Basement Radiant Floor System Boiler

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Mike Vavricka

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Hello, I am finally diving into utilizing the pex tubing in the slab for our basement versus the duct work from the forced air gas furnace. After finishing the basement last winter and spending more time down there this winter we would like to improve the comfort level during the heating season. I do not have split zone controls for the gas furnace, so with the thermostat being upstairs the basement is typically 5 -7 (and a bit more on really cold days) degrees F cooler then the set point upstairs. I would plan to close the damper on some/most of the vents in the basement during the heating season once I get this system running.

This is a walk out basement with a fair amount of windows/door and I did a heat load calculation and calculated 18000 BTU. I did the calculation based on 70 F indoor design temp using climate data for our area the country. The plan is to have the loops on one zone with one thermostat.

The main question I have is, are boilers like or similar to the ones below a good decision or am I going down the wrong path and should consider other options (electric boiler, gas tankless hot water heater, gas hot water tank style that is dedicated, or use a heat exchanger and have it do DHW and this system)?

I am confident in the calculations and other parts of this project; it is the heating source part of the project that I am not knowledgeable about.
My concern is that the coldest days in winter are the outliers and the average temperature is going to mean my BTU demand is going to be lower and the boiler will be operating for the most part around the lower end of a boiler output, versus the boilers upper end output. Do I have enough load for a unit like the ones below and their specs for typical days in winter so the boiler will run longer and not be turning on and off frequently?

I am sure there are other boiler options out there, but the ones below are some I have found so far searching and reading specifications that may work for me.

Westinghouse WBRUNG08W 8K to 80K The head loss is low so I think I would not need primary/secondary setup.
HTP UFT-80W (this appears to be the same unit as the Westinghouse) I was told the HTP UFT-80W is being discontinued but they have the EFTU-85WBN and ELU-85WBN. 8.5K to 85K and they have a circulator pump on board, The pump curves appear that they would handle the head and GPM for the boiler and loops without primary/secondary.
Weil-McLain AB-80-H 8K to 80K My quick first look at this one, and looses through it I believe I would do primary/secondary setup.

I am not against primary/secondary on any of these or other options, although it appears to me that if the boiler can maintain the output water temperature (give or take based on outdoor reset), the pump is sized correctly, this is not a zoned application, my thinking is that it is not needed for the Westinghouse or HTP units.

If more details would help let me know as I have GPM for system, floor temp to achieve room temp, head loss, and others calculated. I don't know much about gas boilers and the ones I see from dealers online mainly seem to be units meant for 15K and more for minimum rates and I think would be oversized.

Any thoughts or opinions would be appreciated.

Thank you,
 

Fitter30

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You don't need a boiler for such a small load could use a small gas water heater 30 gallon, a line voltage thermostat to cycle the pump, expansion tank, air separator and pump. With radiate heat have to use approved floor coverings and there isn't any better heat. Have any idea tubing size and lenght?
 

Mike Vavricka

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Fitter30, There are 4 loops of 1/2 inch, all 255 feet plus or minus a foot or two. The utility room is not overly crowded, so I would have room for a second smaller tank water heater for this. Most of what I would read online was referring to boilers and once I understood the heat load, I was not finding much for low BTU output gas boilers. I wondered how people who are not doing a whole house or a "larger" project are doing this and getting the performance out of a boiler, or being able to have it not turn on for short periods of time on each call for heat. I used vinyl plank on the floor, and Shaw had a average R value for there "family" of this product so I used that for calculations.

I assume you would plumb make up water to a tank water heater system, or maybe just keep a eye on things since you have a 30 gallon revivor and it should not fluctuate much, and add water as needed.

Thank you,
 
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