Need input on fairly new PEX heating install

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  #1  
Old 07-16-14, 05:26 PM
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Need input on fairly new PEX heating install

We have a small 800sqf summer home(new construction) with a Rinnai propane system and PEX piping. During the winter the house takes forever to heat, we keep the heat at around ~40 degrees and crank it up on our way to the house (over WiFi) it takes a full day to bring the heat into the 70s.

I decided to call a heating guy, he told me that the water is leaving the boiler at 180F and coming back at 180F shutting the boiler off. He starts poking around and noticed the PEX to baseboard is 1/2 instead or 3/4. Is 1/2 diameter the wrong size coming into the baseboard?

I ask because we thought about replacing the baseboard with high output baseboard..but since PEX is 1/2 the high output baseboard won't help.

Sounds like all PEX that was ran is 1/2..and he wasn't sure if the correct PEX for heating was used since what I have is all clear PEX. I will definitely look into it next time I'm up there and verify if it's PEX-AL-PEX.

thoughts? I just want to make sure I make an educated decision on this and make sure I can discuss the issue with my builder.

Thank you

Jose
 
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Old 07-17-14, 03:10 PM
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water is leaving the boiler at 180F and coming back at 180F
I doubt that. It would mean that there is ZERO HEAT output into the home. There MUST be... HAS TO BE SOME differential!

1/2" PEX is not necessarily the problem. It could be PART of the problem but that in itself may not be ALL of the problem.

There's a whole lot of physics that I'm not going into at this time, but let's start by saying instead that you may need to lower your expectations a bit. Bringing an entire structure up from 40F to 70F is a gargantuan feat. You aren't just heating the air, you are heating everything inside the heated envelope of the home. I'm not at all surprised that it takes as long as you say it does.

It's an UNREALISTIC expectation that you'll be able to crank the heat and have the home warm up in an hour or two from 40 to 70.

BUT, there may be 'deficiencies' in any case. You need to analyze the heating SYSTEM as a whole, not just look at the tubing and proclaim that's the problem.

There may in fact be nothing at all wrong with the heating system!

The first thing to know is if there is enough baseboard installed to match the heat loss of the home.

Even if there is enough to MAINTAIN the heat, it doesn't mean that there is enough to RECOVER the temperature of the building in a short amount of time.

How many feet of ELEMENT is installed in the baseboard cabinets? Just the ELEMENT itself, none of the bare connecting pipes.

Are all the baseboards connected in 'series' ? In other words, out of the boiler, into the first base, out of that into the second, etc, etc... describe how the system is piped.

If you don't have enough baseboard, you can have a NUKE PLANT in the backyard and the heating will still not respond as quickly as you would like.

By the way, the tubing does not need to be PEX-AL-PEX, there are other types of PEX that are suitable for heating system use. The tubing MUST have an OXYGEN BARRIER, that's the important point. When you get up there, take a close look at the tubing and tell us everything that's printed on it.
 
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Old 07-17-14, 03:28 PM
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you are correct we get some heat upstairs but not much, heating guy confirmed boiler shuts off. Good point about not having enough baseboard, heating guy determined that what I have isn't enough.

That's the reason they decided to look into replacing some of the baseboards with bigger + high output units and that's when they noticed the 1/2 PEX to baseboards.

I will find out more about the system itself and reply later on.

I appreciate your feedback, Thank You
 
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Old 07-17-14, 03:28 PM
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A bit more... because I'm not sure I explained myself well. Albert might be frowning at me.

Any given building has a certain rate of heat loss at a given temperature difference between indoor and outdoor.

Let's say that your home has a heat loss of 25 BTU per square foot (this is a hypothetical number used for example only. Your home may need more or less, but the principle is what needs to be understood.) when the outdoor is 0F and the indoor is 70F.

This means that for your 800 sq ft home, you need a heating system that can deliver 20,000 BTUH in order to MAINTAIN the temperature.

Your boiler would need to be able to output that amount, your piping would need to deliver that amount to your baseboards, and you must have enough installed baseboard to move those BTUs out of the water and into the living space.

This will MAINTAIN the temperature.

When you try to RAISE the temperature, you need to be able to move MORE BTU more quickly into the building.

Auto analogy time...

Driving down the interstate in your Yugo. You're doing just fine motoring along at 70 MPH (can a Yugo even make 70?) with no problem maintaining speed. It DID take a long time to get to 70, but you got there.

Up ahead there's a semi truck... you pull out to pass... mash the pedal down... your little Yugo tries to accelerate but is having a helluva time of it. EVENTUALLY, a few hours later, you manage to build enough speed to pass that semi.

You trade the Yugo in for a Chevelle SS396... power to spare... no problem passing that semi now... or three... or four... and you can get to 70 in about 5 seconds.

See where I'm going with this analogy?

Heating systems are designed to MAINTAIN temperature. They want to run in 'cruise control'. Designing a system that was able to heat a home from 40 to 70 in an hour or two would be a HUGE WASTE of money and fuel! Like the difference between 20 MPG in the Yugo and 8 MPG in the Chevelle.

Before spending a lot of money, you need to be sure that your system isn't doing exactly what it's supposed to, or designed to.
 

Last edited by NJT; 07-17-14 at 03:50 PM.
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Old 07-17-14, 03:39 PM
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Is there an outdoor reset on the boiler?
 
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Old 07-17-14, 03:53 PM
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Good point about the OD reset...

But most these days have a 'boost' function that bumps up the water temp after a certain time of not satisfying the heat call...

... and it was stated that 180 F water was flowing.
 
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Old 07-17-14, 04:01 PM
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You're right. When I put an outdoor reset in this is the call I get almost every time. I don't think pipe size has anything to do with it. If anything the high limit on the aquastat might be off. I've seen it happen. I would make sure the zones are all purged and that the valves are all open all the way. The circulator might not be working too. When it's calling for heat feel the body of the circ to see if it's actually running. Make sure the arrow on the circ and the arrow on the flow check are pointing in the right direction.
 
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Old 07-19-14, 01:30 PM
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I traced the piping between boiler and baseboards..

let me know what you guys think...not sure what's up with those 1/2 fitting connecting 1/2 PEX on both sides.

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Old 07-19-14, 05:19 PM
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Maybe you missed this in my earlier post?

By the way, the tubing does not need to be PEX-AL-PEX, there are other types of PEX that are suitable for heating system use. The tubing MUST have an OXYGEN BARRIER, that's the important point. When you get up there, take a close look at the tubing and tell us everything that's printed on it.
Were you able to determine if they at least used the right stuff?

It looks like you wrote " 1/5 " instead of 1/2 ... you meant 1/2 I'm sure.

The 1/2" tubing is not really an issue. 1/2" is capable of carrying about 15K BTUH (in copper, PEX is slightly smaller inner diameter, so a little less... let's say 12K BTUH). You have about 12K BTUH on the longer of the two loops, so the 1/2" is not the 'limiting factor'.

You've got about 20K BTUH of heat emitters (baseboard) installed and you said this was new construction? So one would think that the insulation and whatnot is all up to modern standards.

800 square feet at 25 BTUH / sq ft is 20K BTUH so that all seems OK.

Your system wasn't designed to pass 3 semi trucks in a row. It's designed to maintain the heat at a 'set level'. I really think that your expectations are a bit high thinking that you should be able to come from 40 to 70 in a couple hours. Ain't gonna happen.
 
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Old 07-20-14, 06:46 AM
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Is that stuff really PEX tubing? From the photo, it looks more like rubber hose connected with hose clamps.
 
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Old 07-20-14, 07:44 AM
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Looks like crimp rings to me...

If all the holes that tubing goes through are as tight as that one appears to be, it's gonna be noisy. PEX needs room to move.
 
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Old 07-21-14, 12:13 AM
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Get a furnace. Maybe two... one for thermo-blasting the place for a ridiculously fast heat up (I can almost hear the pings and odd sounds), the other based on a very very light heat load (since it has a huge big brother).

That short piece of tubing, less than a foot, before a coupling fitting (unneeded expense, failure point and a significant bump in pumping head on that branch), says way too much about the rest of the system. Never mind it doesn't quite match the other piece. Perhaps a bit too much UV exposure? Not good...

I love hydronic heating but for a cottage that needs fast recovery and might freeze... furnaces do have their place in the heating world. If you stay hydronic consider oversized panels (especially in key occupancy space) with TRVs and repipe it all properly - reverse return in your case. There shouldn't be any intermediate "connectors" with pex piping. Manifold > Panel > Manifold. You don't want a fitting and a leak happening in enclosed space.
 
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Old 07-21-14, 08:42 AM
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Based on the location of the two coupling fittings, I'm gonna hazard a guess that when they were piping it up, they 'forgot' about that basement baseboard... and spliced it in afterward.
 
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