DIY radiant heat control?

[Thrifty1]

Hi. I’m new here. Was referred by a friend that this is one place to get information.
I’m building my own hydronic control panel, kind of copying one for sale for too much at big box. I’m reasonably competent with soldering and mechanical stuff.
Was wondering if anyone has input on my project. I’ll eventually add a outdoor boiler but will start with lp tankless water heater.
I’ll have 4 zones. Zone 1 is 2x300 feet of 1/2 “PERT in concrete over 2” foamboard. That is the beginning and I need the mechanicals soon.
I’ve had suggestions of using a programmable logic control in lieu of zone valves. Make sense?
I’ll try to add the design below and would greatly appreciate any input from knowledgeable parties. Thanks in advance. Tom

 

[PassionForFire&Water]

All you ever need at your fingertips .....

Magazine archive

From this page it is possible to download all Hydraulics numbers in PDF format.

idronics.caleffi.com

 

[gthomas785]

Does your tankless water heater have a low enough temp setting for radiant? you'll generally want <120F and probably closer to 100F water if not you can use a mixing valve to mix some of the return water with the supply to achieve the desired temp. Even if you don't need a mixing valve now, you will once you switch to the wood boiler.

Also, what will your "programmable logic control" be controlling exactly? I believe you would still need either zone valves or individual zone circulators to accomplish the zoning.

 

[Thrifty1]

Thanks. I’m assuming I’ll have to get a mixing valve. Another suggestion was a buffer tank which I’m guessing is a tank style hot water heater so the rinnai doesn’t run all the time.
The logic control was another suggestion but I know nothing about them. I’m going with eventually 4 zone valves.
I appreciate your input. Tom

 

[hedge wood]

Thrifty1 First off welcome to the forum. I will give you a quick run down on my in floor head in my shop 30x60 with 16 foot walls. I have no zone valves. My supply's tubes all go to a manifold and my return tube's come back to a manifold. In the beginning I used a 40 gallon LP water heater. Just used water in the heater. Went to a heat exchanger I had glycol on the floor side of the heat exchanger. Mixing valve ,pump , expansion tank on that side also. I used a Ranco controller to turn the two pump on and off for temp in the shop. It worked well. When I installed the Garn I took the hot water heater out and pump hot water out of the Garn to the heat exchanger now. Nothing else in the system changed. I think you will find tankless heaters don't work for floor heat. Had a buddy try one and it didn't work out. He went to a tank type LP boiler. I don't know why you would want zone valves. Floor heat is like a flywheel once you get it going you want to keep it going. I just use the Ranco to cycle the pumps to maintain the temp in the shop.

 

[Tonty]

If you do want different zones, I was told a pump for each zone was better than zone valves. Something about the zone valves not lasting very long. I don’t know if that’s true or not. I have three different zones and did go with a pump on each one.

 

[gthomas785]

I don't know why you would want zone valves.

Just so we're clear. Zones are for separate spaces you want heated, but a single zone can have multiple pex loops. It depends on what space you are trying to heat.

Also I've never heard that tankless heaters don't work for radiant? In my experience as long as you match the BTUs reasonably close and get the water temp where you need it a tankless will work very well.

 

[hedge wood]

Just so we're clear. Zones are for separate spaces you want heated, but a single zone can have multiple pex loops. It depends on what space you are trying to heat.

Also I've never heard that tankless heaters don't work for radiant? In my experience as long as you match the BTUs reasonably close and get the water temp where you need it a tankless will work very well.

That would be correct on the multiple pex loops. I have many loops in my 30x60 shop and they all go to a manifold and are all feed from one pump and one inch pex. My whole shop floor is a so called one zone. Both guys I know that tried tank less heaters couldn't get them to cycle the way the heaters needed to to run the floor heat. Give it a try and see how it works for you. You may get it to work. Both of these set ups were installed when tankless heaters were new. One went to a waste oil boiler and the other went to a LP boiler. Both are farm shops.

 

[gthomas785]

I think some older tankless heaters had a pretty high minimum flow rate, ie if you just trickle water through it would never kick on. So that is something to check, that your flow rate is in the range of the water heater. Also, if the heater BTU rating is oversized then it may not be able to modulate down enough and shut down on a high limit. Remember they are designed to run a pretty high delta T which you may not have in a radiant system, so the BTU you need for a given flow rate would be much less than in a domestic hot water application.