Can I Feed Radiant From Return to Boiler?

[strmh]

Right now I've got an EKO 60 in my shop that is connected in series to my oil boiler in the house. The circulator is on the return at the EKO and runs full time.

My shop is piped for radiant heat, but I'm not exactly sure how to feed the radiant from the EKO because I'm always pumping to/from the house.

Since radiant calls for lower temps, would it be possible to just pull from the return to the EKO?

 

[stee6043]

You'll want a mixing valve I suspect. If you're EKO is running properly your return temps should be in the 150-160 ballpark most of the time which is still too hot for most radiant applications. Do you have a manifold for your radiant? I assume you have more than one loop?

You'll probably want to plumb off your supply to a new manifold with the proper mixing valve(s) for your radiant. Having them separate will be nice when you don't need to be heating your shop...

 

[strmh]

Thanks for the input.

As far as pulling from the supply side......do I need to worry about stealing heat from the house? Right now my EKO circ is always running and it's a direct feed into my oil boiler......i was concerned that if I tapped into the supply side, i wouldn't get all the hot water that was needed for the house.

Again, I appreciate any additional insight.

TH

 

[stee6043]

How much heat is "left" for the house will depend entirely on how much your take away. It sounds like a little math will be required. How much total flow do you need through your radiant zone and how much do you need through your oil boiler in the house?

Have you done a heat loss calc to make sure the boiler puts out enough BTU to heat both?

The heat loss calc is probably the easiest place to start. Determing the flow through your oil boiler and radiant zones and comparing that to your current circ output and current plumbing configuration might get a little more complicated.

 

[strmh]

OK, I did the heat loss calc when I bought the boiler......I worked with AHONA to size the boiler and I think I'm good there.

I guess the true source of my concern is water flow.......if I pull from the supply to the house, will that compromise the flow to the house? Sad to say, but I do not have a strong technical understanding of hydronics and how water will flow. I want to be sure that with my current set-up of one main cric at the EKO, I can pull for the radiant in the shop and still keep a good flow to the house.

Thanks for the help.......

 

[Chris S]

As most hydronics trainers will say " water is lazy, it will take easiest path" So if you take supply side water from your eko, you could take some of the flow (gpm)away from the house, without re- piping etc.
On the other hand if you take it from the return side, you could risk dropping the boiler return temperature into a range you don't want to be in. I'm trying to envision a simple boiler piping scheme here.
You should definitely use a mixing valve, or injection system to control the temperature of fluid going into your slab. Most of our in slab jobs run under 100 degrees.
If your eko return pump is running all the time... what kind of temps are you putting back into the boiler? You may want to look at this first to avoid future problems.
Did this help at all? or am I just rambling?

 

[strmh]

Chris,

Thanks and I've got a Danfoss mixing valve keeping the return temps >=140 degrees.......if I were to pull my radiant off the return, it would take place prior to the Danfoss to ensure return temps are maintained.

I definitely plan on controlling the temps going into the slab...90 degrees or so.

With that said, does supplying radiant from the return sound feasible??

 

[ewdudley]

.....if I were to pull my radiant off the return, it would take place prior to the Danfoss to ensure return temps are maintained.

I definitely plan on controlling the temps going into the slab...90 degrees or so.

With that said, does supplying radiant from the return sound feasible??

It's certainly feasible and I would argue it would be preferable.

Using closely spaced tees on the wood boiler return line, just run the shop load with a separate circulator that pulls through a mixer valve. You need a separate circulator to run the shop load mixer circuit anyway.

You might want to add an aquastat upstream of the closely spaced tees that feed the shop load. This aquastat would disable the shop load circulator when the return temperature from the domestic loads is too low to do any good for heating the shop.

I'm not sure if I have a complete grasp of how the main cirulator is set up to run through the oil boiler, but it seems like it should be possible to turn off the main circulator if the oil boiler is hot enough and there is no call for heat to the shop load.

Cheers --ewd

 

[btuser]

How big is your shop? If you control the delta coming back from the slab you can limit the amount of heat stolen from the house side. How big/far are the lines going to the house? What's your typical supply/return temp on that loop?

 

[strmh]

btuser,

I plan to heat around 1800sqft.....(average of 10 ft ceiling)......

I've got 210' of 1 1/4 Thermopex (420' round trip) and the supply temps are usually at 190-195. When there's no call for heat in the house, return temps almost equal supply, however they do drop to 140-150 when it's cold.

ewdudley,

Good idea with the aquastat.

 

[in hot water]

The return temperatures when it's cold indicate the home is using most of the heat energy the boiler is providing, and / or you have some large losses to the colder ground. The boiler needs 140 or so to stay above condensing operation, it may not have enough energy to provide for additional loads.

It would be interesting to know the temperature drop from the boiler to the home under cold conditions. Also the return temperature at the house, then at the boiler. This would indicate how much is transmission loss and how much is going to the load.

As far as the boiler is concerned it doesn't know if the additional load is taken from the supply or return. But the new load may drop the temperature to the house load beyond an acceptable temperature, if taken off first on line. Cold concrete slabs will overpower most boilers on startup, it has a lot of mass to accelerate.

If the boiler is borderline on sizing you might configure the control logic prioritize the load and maybe include outdoor reset control.

hr

 

[Donl]

Why not just simply use a couple of tees off the return line and create a secondary loop to the radiant floor. The secondary would consist of it's own pump and mixing valve. If you want, you could place an aquastat on the return line just before the first tee that will only allow the secondary pump to turn on if there is adequate heat available. Seems like a simple approach to me.

 

[in hot water]

Yes, P/S (primary/ secondary) is always my favorite approach. The main loop pump would need to run to make P/S work. Sounds like that is the case with a series, boiler piping?

hr

Here is a link to an article that may help.

www.pmmag.com/Articles/Column/69285e1f0bfc7010VgnVCM100000f932a8c0____

 

[strmh]

Yes, my main loop pump is always running and after reading the article, I like the idea of a P/S on my return. I feel better knowing that the house will not be robbed of a good supply of hot water.

Thanks to all for the help.

TH

 

[btuser]

What temp do you want to heat your garage? With return temps in the 140s I suspect your boiler is the propper size for your house. I'm sure as long as the house has priority you could pull enough to make it comfortable in all but the coldest weather. My 1st thought would be to add storage as kind of a battery so you could maybe get longer burns, but a slab is in effect a big thermal mass so it may not be needed. Not that a 70 degree slab is going to make up for storage but if the house pulls all the heat for a couple hours a day during the coldest weather your garage won't really suffer.

You're going to have to mix anywa, so I don't see the benefit between pulling from supply or return. I'm also guessing the shop is going to need is own circulator. You may want to go off the supply, so you're not heating your lineset to the house when/if there's no call for heat from the house, and pipe in a P/S as suggested already.

 

[bigburner]

1 pump, a pair of tee's & an auqasat with a mix valve. The biggest concern is shutting of the floor in the shop, you will find that both boilers can dump in to that floor and it will takes hours to reach a few degrees on the set point. You will not want to have it set to more then about 62 if you are working in there any way. It will take time to heat up, but best of all it will take time to cool down and that's when/why you shut off the floor during low return water temps. "my opinion"

 

[strmh]

While we're on the topic, can anyone offer any advice on the best radiant manifolds to use? Pex Supply has a few models, but I really don't have any idea which ones are best. I don't have any pex related tools, but plan to purchase what's necessary.

 

[bigburner]

if you are only doing a single job, skip the tools. We have done bunches of in floor from 3 loops to dozens and tried every variation of components. If you like to sweat use copper fittings, if not black/galv pipe works just fine also [closed system]. we had great luck with using shark bite fittings on the loops. I just lay out all the components on a board and sweat them together hang it on the wall, plug in the lines. I use lots of valves, boiler drains at the end of each manifold shut offs at the start of each manifold and any where else isolation may be needed. Big fan of power purging out the air using domestic water pressure. Not sure if you said floor was done yet but if not, In our area water table can be 10 feet down or more, if so on bigger jobs we only do Perimeter insulation. 300 ft loops of 1/2 pex tied on 24 inch centers, smaller jobs we will move it closer to 12 inch. We still tie it all to 6 x 6 wire mesh or re-bar if heavier traffic. Also remember to sleeve it coming out of the floor using 3/4 PVC conduit sweeps.