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Heating & Air Conditioning

radiant floor heat

10 years ago

new 40 x 60 x 16 steel frame building. r-17 insulation in walls and roof. radiant heat in slab on grade. north central u.s. quite cold here at times. hot too.

one half of the building is garage/shop. the other half is living quarters. one level: kitchen, bath, bedroom etc.

rural area-- no gas, all electric. 11 cents per kw hour. propane cost is high. I have a well but don't want to do geothermal for this project.

two zones for the radiant heat. one for garage, one for living space.

just one person living there for the most part.

questions:

which is better for this application, a water heater or boiler? what are the considerations? i'm thinking i'd keep the garage part around 60 in winter.

2. for the a/c and supplemental heat in the living space, what is the best option? it's about 1200 square feet, all on one level and pretty open. 10 foot ceilings. just the bedroom and bathroom are enclosed. what about these inverter heat pumps?

thank you.

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Comments (3)

fsq4cw
10 years ago
IÃ¢ÂÂd say the short answer is a boiler for hydronic in-floor radiant and mini-split HP for A/C & heating redundancy. Perhaps some ceiling fans as well.

SR
Elmer J Fudd
10 years ago
I'm a homeowner, not an expert, but doesn't an electric boiler rely on resistance heating? I don't care how efficient a hydronic system is, I think that will be very expensive to operate. Your HVAC contractor should be able to help you assess how to balance initial costs with operating costs.

An alternative to consider would be an air-source heat pump, the line designed to do better than competitors in lower and sub-freezing temps. (One of the regular experts will supply the name). Along with a high-eff propane furnace as backup for the extreme temps. I'd put the ducts on the inside-side of the walls in bulkheads (also called "inside the envelope") to improve efficiency and reduce heat/cooling loss to the outside.

Since this is a new building, be sure it's tight, has plenty of insulation, and that the steel structure has thermal breaks so that heat and cold aren't conducted inside by the skeleton.
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Based on my experience, I'd say that trying to divide an open area into two zones won't work. We built a 1000 sq ft addition of several rooms and and an open area - it has its own furnace and a new furnace was put into the existing structure at the same time. The connection between the areas is a wide-ish hallway. When both furnaces are on, the house is evenly warm. Without closing doors, it's not feasible to have the heat on on one side but not the other because the cold air mass on the "off" side keeps the "On" part of the house from warming up. The areas most distant from the border will get too warm as the system tries to compensate, and the areas near the border stay cold. Neither cold nor warm stays put because you want it to. In your plan, I think there would be a constant flow of warm air to the cold area along the ceiling and cold air to the warm area along the floor. Not a question that you asked, but your plan suggests you're going to have a very dark region by the dining room and stairs. You've got a long wall with no windows between the living room and the family room, and the fireplace will block light coming from the front. Good luck
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The best approach for both locations is the one that your hvac and general contractors are most familiar with.
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ionized_gw
10 years ago
I won't do the calculations for heating with propane vs electric. If you are going to heat with electricity why heat water first? Can't the electric heat be buried in the slab? If for some reason some other fuel source becomes less expensive, install forced air using that.

On the other hand, a heat pump producing hot water could serve you better in the long run for radiant heat in the slab. I am not an expert, but my impression is that is more a commercial-type installation. I know that Mitsubishi City-Multi systems and similar from other manufacturers will make hot water, but they may be too big for your building. There are probably other options, but they might be outside the experience of a strictly residential installer.

Carefully consider building orientation and window location for passive solar heat in winter. If you have good insulation and other efficient features, a high efficiency heating or cooling system is less important and you will have to invest in smaller mechanical systems.

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