Another bad choices radiantec system questions

WildeRacing

Long story short,  I have a 1500 sq 7/8 tubing on 16". All other pipe is 3/4. I have a Taco 007e pump and a lowes Envo 27kw water heater. Now, before you reply about not having a boiler, I know. I have researched on this site and have reliezed my mistake. I plan on replacing the Envo with a Stiebel Elton boiler unless advised otherwise.

My building is not very air tight at the moment and I have very little insulation installed so it is difficult to determine the performance of the system.

Outside temp is 40 degrees
Building air temp is 60 degrees 
Floor temp is 70-80 degrees
I have 120 degree going in and 64-80 degrees coming out depending on circuit being measured. Outside circuit is the coldest. 

My question is how well is the system working. The heater is on all the time and i can't get it any warmer but the floor is pretty warm which makes me think the system is working well enough..
Should I return the water heater now and get the boiler? What about the pump? Or should i focus all my attention to insulating?

Thanks!

Hot_water_fan

That’s a ginormous boiler for that space! Is this a tent? 

What’s your electricity usage per month? You probably have low flow through the boiler. Do you mean 5/8 tubing? 

WildeRacing

Hot_water_fan said:

That’s a ginormous boiler for that space! Is this a tent? 

What’s your electricity usage per month? You probably have low flow through the boiler. Do you mean 5/8 tubing? 

Not a tent but vaulted and 14 ft walls. At the moment it is insulated as well as a tent.. I have only had the system running for a few days. The tubing is 7/8s.

hot_rod

How long are the loops?
His long has the system been running?
120 supply, 64- 80 return?
do you have a system design?

WildeRacing

hot_rod said:

How long are the loops?
His long has the system been running?
120 supply, 64- 80 return?
do you have a system design?

Longest loop is 260, shortest is 235. The system has been running for 3-4 days. What do you mean a system design? I have a loop layout.

Hot_water_fan

7/8 is pretty big for radiant, that’s why I asked. Also, since the loops are parallel to one another (I hope), they could be smaller than the common piping, since less GPM is traveling through each loop. 

WildeRacing

The loops are in concrete so I have to deal with that.

Jamie Hall

I note that the system has only been running for 3 or 4 days. How thick is that floor? It can easily take that long for such a floor to even begin to warm up, and I suspect that part of the very low return temperature readings is that the floor is still warming up. Give it some time.

That said, that low return temperature suggests very much that you could benefit from more flow.

hot_rod

Probably some high pressure drop in that tankless water heater, any spec in the manual on flow rates? Which pump setting are you using. A large pump may get you the flow rate you need.
Tankless water heaters are not often a great mix for radiant or hydronics.

Looks like a few loops are choked down?

clammy

Aside from other issues and question was the slab insulated properly . If not then it is no more then floor warming at best . At a Quick Look i would think that it should be piped primary secondary w a seperate pump for the heating loop and it’s a slab so I would think no more then 85 surface temp so if properly insulated that 125 supply temp sounds a little high . Even thought it’s a little late in the game where the manifolds that where used equipped w flow meters ? This would enable you to balance the loops easier and adjust flow in accordance to the lose of the area it serves . Usually on a slab system you want a closer temperature differential between supply and return any where from 7 to 12 degrees so as to have an even floor temp. Was a heat loss done on the structure or was it a hit and miss project . You may find that your floor will not properly heat your space on design and that a secondary stage is required . If your gonna try and get what you have working then do some reading on primary secondary piping even though I have my doubts that a electric wall hung hot water heater will function all that great under a low delta t being there designed for a wide delta and house water pressure to push it through it heat exchanger and The a radiant system works well w narrow delta as to produce even heat over a mass of area so it’s kinda a catch 22 . Tryin to get some to do some thing it wasn’t designed to do . Again I de start off w another pump on the loop side to lower that delta t across the floor loops
Peace and good luck clammy

hot_rod

You might check and see if there is a filter screen on that tankless heater that could be restricting flow, also.

HomerJSmith

3/4" copper pipe(?) in and out of the manifold is too small for a 7/8" pex tubing layout. Max flow thru a 3/4" pipe is about 4 GPM. If you don't have the heat energy delivery, your sys will under perform.
Two things determine heat energy delivery into a space, 1) supply water temperature, 2) flow. To increase the heat energy into the room, one or both must be increased.
People think that a larger tube will deliver more heat energy into the slab, not so. I only allows a longer loop and or reduced pumping requirements. There is not much difference in heat energy delivery at a given supply temp between 1/2-5/8 or 7/8" tubing.
I suspect that you are running out of heat energy before the water exits the pex because the water is moving too slow thru the pex due to the size. As stated by hot_rod, a larger pump would increase the flow which would increase the warmth in that room, but...you have 3/4" copper piping and when you increase the flow thru that piping you could get noise and pipe erosion and there may be other problems such as pressure loses in the heater, too.
You're delta T on the temperature gauges on the supply and return temp (more than 20 degs) may be very high and that would confirm my thesis.
As a personal note (I'm not raining on your parade) I was never enamored with the Radiantec sys. I did read their website years ago. To be truthful I only worked on one (not very popular in my area) a do-it-yourselfer.

hot_rod

Looks like a Y strainer next to the pump, might be good to pull that apart

It would be good to know the heat load i
of the space, as all these components get sized to that number 

us this a 1500 sq foot shop?
Did the tube layout include total gpm or supply temperatures?

GGross

Radiantec generally does not do load calculations, and so would normally not be able to correctly specify supply temperatures. They may offer that as an added service, but I have had several local DIY folks reach out to me requesting a manual J after radiantec had sold them the design and our local county building department wouldn't accept it without a manual J to go along with it

WildeRacing

The heater it supposedly rated for 4.8 gpm

Hot_water_fan

The heater it supposedly rated for 4.8 gpm

Oh boy. That's because it's a domestic water heater, so they rate it based on domestic water use. The GPM is irrelevant for your situation.

The room has a heat loss. Right now, you have a boiler that can provide 27kw * 3412btu/kw = 92kbtu. Which is 61 btu/sqft, normally an outrageously high amount. But we'll have to find out for sure.

Radiantec thinks you need 40 btu/sqft, but that's based on absolutely nothing, just a nice round number. If it truly needs 61 btu/sqft (or more), you're really pushing what a slab can do and you might need a more emitters, a second heat source and/or much more insulation and air sealing. Or adjust expectations.

You could very well need 20 btu/sqft or less. In which can you can meet that with a 9kw boiler. You'd use a 10 degree delta T, so only need 6gpm total, split across however many loops you have, on the coldest days of the year.

bburd

@Hot_water_fan's calculation above confirms that the three-quarter inch pipe to the manifold is too small. A three-quarter inch pipe can deliver about 40,000 BTU per hour at a flow rate of four GPM and 20° Delta T. The water heater is capable of more than twice that heat output.

hot_rod

I'm not concerned about the 3/4 copper. In a short circuit like that you can move 6 gpm with the proper circulator, and stay in a safe velocity range. 40- 50,000 btu/ hr could move through 3/4 copper M.

I'd like to think a 1500 sq ft shop would be around 30,000 btu/ hr. It depends on the temperature you want to maintain, in your temperature zone. Keeping a shop at 65F when outdoor is 40F is not a big load, assuming the building is tight and insulated.

If you want a simple, old school heat loss, here is the form and instructions. Fill it out and get back to us.

Find and eliminate bottlenecks.
Assure the boiler can ramp to the BTU you need after you do the load calc.

The 18" is workable. The heater maybe, maybe not. Possibly a bit larger circ.

GroundUp

1. Stiebel Eltron does not make a boiler, so you'd have the same mess you currently have if you swapped to the Stiebel. It's also a water heater.

2. It's piped wrong.

3. That water heater is WAY too big for 1500 sq ft, even with 14ft vaults. Like 3x too big.



If you're going to replace the tankless, replace it with an Electro Industries boiler. Possibly something of the EMB-M2-12-240-1 variety. Yes, the part number is way too long but that's what they are now. It'd fit perfectly in that space, and you'd just have to move the pump to the downstream side of the air eliminator and relocate the expansion tank to the threads in the bottom of the air eliminator.

WildeRacing

Thank you all for the suggestions.  I understand the heater is oversized but I'm not sure I see the issue with having an oversized heater? I would assume the larger size might support more flow and from what I gather the on demand heater I have now is too restrictive. 

What about a hydroshark? It's made by the same company stiebel? 

What I hear is I need more flow. Replacing the heater seems to be the first thing, the second look into a two stage system (need info on that). So if the system was working good.  What temp should the concrete be? 

Thanks again 

hot_rod

My suggestion would be to get or do a heat load calculation. Really no need to buy another boiler that is mis-sized both from a cost and performance standpoint.
You need an electric boiler not another tankless water heater. A number of manufacturers make radiant specific electric boilers with features geared towards your exact application 

The boiler ground up mentioned will adjust the boiler water temperature as the load in the building changes, there is no one specific temperature the boiler runs at, it will modulate to prevent short cycling and to match the ever changing load on the shop

Hot_water_fan

I would assume the larger size might support more flow and from what I gather the on demand heater I have now is too restrictive. 

Nope. Smaller is better and will not be meaningfully more restrictive. The difference between what you have and even a very small boiler head loss wise is night and day. Get the heat loss! And not from radiantec. 

What temp should the concrete be?

Not hot: maybe 80-90F on the coldest day of the year. Depends on heat loss of course. The better your insulation the lower the temp.

GroundUp

"HydroSmart" is just a cheapo knockoff company that puts their sticker on someone else's stuff and sells it as their own for triple the price. They don't actually make anything at all. The electric "boiler" they sell at Menards is literally a Stiebel Eltron water heater with a different sticker on it.

A properly sized unit will use less power and will have a much longer lifespan than something grossly oversized. I do agree that a heat loss calculation should be performed, but I'd be pretty confident in saying that a 1500SF space with any amount of insulation would not require more than 12kw. I heat a 1600 SF shop in MN with a 9kw Electro boiler and it seldom hits the second stage (meaning 4.5kw) unless it's well below zero outside. A 15kw or even 18kw in the same EMB line will modulate to meet the needs of the system without much detriment, since you already have enough power for that maybe oversizing wouldn't be the end of the world if you can't get a proper heat loss calc done. You have poor flow with this system due to the high pressure drop through the tankless, which is designed for a 30+ PSI pressure differential while you have only 1-2 PSI of differential because it's piped wrong.

So in recap, yes you need to get the space insulated and yes you should replace the tankless with an actual boiler (NOT HydroSmart/Stiebel Eltron) in order for the system to operate properly and efficiently. I recommend the Electro Mini Boiler (EMB) series as mentioned above- I've got several hundred of them installed across MN and have serviced several dozen more- they are bulletproof and in my opinion, easily the best in the electric boiler in the business. The floor temp should usually be 5-15 degrees higher than the air temp (depending on insulation) and there should be no more than 20 degree difference from supply to return. For example: a 60 degree air temp may be maintained with a 70 degree slab temp using a 90 degree supply and a 75 degree return. Those are hypothetical numbers, not an actual goalpost- however very similar to where I run both of my slabs at home.