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Heating with forced air or water/radiant 1

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elfman

Mechanical
Oct 21, 2003
79
I am a mechanical engineer with a dilemma. I currently am heating a 2 story home with a 80% eff. forced air unit. The ducting is very poorly done. I have been doing a little reading on boilers/radiant heat. Boilers seem to be somewhat pricey, but I am thinking that the heating would be significantly more efficient. I am looking for some good design guides and installation guides. Also, what kind of overall efficiencies am I looking at with a boiler/radiant heat system?

Thanks in advance.
 
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With radiant heat you need to install tubing below slabs prior to pouring concrete. For second story amd up the tubing is installed between joists and a metal shield is installed over the tubing to increase heat transfer. You can find this info at Wirsbo or other mfr's sites for pex tubing. Radiant heat operates IIRC 95-105F. You can't run primary boiler water thru the tubing for various reasons, you have to use blending pumps. I can't give you efficiencies figures. For homes, I prefer hot water baseboard. For maintenance garages, I'd go with radiant heat for various reasons.
 
Elfman,

What do you mean when you say the ducting is poorly done? Is is undersized? Leaky? Not insulated?

If it is repairable, I would suggest staying with forced air, as it give you the option of adding central cooling as well.

You don't mention what you are using for fuel. With natural gas, either furnace or boilers are available with efficiencies greater than 90%. Condensing oil boilers are also available, and furnances may now be on the market as well.
 
I was trying to keep the question short, sorry.

The duct runs are very inconsistent in length. Some are only 4 to 8 feet and others are upwards of 30 to 40 feet. I have measured the airflow and some registers have literally half the flow of others.

I live in Salt Lake City, Utah so the winters can be pretty dang cold ( my opinion of course ), and the HVAC is in the attic where any and all escaped heat melts the snow on the roof forming ice damns in the gutters and eves. I was keep the cooling side of the unit for the summer, but switch to hot water/radiators for heating, where I can put the boiler in the living space and keep most the heat in the living-space where it is wanted.

We have natural gas for fuel.

 
Elfman,

All is not necessarily as it seems. Just because the measured airflow at a register has half the flow of others does not mean there's a problem; that might be the designed flow rate!

Regards,

Brian
 
I would tend to agree with you briand2, however, the temperature delta between the two floors ranges from 6 to 10 degrees F. I can't see a designer or an engineer designing a living space to have that much difference between the two floors. I haven't done my own heat load calculation yet, but I am pretty sure that it will show a some deficiencies in the design. Thanks though, I will take that into consideration as I analyze the system.
 
System may have never been properly balanced. A few balancing dampers might do the trick.

Are the ducts insulated? Is the ceiling insulated?

You might also want to consider replacing the existing single furnace with two or more smaller condensing units to achieve some zoning.
 
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