you haven't already, peruse the Geothermal forum here at GBT for more info on your options.

As big a fan I am of ductless heat pumps (mini-split/multi-split), it's not clear that it will always be the right choice for standard R20-R22 sprawling ranch houses with code-min attic R and code-min windows. But it might be workable here.

It really depends on the room-by-room heat load, the floor plan layout of the house and the peak heating/cooling loads of the different zones. There are many decent-R homes that can work just fine with a multi-split, one head per floor, but also many that won't due to radically different cooling loads on different ends of the house, etc. Most mini-splits are pretty efficient in places with +10F heating design temps though, challenging ground source heat pumps on seasonal efficiency (at a fraction of the upfront cost.)

All of the high efficiency ductless systems use inverter-drive continuously variable-speed compressors these days, it's not just Daikin. Mitsubishi & Fujitsu together own the lions share of the US market for ductless (probably over 75%), but there are many good models from other vendors (Daikin, Sanyo, LG etc.) IIRC Many of the internal components of other vendors are standard Fujitsu parts. The "magic sauce" of the highest efficiency models is in the control-algorithms baked into their firmware.

Don't design or choose ANY system without the load calculations, but keep your options open. If your peak loads are well under 3 tons ductless could be a slam-dunk solution, or not, if you have a lot of high-load doored off rooms.

I had the same problem.  Finally I threw in the towel and asked my engineer/architect.  He told me to look at my Title 24 provisions which came with the plans.   It's this long behemoth of a mammoth of a document.   See link below.  Needless to say I procrastinated and haven't looked into it yet:)   Perhaps your state has something similar?

http://www.documents.dgs.ca.gov/bsc/Title_24/T24TrainingGuide.pdf

Take a look at Energywise Structures. They could really help you optimize your system to your specific situation. They are very familiar with ICF construction.

http://www.energywisestructures.com/?page_id=244

I recently used energywisestructures to size my plans. I was happy with their service. They break your specific plans/design down and give you a lot of details. They specialize in ICF, SIPS and similar structures.

I have about 8000sqft conditioned space in my design. They calculated out to a 9.5 ton system. I will round that to two 5 ton units.

Thomas

What does the fee schedule look like for Energywisestructures?

Are they expensive?

LBear,

The fee's start out at about $600 for the full audit. At Quad Lock we use them for ICF vs _____ comparisons. They can give you the monthly heating / cooling costs for a specific structure if built with ICF and also generate the costs if built out of wood, cmu, etc. It can really help a customer that is on the fence make up their mind to use a better building method. The have a custom program that is tailored to sizing systems for tight homes.

Posted By nd96 on 22 Aug 2012 05:20 AM
I recently used energywisestructures to size my plans. I was happy with their service. They break your specific plans/design down and give you a lot of details. They specialize in ICF, SIPS and similar structures.

I have about 8000sqft conditioned space in my design. They calculated out to a 9.5 ton system. I will round that to two 5 ton units.

Thomas

9.5 tons for 8000' that's 842'/ton, which is on the high side unless you have a lot of solar gain from windows late in the day.  For most larger homes the load per square foot is lower than for average homes, and in higher-performance average-sized houses w/decent performance windows using a rule of thumb of 1000'/ton cooling would be sufficient (or even oversized) almost anywhere in the lower 48.  A lot of west-facing glass can boost the peak cooling load substantially though.

Did they give you a room-by-room heat loss/gain calc, and tell you the 99% & 1% outside design temperatures used? 

Do you know what software package they used?

$600 is "in the range" for doing a careful load calculation- some HVAC contractors doing load calculation will charge for that analysis up front, but reduce the quote by that much if you contract the work with them.  Either way you should get the room-by room numbers, the whole house number, and the design temps used in the calculation as part of the analysis.

Posted By Dana1 on 22 Aug 2012 11:00 AM

9.5 tons for 8000' that's 842'/ton, which is on the high side unless you have a lot of solar gain from windows late in the day. 

Out here in Phoenix Arizona on a 2-story (3,800 sqft), they will install two 5-ton units. One for each level. That is common practice out here.

Mostly 2x4, R-13 fiberglass batts, cheap stick frame buildings out here. $300 - $600 a month summer electric bills are average for Phoenix homes.

I just finished building my home with ICF and couldn't be happier with the system I installed.  I do heating and air for a living, so the install wasn't bad.  What really stunned me was the numbers I came up with after running the house through "HVAC Calc".  The home is 4200 sq ft above ground w/ 1900 sq ft walkout basement.  That program was critical for proper equipment sizing.  I can't tell you how many guys I know that have done this for a living told me I'd be miserable if I only install a 2 ton unit for the second floor and a 2.5 ton for the first floor (ducts also feed basement to help dehumidify).  I can tell you, I am very happy with this setup and would not install anything bigger.  HVAC calc came up with a total of 41000 btus (just under 3.5 tons), I decided up increase the main floor unit to compensate for times we have family get-togethers (can be upwards of 35 bodies in the house).  To compensate, I installed a 2 speed unit for this floor.

As for heating, again, the numbers are extremely low.  I opted for 2 speed furnaces each at 60K btu- low fire is roughly half to avoid short-cycling them.

Bottom line is don't let anyone talk you in to sizing the equipment based on "rule of thumb", they may get by in stick construction but it does not work with these homes.

Other piece of advice is to put in a nice ERV or HRV depending on where you live.  I went with an HRV and immediately notice the difference in how fresh the air is- these homes are extremely tight!

I've seen online where you can get hvac calc for a 30 day trial and pay a small fee.  It takes a little time to input all your walls and windows but is worth it.

While the mini-split systems mentioned are nice, they are no IAQ standards to conform to (indoor air quality)- meaning they do NOT filter the air (that tiny drier lint screen doesn't count).  If you have allergies, I'd steer clear of them.  They are very efficient though.

Posted By Lbear on 22 Aug 2012 05:35 PM

Posted By Dana1 on 22 Aug 2012 11:00 AM

9.5 tons for 8000' that's 842'/ton, which is on the high side unless you have a lot of solar gain from windows late in the day. 

Out here in Phoenix Arizona on a 2-story (3,800 sqft), they will install two 5-ton units. One for each level. That is common practice out here.

Mostly 2x4, R-13 fiberglass batts, cheap stick frame buildings out here. $300 - $600 a month summer electric bills are average for Phoenix homes.

The old-school rule of thumb was 500'/ton, and even that was oversized for most houses.  By that rule of thumb you'd still be at only 8 tons, not 10, but bigger is always better when in doubt, eh?

Big leaky stick-builts in AZ with a great "sunset view" picture windows on the west side might actually see loads that big though.

BTW: Mike- I DO have allergies, and am still a big fan of mini-splits.  Running a big air handler with a restrictive filter is a crummy way to handle cleaning the air, and all of those houses with hydronic or steam heat somehow manage to maintain reasonable IAQ without them. Filering the ventilation air with the ERV/HRV is enough unless you have house pets with dander/fur issues. (And if you're allergic to THEM, no amount of air filtering with the HVAC is going to make or break it.)

Posted By mike597 on 22 Aug 2012 05:59 PM
While the mini-split systems mentioned are nice, they are no IAQ standards to conform to (indoor air quality)- meaning they do NOT filter the air (that tiny drier lint screen doesn't count).  If you have allergies, I'd steer clear of them.  They are very efficient though.

I used the Daikin ducted air handler, ceiling mount design, in a duct in the crawl space. The return air is ducted from the attic with a HEPA filter box in the downward duct. So yes, filtering the air with a mini-split system is possible, but not straight forward. I agree though, the wall units do not have much of a filter. I have one of those in the garage but filtering the air out there is not a concern.

Posted By mike597 on 22 Aug 2012 05:59 PM
I just finished building my home with ICF and couldn't be happier with the system I installed.  I do heating and air for a living, so the install wasn't bad.  What really stunned me was the numbers I came up with after running the house through "HVAC Calc".  The home is 4200 sq ft above ground w/ 1900 sq ft walkout basement.  That program was critical for proper equipment sizing.  I can't tell you how many guys I know that have done this for a living told me I'd be miserable if I only install a 2 ton unit for the second floor and a 2.5 ton for the first floor (ducts also feed basement to help dehumidify).


Other piece of advice is to put in a nice ERV or HRV depending on where you live.  I went with an HRV and immediately notice the difference in how fresh the air is- these homes are extremely tight!


While the mini-split systems mentioned are nice, they are no IAQ standards to conform to (indoor air quality)- meaning they do NOT filter the air (that tiny drier lint screen doesn't count).  If you have allergies, I'd steer clear of them.  They are very efficient though.

With two units (one for 1st and 2nd floor), did you have to install TWO HRVs or just one?
If you got some pics of actual air handler/HRV setup, it would be appreciated!

Did you do a blower door test?

I wish they would make a mini-split that would have better air filtration. While efficient, they are lacking in the filtration department. The aesthetics of the units hanging on the walls can be hard to overcome for some. They remind me of those machines that blow air at store entrances to keep the bugs & flies out of the store (aka - fly curtain fan door). I wish they would improve the aesthetics on mini splits.

                                                                  
                  MINI-SPLIT 

                                                                                                                                   


Bug/Fly Curtain Fan Door

How do you like your ICF home? It seems that the company that did your HVAC calcs really likes ICF over the other building methods. Where do you live?

(that tiny drier lint screen doesn't count). If you have allergies, I'd steer clear of them.

When I looked at different minisplits, they all seemed to have an air filtration system. The Daikin I got has some sort of photo-catalytic system as well as filters. Even the small unit moves 300 cfm which makes it a serious factor. Combine that with a filter on your HRV/ERV and you should be doing pretty well, even with allergies.