Radiant Floor heating? Another question

camopants

So, I am looking into moving to Utah and buying some land to build a house. I am going to be doing a 40x40 insulated Quonset style building from Steel Masters on a concrete slab. I am trying to figure out what the best and most economical (installation and operation) way to heat the house would be. Is radiant floor heating with a Central Boiler corn/pellet stove a viable option for 40x40 2 stories? or would there be a better method of heating? any help would be much appreciated.

Eastman

Previous question

Have you posted before? Can you point me to the previous question thread so I can see where we are at?

camopants

Radiant Floor heating? Another question

No I have never posted here before.

Eastman

Climate zone

Do you know what climate zone you're looking at? What is the location like?

camopants

Zone

Well according to this map http://www.eia.gov/emeu/recs/climate_zone.html it would be zone 2 in mountain desert in Utah

Eastman

To cut it short

What kind of pellet stove are you looking at? Can it modulate the burner output?

camopants

Central Boiler

Looking at this one



it says water temp, heat output and air settings are adjustable. not sure if that is what you mean by modulate the burner output.



http://www.maximheat.com/maxim_features

kcopp

The pellet boiler....

is a fine idea... but why an outdoor one? Is Nat gas available? Slab on grade is great if insulated properly.

camopants

no gas

No, only utility to property is Electric. no gas or city water/sewer.

Eastman

As a point of reference...

By modulation, I'm referring to the ability to match heating demand with heating supply in a real time manner. If you take a look at modern mod/con boilers, you'll see that the output is variable. Usually the burner is capable of modulating with up to a 5:1 ratio. So if you are looking at a 100,000 btu max output boiler, typically it can automatically adjust itself down to 20,000 btu without occupant intervention. With modulation, the system switches off and on less frequently because there is a very wide zone where supply and demand can be perfectly balanced in real time. This saves major fuel and reduces cyclic wear and tear on equipment.



Correct me if I'm wrong, but the boiler your looking at comes in only one 250,000 btu model. It also utilizes a 90 gallon water jacket. At peak load, 1600 square feet in that climate zone should require at a maximum around 50,000 btu's. I've briefly looked over the Maxim boiler literature; they do not specify a minimum burn rate, but with solid fuels, I have a very hard time believing it could reduce to the range needed for your proposed project. And the 90 gallon water jacket would have to be roughly 10 times bigger to properly buffer such a supply/demand mismatch.



I am not familiar with pellet stoves, but certainly there exists modulating examples with suitable btu outputs. And there is no reason they can't be utilized with floor heat.



Couple of questions:



1. Have you you thought about how you are going to insulate this structure? The building envelope will dictate the size of the boiler.



2. Why a pellet/corn stove? Is this an off grid remote location? Do you want to utilize corn as a combination food/fuel?

camopants

Answers

Thanks for your response.



I was unable to find the minimum BTU of the unit. but it did say this in the brochure



"Heating Capacity - Self modulating and adjusts

between low, medium and high settings as the

heat demand changes . The M250 has a Btu

range of up to 250,000 "



I will call them tomorrow and see if I can get more info.



This is info on insulation.



"Insulation

• Blanket-style insulation easily retrofits after a building has been

constructed.

• Available in R-Values of 10, 13, 19 and 25.

• Standard roll widths are 48”, 60” and 72”.



The location is off grid which is why i am considering a wood pellet. I was considering a wood burning boiler but the location does not have a very hardy supply of hardwoods to use as firewood and pellets are cheaper that buying firewood.

I am also going to be adding a 40x40 garage and possibly another 40x40 building which I would like to run off the same unit.

Eastman

Couple things

First, almost certainly the boiler is oversized. If you call them, be prepared to interpret the salesmanship appropriately. However, that doesn't mean there isn't plenty of pellet stoves out there with suitable output ranges for your project.



Second, I suggest looking at building strategies that insulate on top of the slab. This makes the system more responsive. But more importantly, it also makes the wall/floor interface insulation system much more robust. This is particularly important for external steel structures like the one you're considering.



If someone tries to convince you to insulate under the slab because it will add thermal mass, tell them to buzz off. That is an outdated idea promoted to compensate for inadequate insulation, poor window fenestration, and on/off boilers. Build properly and don't buy an on/off boiler. Modern equipment has no problem maintaining 70 degrees 24/7, hence thermal mass internal to the building's insulation envelope is dead weight on the system and tends to be significantly out of sync with the demands of the occupants.



Now, that's not to say thermal mass is all bad. If you were to pile up dirt outside the building's shell, it would be exposed to the full temperature swings of the environment and actually have something to buffer. This would effectively moderate the climate as seen by the structure, reducing peak HVAC demands and creating a more even and comfortable indoor environment.

Eastman

For the garage

Many people run tubing in the slab. They don't insulate underneath because they don't intend to use it much which makes the added expense seem pointless. At some point during the winter they try out the slab heat and are disappointed at how long it takes to actually get the room warm. The system is working on it's own schedule and not yours, wasting energy all the way.



I think slab heat can work great in a garage. But it really works best if you only use it to keep the building out of the 30's or 40's all heating season. If you need the garage continuously, crank it up. But for intermittent usage patterns, I suggest paring it with a simple pellet stove for on demand auxiliary heat. Such a two stage system will give you quick response times with minimal btu wasting overshoots. And a mini-split for cooling/heating in the summer/shoulder seasons works great with an open floor plan.



Have you thought about incorporating solar into the system? Utah has some pretty amazing solar radiation levels. Using pellets all year long can be quite inefficient. Lighting solid fuel fires for small demands creates poor combustion efficiency and managing the pellet pile gets old. John Siegenthaler has published a variety of information related to such combination systems that you might be interested in. I also recall reading a posting from someone in Arizona that used a geothermal unit, but instead of pulling heat from the ground it was connected to large water store that was heated with evacuated solar tubes. I would imagine such heat pump based systems could be configured for a/c too.