Author Topic: Need help designing a radiant heat system  (Read 193 times)

intellectsucks

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Need help designing a radiant heat system
« on: September 14, 2020, 12:50:55 PM »
Cold weather is coming quick to my area, and I have the time and money to install a radiant heat system in my house.

This MMM article (https://www.mrmoneymustache.com/2014/02/16/the-radiant-heat-experiment/) makes me confident that I can tackle the install, however it was pretty light on the processes that went into the DESIGN of such a system.

How do I calculate the size of such a system and it's components?

Thanks in advance for your advice and help.

intellectsucks

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Re: Need help designing a radiant heat system
« Reply #1 on: September 16, 2020, 02:57:14 PM »
Did some research and found what seems to be some useful info:

https://www.usboiler.net/heat-loss-calculator.html
Used this heat loss calculator to get an idea of what type of heat loss I'm using.  Here are my inputs from my measurements and their chart:
Length 77 (area1) 22 (area2)
Width 79 (area 1) 20 (area2)
Height 7 (area 1) 11 (area2)
Windows and Doors sq ft 78 (area1) 50 (area2)
Windows and Doors HM 41
Net walls HM 6
Ceiling HM 4
Floor HM 2 (I plan on insulating the floor very well when doing the install)
Infiltration HM 1.61

This gave me an estimate of around 114k BTU heat loss

Based on that, does this water heater seem like overkill (my house does not have gas, so I need an electric one)? https://www.homedepot.com/p/Rheem-Performance-36-kw-Self-Modulating-7-03-GPM-Tankless-Electric-Water-Heater-RETEX-36/300800822?source=shoppingads&locale=en-US&mtc=Shopping-VF-F_D26P-G-D26P-26_10_WATER_HEATERS-RHEEM-NA-Feed-LIA-NA-NA-New_Engen&cm_mmc=Shopping-VF-F_D26P-G-D26P-26_10_WATER_HEATERS-RHEEM-NA-Feed-LIA-NA-NA-New_Engen-71700000070895281-58700006241204832-92700056340155208&gclid=CjwKCAjw74b7BRA_EiwAF8yHFBo6OlziMol9sO8WCnWkF5qAebBwoN8Z-Bvs-R5VRD7NWfTbaDbacBoCNAAQAvD_BwE&gclsrc=aw.ds

How do I figure out what size water pump I will need?

If I overestimated my needs in either area (or if/when I improve my heat loss efficiency) will it cause problems for the components?

Thanks again for the thoughts and attention.

robartsd

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Re: Need help designing a radiant heat system
« Reply #2 on: September 16, 2020, 03:29:31 PM »
I'm not sure how to calculate your circulating water pump requirements, but it will depend on how you layout your system (size and lengths of tubing, number and type of joints) as this will determine the resistance to the flow of water. You need to figure out your target flow rate, calculate the resistance of your layout at that flow rate, then select a pump that will overcome that resistance.

I doubt that efficiency gains will be much of a problem for your system components. It should take enough time to circulate all the water in the system that I wouldn't be concerned about short cycling the equipment. The minimum on cycle length shouldn't really change with efficiency gains.

I'm interested in the type of system featured on builditsolar.com. Not sure if anyone there posted information on how they calculated the pump size.

Dusty Dog Ranch

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Re: Need help designing a radiant heat system
« Reply #3 on: September 17, 2020, 07:12:54 PM »
We did most of the radiant system at our former house (back in 2003), and our best resource (and where we bought materials) was the Radian Company. They are actually supportive of DIY folks. https://www.radiantcompany.com/