Ultra high delta of 60 degree fahrenheit

Shatter

Hello everyone,

I just installed radiant heat in my garage. And it turns out my delta t is 60 F wooow
Here are all the specs.
4 loops 250' 1/2 pex, thats what I bought but I wasn't around when they put them in, they might have cut them off a bit.
Grundfoss circ pump 3 settings running on 3
Rinnai RL94I
Temp supplied is 121 F
Temp return is 61 F
Trying to maintain a 61 F floor temp with a floor temp. sensor.
The Garage has 10f ceiling (R40) (walls R20) and is 30 x 32 with an 18 foot x 8 foot overhead door. Insulated man door and 4 windows about 6 sf per window. This building is a pole shed design. Concrete is on grade with aluminum bubble wrap underneath and 2" foam around the outside wall. We dug out a little footing which is like 2 feet deep around the concrete edge. I cant seem to find out why my delta t is so high. I know the insulation is awful, I been told that bubble wrap acts like R5.

I need some serious help here.

Jamie Hall

Bubble wrap at R5 is pretty optimistic. Leaving that be...

The delta T is related to flow and BTU delivered. If the delta T is higher than you want -- and I have to agree that 60 is a bit much -- there are only two other variables: flow and BTU. If you decrease the flow through your loops, your delta T will be less. If you push more BTU through -- not sure how you would do that! -- that will also cut the delta T.

Gordy

High deltas mean huge heat loss, or low flow rates, or both. I'm thinking both.

How long has slab been running?

Bubble foil is garbage. My as well have put it in a trash can.

Shatter

Well I exchanged the pump because first I was thinking there's gotta be something wrong with the pump. But turns out there wasn't.
Is there a possibility to increase the flow without problems and without putting too much $$$ into this?
The pump I'm using is a 15-58f.
The heater is rated to almost 10GPM flow.

I'm not a pro but it does look to me they totally screwed up on the layout of the pex!?

SWEI

Did they pull that rebar up during the pour? Where did your tubing actually end up?

Gordy

How thick is the floor pour? 6"? Tubing is at the bottom. Strike 1

No insulation of much value under slab. Should be R 10 strike 2

I see your running glycol. What % concentration 30-35 % max. Glycol reduces heat transfer, and is harder to pump.

So what you are dealing with so far is a big heat sink. Hot goes to cold. So you are warming the ground, and trying to heat the slab. Insulation stops this heat transfer.

Again how long have you been trying to heat the slab? This could take days. Especially with out proper insulation under it.

What type of boiler are you using? Or is it a tankless?

Gordy

Rebar is on chairs Kurt. Tubing is guaranteed at the bottom.

SWEI

Didn't notice that they used small bits of rubble instead of chairs. Ugh.

All manner of things can be made to work, but they must capture the bar in some manner to prevent movement during the pour.

Gordy

Sorry did not see the Rinanni in original post.

It's a tankless.

You voided the warranty using glycol.

The pressure drop through the heat exchanger is astronomical. This has to be considered when sizing the circulator.

SWEI

Also no ODR control on a tankless water heater, which will make it essentially impossible to control that slab.

Gordy

Gordy

You will need a mining pump to push 10gpm@ 60' of head plus pressure drop of pex loops, an piping. Ain't going to happen.

Zman

With the lack of downside insulation and the tubes at the bottom of the slab,it is going to take quite a bit of time and energy to get up to temp. You will eventually get there.
Your water heater has a fairly big head loss. You may have to go with a bigger circulator like the 26-99.
Can you tell what % the heater is firing?

Gordy

The tubing layout at the garage door should of had a lot more density for sure. The rebar I hope stayed on the make shift chairs, and did not fall, and crush tubing during pour.

Zman

With the lack of downside insulation and the tubes at the bottom of the slab,it is going to take quite a bit of time and energy to get up to temp. You will eventually get there.
Your water heater has a fairly big head loss. You may have to go with a bigger circulator like the 26-99.
Can you tell what % the heater is firing?

Shatter

To answer all the questions,

yes they did pull it up during pour, the piping should be between 1/2 and 3/4 of an inch floating on the bottom of the slab.
The slab is between 5 and 6 inches.
The glycol is a 50/50 polypropylene mix.

So whats the smartest to do about my situation now?

Oh outside temp is 10.4 F at the moment.

Gordy

Basically your high delta is due to heat loss no insulation, and flow rate mostly do to the high head tankless. Even at 6 gpm your at 30' of head that pump you have won't get it.

I'm thinking the bell and gosset NRF 36 speed 3.

Shatter

Ok there's one option. What about lowering the PSI on my loop. Currently I'm on 25PSI.

Gordy

Get the glycol down to 30-35%.

I don't think the 26-99 will get it.

What temp are you looking to keep the space at?

Gordy

Psi has nothing to do with flow rates. You should only need 12 psi though. Unless the tankless has a minimum psi. To operate. I have not completely read that manual.

CMadatMe

We're dealing with a Tankless Water Heater here not a boiler.

Check for proper water pressure to the water
heater. Minimum/Maximum water pressure is
20-150 psi. Rinnai recommends 30-80 psi for
maximum performance.

Last I knew a heating system runs at 12lbs. At minimum needs to be piped pri/sec, increase system pressure to 15-17lbs, adjust exp tank pressure. Nothing about a heat loss in the post but I'll stab at around 20,000 when the door is closed. So flow rates on the radiant around 4gpm total.

You'll never get 199,000 btu/hr out of the unit. You'll be at the mercy of the flow rate of the boiler pump once you get it piped primary/secondary. Shoot for 6gpm across the HX. Could get away with a UPS15-58 on Speed 3.

Keep this in mind too..
Period of coverage is reduced to 3 years from date of purchase when used as a circulating water heater within a hot water circulation loop, where the water heater is in series with a circulation system and all circulating water flows through the water heater, and where an on-demand recirculation system is not incorporated.

Didn't see the glycol in the mix. Oh boy.... Get rid of the tankless and use a boiler that is designed for the job as Harvey suggests.

Harvey Ramer

The cheapest and best thing to do is to pull that on demand water heater out of there and put in a Modcon boiler. You will be in a fist fight with that water heater till it's finally beyond repair. It will end up costing you more.

Shatter

Ok the heater runs on 12 to 15 no problem I would say. The heater didn't complain when I had it running that low for a few minutes.
I'd like to keep it around 60-65 air temp, that's all I'm asking for.

Harvey Ramer

I repeat myself.

Shatter

Didn't see your post before I was answering Harvey.
Would that heater be good for using it in the house as a water heater still, since I used it for a little bit with propylene glycol?

Harvey Ramer

Propylene glycol is one of the main ingredients in Vape products. The vapers aren't dead yet. They are working on it though. It's also used in Fogg machines at the clubs. Those people aren't dead yet either.

I would still thoroughly flush it with a sanitizer. Then it should be good for domestic use.

Gordy

Chris the tankless has 20' of head @ 6gpm the 15 58 won't do it.

The NRF 36 will work on speed 2 . 6 gpm at 20' but he has glycol, so speed 3 has some cushion. Same pump.

But I'm with @Harvey Ramer on getting rid of the tankless if OP is willing to buy a boiler.

Shatter

Ok sounds good. But now there comes up my question.
So my only real big problem is that I ended up buying a heater instead of a boiler? Besides the poor insulation...
I cannot find any Modcons here in Canada.
Is there anything like Rinnai or Vossmann with a vent system similar to the one I have, so I dont need to cut more holes in the shop?

Shatter

How long would my heater lat with a bigger pump? If I would get 10 years out of it I'd be happy.

And what about this pump Grundfos 52722512 3-Speed 1/6 Horsepower Circulator Pump with Flow Check instead of the NRF 36?

Gordy

Look at Rinanni Q series

Harvey Ramer

Here you go.
https://www.rinnai.us/boiler

That will be your closest fit.

Shatter

Thank you guys for your help so far.

Did you notice my last post? So if I decide to go with a boiler instead, at what BTU range should I be looking for?

Gordy

Shatter said:

How long would my heater lat with a bigger pump? If I would get 10 years out of it I'd be happy.

And what about this pump Grundfos 52722512 3-Speed 1/6 Horsepower Circulator Pump with Flow Check instead of the NRF 36?

The 26-99 will be close on speed 3. Reduce the glycol concentration. The problem I have is the glycol through the tankless. It reduces heat transfer, and is more viscous.

Those head values are for straight water.

Harvey Ramer

Shatter said:

Thank you guys for your help so far.

Did you notice my last post? So if I decide to go with a boiler instead, at what BTU range should I be looking for?

You need to do a heat load calculation to determine that. Are you familiar with the process?

Shatter

Not really, I did try to look into it but couldn't wrap my head around a lot of things as far as I can remember.

Gordy

There is not a lot to it if you use the slant fin. It won't be perfect with that calculator, but it's user friendly, free, and will get you in the ball park.

Harvey Ramer

I can do one for you if you like. It won't be for free and we don't discuss prices on the wall, so you'll have to private message me if you are interested.

SWEI

Do the math, but you probably want the smallest size gas boiler you can get.

What are your prices for gas and electricity like there? A small electric boiler could make a good fit.

To make that tankless work properly would require a buffer tank, another pump, and a motorized mixing valve. Together they probably cost more than the tankless did.