Hi all, I'm building a 2200 sq. ft. PU-SIP 2-story house in Calgary, Canada that will be using Geo-Exchange for heating.  The heat load calculated by the consulting energy modeler was 51k BTU/h.  My options for distributing the GeoX heat are:

1. Forced-air to the main and upper floors.  Basement will be plumbed for hydronic heat.  So a combo unit such as the Nordic TF series would work.  This would also allow for cooling, but cooling load is negligible during our dry and mild summers.
   
2. All radiant in-floor heat using Warmboard on main (oak hardwood)  and upper (cork).  A liquid to water unit like the Nordic EM series would work.

For my particular situation, the upgrade to option #2 (three-floor radiant) would add about $25-$30K (CAN) to the house price over option #1.  I would appreciate your comments on the following questions:

1. Is the radiant upgrade worth the $? I know this is a subjective question, however I've heard that radiant is much more comfortable than forced-air heating (in general).  However, in a well-insulated home with a low heat load this benefit has been described as minor (read elsewhere on this forum).  Is this because:
•  the lower required hydronic water temps limit the floor's feeling of "warmth"?
•  while the tight insulation limits the hot/cold spot issues one gets with a poorly insulated forced-air house?
2. The GeoX unit specs seem to indicate that liquid to air is more efficient than liquid to water.  (Perhaps I'm not interpreting correctly).  If so, is the "greener" approach for GeoX to use a forced-air unit?
3. My guess is that Calgary's cooling load is too small to factor into this decision.  Anyone out there in a similar climate who finds they're making good use of their GeoX forced-air system's cooling ability?
   

Any other comments/questions you have on this choice would be most helpful.

Thanks much,
Guy

We live in a SIP home with radiant floors (ours are concrete). I would not give up my radiant. Warm feet and cooler air at the head level makes me much more comfortable.

Radiant is great, but efficiency issue for geo is than your heat load isn't so ultra-tiny for a 2200' house it works out to 23btu/ft^2, which means you need to really work it to get the water temp down to where the geo can make it efficiently (typically under 110F). Not sure if it can be made to work that low with Warmboard. With slabs, probably.

How much is the Geo costing you? Dana has a point that for 2200ft^2, your heat load seems a bit high. Maybe a lot of windows?

Anyways, have you priced out the cost of using a conventional heat source for the radiant instead of Geo? With the Calgary climate you payback may be quite a long time, especially if you can reduce some of that heat loss.

Thanks Dana and Kicker, good questions about the heat load.  House will be R44 PU-SIP walls, R60 cellulose attic, R-10 rigid on basement wall/underslab with R-20 bat inside.  Windows will likely be triple pane though the heat load calcs may have been done with dual-pane on south and west.  I'm not sure the % window area compared to sq. ft., but I don't think it's significantly higher than an average home.  One thing to note is that we'll have a total of 4 standard (swinging) doors for the house (front, basement suite, back, and deck).  We'll have two HRVs for ventilation (basement suite requires its own by code).

The radiant contractor came up with a number of about 60k BTU/h.  He showed me room by room calcs, but I didn't get a copy.  The 51k BTU/h number was done by an energy modeling consultant based on our final building plans.  I'd be surprised if they are wrong. With SIPs etc we were clearly striving for a very tight envelope.  What kinds of BTU/h numbers should I be seeing?  Aren't these calcs heavily dependent on climate?

Natural gas is cheap in this province (this year anyway), but I'd prefer the GeoX route for its green characteristics.  Radiant contractor quoted about $11K (CAN) for a "beefed-up" demand heater that could handle three-floors of radiant.  As well, for $24K (CAN) we could go with a mod/con boiler.  GeoX options start at around $31K (CAN) and helps qualify for a $10K "Green" provincial grant.

Warmboard can hit lower temps than many slabs, assuming both have finished floors over them. it's an excellent choice for low temp heating.

for a house of your construction I would be surprised to see more than 10 to 15 BTUs/sq ft peak load, though the amount of your glass will influence that heavily, even in a very cold climate. you don't seem that cold, about the same as maine perhaps. 60k for 2200 sq ft of superinsulated house seems wildly high... again, unless you have lots and lots of glass.

http://www.climate-zone.com/climate/canada/fahrenheit/calgary-springbank.htm

http://www.climate-zone.com/climate/united-states/maine/caribou/

http://www.climate-zone.com/climate/united-states/maine/portland/

Calgary's a lot colder on average than coastal Maine, but not as cold as Caribou, possibly similar to Millinocket for averages(?).  But these are averages.  Peak loads in Calgary can be pretty extreme when the wind is out of the north & northwest (it's not downwind of the moderating influence of Hudson Bay & N.Atlantic the way Maine is- it's downwind of Yukon,NW Terr. & AK.)  This January's cold snap saw several days in a row of -15F (& lower) lows, where the daily highs barely made it past -10F:

http://www.wunderground.com/history/airport/CYYC/2009/1/19/MonthlyHistory.html?req_city=NA&req_state=NA&req_statename=NA

But this wasn't an extreme winter.  It dips below -20F a handful of times/winter most winters, sometimes well-below.

What is the design temp at which you're looking at 51KBTU/hr?  -20F? -25F?

Those temps are comparable to what we see on the ground here in central maine. in my area, I would expect the numbers I gave to be accurate and certainly within 10 or 15 degrees of outdoor design temp the shift is only 15-20% or so... 2 or 3 BTUs/sq ft fudge either way here, not 20 to 30.

When you say 2,200 sqft, is that including the basement? I'm a bit confused since you say two story home, but then mentioned a basement suite?

When they did the heat loss analysis, they shoudl have broken it down into how much loss is due to windows, slab, attic, walls, air changes, etc. You might want to look at that to determine where to spend your money wisely.

You might save a lot more by using a cheaper heat source and adding things like cellular blinds, or upgrading the slab insulation.

I'd have a hard time seeing that Mod/Con paying off if it's an extra $13K to install!


Your max design load is 51k BTU/h, but was is the annual loss? This will be based on how many degree days of heating. I lived in Calgary for a couple of years, and while it gets cold, the average heating load during the winter is not all that high, especially with the chinooks.

Good questions Kicker.  I'll answer what I can.  I was using the local realtor sq. ft. practice (silly really) that ignores below grade space.  So upper and main floors alone are 2200 sq. ft. (split about evenly).  The basement adds another 750 sq. ft. of finished living space with another ~200 sq. ft. for a mechanical room.

The energy modeling report lists 108.3 million BTU (per year?) as the "Total Fuel Consumption" to put perspective on the 51k BTU/hr heat load.  The report doesn't include the heating degree days (or the base temp) used to arrive at those numbers unfortunately.

I agree that Calgary winters are generally mild as I normally cycle to/from work all year round, just adding some studded tires when snow is on the ground.  We do get the occasional cold snap though that can last a week or so with high temps of only -30C (-22F) so I guess the heat load needs to handle the worst periods.

I don't mind paying a bit extra to get a "greener" approach to meeting those heating needs, even if payback is very long or never.  We'll likely be in this house for 20-30 years.  The challenge is determining whether GeoX is really a green option in this province with our primarily coal-generated electricity at 8cents/kwh.  Thanks for the comments.

Just spoke with my builder and I have been misinterpreting the energy modeling report which reported heat-load numbers for a similar-sized home using standard insulating techniques (not as good as the actual SIP home I am planning). This baseline was used for comparison to my planned home. Unfortunately, I don't have accurate heat load numbers yet for the actual house. Soon...

So, back to my original question. One vote from jmagill (above) that radiant heat even in a low-heat load SIP house is still worth it. Any comments from someone who went with forced-air in a SIP home and has no regrets?

If I had a builder needing an extra $13,000.00 to install a mod con boiler I would ask him/her to justify the additional cost and look for a different quote.
The cost difference flash water heater next to a mod con boilers is substantially less more along the lines 1 to 4. Further most mod con boilers have a host of built in features not provided with a flash water heater.
Dan

THAT explains a lot.  Don't be surprised if your actual peak heat load is under 35K.

Given that the peaks in Calgary are far higher than the averages, odds are pretty good that your geo can run efficiently most of the time, and you can use electric resistance to back it up for the cold-snap peaks.

Odd are you won't find many people who went with forced air looking at this forum- you might pose the question on the geothermal  or SIP forums.

Geothermal exit air is significantly cooler than it's distant fossil-fired cousins (tepid at best)- duct design, air velocity & register placement factors are HUGE when going that route.  Done right it can be quite comfortable, but it never has that cruisin' in yer socks appeal on frosty cold days that radiant gives you.  How much the latter is worth in dollar terms is, as you say, highly subjective, and in truly superinsulated homes you'd have to cut back on the radiant area a bit to get the temps up in the places where you might sit/walk to get that effect (which cuts back a bit on geo efficiency as well.)