long time lurker first time poster new RFH & Combi install woes

Ya2UP_A · November 2022

After recently purchasing quite a rehab home against any wish or desire, (another story for another forum), in a semi remote (in comparison to anywhere else we’ve lived over my 20+ year military career) “I’m in the process of quite the DIY heat conundrum, I’m needing some help with to verify its correct or not however either way its challenging getting contractor work to show up and on budget in this location, so here goes.

Home had a Burnham oil fired boiler which hadn’t been fired in what looked to be over a decade, its primary heat source was a patch work welded Johnson out door wood boiler tied in with a external plate heat exchanger with an indirect DHW for the heating season and also for the off season had an old dormant electric direct water heater plumbed in as well as a newer’ish direct LP water heater that was in play when purchased during the summer months.

I’ve since removed all this and replaced with a propane wall hung Rheem Prestige 9.9 Combi unit, old system was base board radiators, also removed and replaced with 2,500’ of ½” Pex staple up for radiant floor heat, with a single zone 8 circuit manifold which was working ok until the cold came, I’m getting a constant 130 degree supply at the manifold going out but cant get over 70 degree at the return side of the manifold, just to test I cranked it up to 150 for a short period and still can’t overcome 70 return.

I have an average Delta T of 60-70 degrees! Granted the joist bays are not yet insulated and won’t be until this coming weekend (maybe) the system is piped in a primary/secondary loop fashion with a Taco 007 pushing supply into the manifold through a 3-way mixing valve.

My concerns and observations thus far are: the supply/return close spaced T’s coming out of the unit are at 5.5 inches apart, I believe they should be no more than 4 with 1” copper to the manifold, also have two 45 degree lbs well under 4 inches from said T’s, so even with a 60 degree Delta at the manifold the supply and return 1” copper at the unit both feel about the same 130 degree is this correct?

Second I strongly believe there’s way to much head for that 007 to keep up with, I’ve done the math multiple times however I’m no math statistician nor boiler surgeon, so I get different results every time, but in layman’s terms the side of the house nearest the boiler maintains the 70 degrees set temp whilst the farther side isn’t getting any love at all, so doing a one by one visual check and flow test on each circuit there isn’t much flow on the far end circuits, and lastly the mixing valve which was piped in after the Taco 007 I’m reading conflicting info on what side of a circ pump the mixing valve should be on, in this config there is no room for it before the pump oh and the reason for said mx valve is in future plans there will be fin tube base boards again in the not now but future finished basement.

My thoughts to overcome this huge Delta T and get proper heat and stop hemorrhaging propane is: 1. I’ve ordered a Taco VT2218 to replace the 007, 2. maybe disassembling the loop and trying to move the primary/secondary close space T’s within 4” or less while adding some copper between them and the 45 coming out of the unit, (although I hate to bring down and drain while were in the teens and dropping fast and lastly and most obviously insulating the Pex.

I can provide Pics if needed, also need to point out there was very little space to work with here, all this is on a 4x4 sheet of plywood on the wall so there’s a lot going on in such a small space. Thank you all for any help and assistance with this!

Jamie Hall · November 2022

Do you have some way of checking -- or better yet, balancing, the flow between the various loops of your radiant system? And can you draw a sketch of how the thing is piped? Remember that the secondary pump which pumps into the manifold for the loops has to be after the mixing valve, the cold feed side of which pulls from the combined returns and the hot side of which pulls from the upstream one of your closely spaced Ts. Then the remaining return flow goes into the downstream one of the closely spaced Ts on the primary (boiler) loop.

Ya2UP_A · November 2022

Thanks for the reply. Yes, I do have flow regulators and

meters on each circuit that were provided on the prefabbed stainless steel manifold, I have been experimenting with the flow rates trying to balance since yesterday, cant really see a diff yet other than those rooms/circuits closest to the boiler not getting as hot however its not doing anything for the further circuits. I have attached a simplified sketch to get a better idea as well as pics of the real deal which is kind of hard to see what's going on. What is the ramification of having the pump on the wrong side of the mixing valve?

hot_rod · November 2022

Is it all radiant now? Why a mixing Valve? Cant you just run the boiler at the temperature the radiant needs? Even better yet on ODR?

If for some reason you need a mix valve, you need to pump out of the MIX port, not into the H port.b

Ya2UP_A · November 2022

It is all radiant now, the mx valve was because in the near future, I had planned on adding fin tube style radiators in the basement, figured there gonna need much hotter water than the pex, thought process was to mix down the 180 just before the pex manifold, when researching this build, I saw several of the prefabricated big box store radiant panels built that way. with that said I do have that mixing valve currently cranked wide open.

hot_rod · November 2022

A slight modification as shown will work.

Remove that pump from where it is, add a spacer if you don't want to remove the flanges, or solder a pipe in there.

Leave the two future tees and ball valves where they are for future high temperature, it will need a circ when you get to that.

Next connect the 3 way as shown here, use the Taco you have on the mix port of that 3 way.

With a 3 way valve the pump pulls from both H and C port, it will not mix properly pushing into the H port as it looks like you have it piped. But I guess you discovered that already

There are some brands of 3 way valves with different port configurations, yours looks like a common T pattern, mix out the bottom. The ports should be labeled. H, C and Mix, sometimes A, B and AB.
The Menard panels may use a different type of 3 way mix valve.

Know also the hot supply to the mix valve needs to be 20- 25 degrees hotter than the mix you are targeting. If you want 120 to the radiant, the boiler needs to be 140F. All thermostatic valves work that way. TGheyy need a temperature differance to be able to adjust and mix.

You might be able to "cheat" your way out of a repipe by removing the guts from that mix valve, that usually allows full hot from the boiler to go to the manifold. Adjust the boiler temperature accordingly. balance some temperature with the valves on the manifold.

Until you add the high temperature zone, may as well run the boiler temperature as low as possible to drive efficiency up. So direct to the radiant with no mix valve.

Ya2UP_A · November 2022

Thanks for the clarification, If I bring it down and some how reconfigure that MX valve in front of the circ pump like it should be, will that correct my wide differential I currently have which is between 150 and 70? or do you think that goes back to the head pressure and insulation? again I don't have a whole lot of room for piping, cant see in the pics but that board is sandwiched between the old indirect DWH and the sump.

Ya2UP_A · November 2022

I apologize looks like you typed a help response as I was still typing thanks so much for the advice! I'll give it a shot tomorrow

Ya2UP_A · November 2022

I do have a follow up concern before applying this fix, if you look at the supply side pex manifold its reading 150 degrees, so essentially the system is getting all the hot water I'm sending through that mx valve, its the return I'm more concerned about, the C port on the Mx valve is actually cold (70 degrees) all the way down to just before the T going back into the boiler however, the main return on the boiler itself is just as hot as the supply? is that normal, or will this regulate and correct after I correct that mx valve position? thanks again!

hot_rod · November 2022

As you sure that you are not air bound and not circulating at all. That 70 you see could be just from the valve getting warm from the 150 side. Are all the flowmeters on the manifold showing flow?

Sometimes you can close off that red handle on the supply manifold, see if the flow meters move as you open it. You will hear fluid moving as you slowly crack open that valve. With the pump running of course

Many mix valves "fail" cold when inadequate flow on H or C side, so no mixing happens. Thermostatic mixers also need to be in a close pressure range. If pressure is higher on one side compared to the other the valve fails cold. I suspect pumping into the H port may be causing that condition.

If it arrives at the manifold at 150 and returns back to the boiler only a few degrees cooler, then you are not mixing, just going around a circle. Does the boiler run short cycle? That another indication that no heat energy is transferring into the loops.

With the isolation valves you have, it may be a 5 minute job to pull the guts out of the valve and see what happens. What do you have to lose?
You may find the cartridge inside is stuck not allowing any mix. Doesn't look like you soldered against the valve, that will damage the plastic inside.

The internals are spring loaded, so be careful when you remove the top.

Ya2UP_A · November 2022

Well, the flow meters are rendered useless as I mounted the manifold upside down as My pex runs go up to the floor joists and didn't have the room to create the under loops, I've researched this method and it seems many do this with staple up, just need to put the air seps back on the right way up. I have tested the flow several ways 1. by shutting the blue isolation valve and yes the temp shot from 70 to over 100 pretty quick and I could here the water turbulence pretty clearly 2. by opening up the bleed valve at the right end of the return while pump was on and I did get a strong discharge, I then I completely closed off each individual circuit on the manifold and opened one at a time with the bleed valve open and watched it pump out, doing this the farthest circuits had a week flow while the closer ones flowed strong, which led me to believe I may need a bigger pump, using Tacos pump selection and formulas I'm guessing I'm at 9 gpm but well over 12 feet of head, the 007 is only rated for 10 feet per there graph? I am most certainly going to gut that mixer, you are right I have nothing to lose at this point, will I have to bring down and drain the system to do this? I will admit although I can hear the flow turbulence when I close the manifold I did in fact repurpose this taco from the old system, so I cannot vouch for it, also why I don't feel bad ordering new one

hot_rod · November 2022

Those flowmeters are usually spring activated, they should move and read even upside down. Isn't this end one showing flow? Turn the main red or blue valve off and on, do the meters move?

That circ should be plenty if those 8 loops are between 250-= 300'. (2500' total?)
Typically 1/2 gpm per loop, so you would need 4 gpm for 8 loops.

300' of 1/2" pex at .5 gpm flow is just under 3' head. Throw in another 2' for piping and valves, so more like 5-6' of head, at 4 gpm. Well within that circulators range.

But the circ also needs to overcome that mixing valve. IF it is installed pumping into the hot, I'm not sure what the pressure drop could be. I suspect it is a 3 cv in normal configuration, so with 4 gpm required it should all work with that circ.

Shut off the red and blue manifold valves and you will not need to refill and purge. You'll lose some water between the manifold and boiler

Ya2UP_A · November 2022

Forgot to answe your first question, yes it is short cycling. Ok, I tried the flow meters. Turned off red and only two flowmeters moved slightly, all of them are sitting at 0, that’s why I thought they were in-op upside down. Yes I’m pumping hot into the hot port on mixer, cold is T’d into the return and mix is going to the red manifold supply. Good to know on the pump. I tried 3 different formulas to figure my head and got something different each time so wasn’t that confident in my ability doing it. Yes All 8 circuits are at or around 300’. I believe I will install the new adjustable speed pump closer to the manifold as you suggested and on the other side of the mixer when it arrives and pull the 007 and save it for the high temp side. I will be gutting the mixer first thing in the am, after I get the wood stove ripping that is! don’t want to chance having no heat at this hour. I will let you know how the mixer mod works for sure!

psb75 · November 2022

An "elephant in the room" is NO insulation under the tubing! Also, is the tubing put up with any kind of conducting material i.e. extruded aluminum plates (best) or thinner aluminum material? If not any of the aforementioned then a lot of the radiant heat is going to the cellar.

Ya2UP_A · November 2022

ok hot_rod I pulled out the cartridge this morning, wanted to wait a few hours to monitor before coming back, there is no change in the return temp, the supply did go up 10 degrees but Im still locked at 70 degree return instantly. I've filled and purged, purged and purged again, not sure if this would be an indicator but when I open the purge valve on the manifold red or blue I've done both, the return temp spikes instantly to match that of the supply? Then upon closing the purge valve it drops right back down to 70?
psb75, there are 3 1/2" by 48" aluminum plates every other 48" inches, yup I'm aware that at least 50% of my energy is being lost to the basement as there's nothing to stop it yet, really don't want to close in the joists until I'm confident with this this set up, plus its not all bad as the basement is being converted to living space. however, I really don't think that's what causing the extreme delta t I'm convinced this is a flow/mix issue, I'm not expecting contractor grade efficiency in this phase of the build but a 70 degree differential I believe is a problem indicator with or or without insulation.

hot_rod · November 2022

The single drawing is what I think is going on.
Flow from the loop is going across the valve up to that tee, and back to the boiler. Since that is the least resistance path, no reason for water to go to the loops.

Either pipe the 3 way correctly or..

Is the pump still down low by the boiler?

If you are up for another hack

. Cut a flat disc 1-1/4" in diameter. An old inner tube, rubber gasket material, even a piece of a plastic milk jug will work. Something stiff and waterproof, not cardboard. Loosen the nut on the top of the 3 way and slip that disc in. Plug off that top port.

So now flow comes up, it can't cross the 3 way. It makes a left turn in the 3 way valve and up to the top supply manifold.
Return comes back from lower manifold goes out the branch of the tee, back down the loop to get boiler temperature.

You have turned the 3 way valve into an elbow essentially. You will need to turn down boiler temperature I suspect you will get close to boiler output temperature to supply manifold this way.

Or completely redo the piping as drawing 3 shows, when you want the high temperature zone, the piping needs to be redone however.

hot_rod · November 2022

Also, the white caps on the manifold, are they screwed down all the way? Those are shutoff valves if the cap is off or backed open all the way. Turn the small part clockwise all the way down.

Ya2UP_A · November 2022

Joys of satellite internet had a bit of a storm yesterday so no connection. Outstanding idea as yes, the pump is still in its original config, I’m not gonna be able to cut and repipe until this holiday weekend but will try blocking that return branch in the mean time as that makes sense and as you’ve said what do I have to lose. The white caps, yes there full open I’ve played with these quite a bit.

Ya2UP_A · November 2022

Oh I just caught what you said on the caps. So you’re saying tighten them down clockwise, ok I’ve done this and thought that was closing the loops flow. Yes when tightened all the way down the return temp at the manifold is within 20 degrees of supply but I thought that’s because the supply was dead heading at the manifold vs flowing through the circuits. Let me go crank them down and let it sit for a while.

Ya2UP_A · November 2022

Drawing 1. Would make sense with this configuration however, if that’s what was happening wouldn’t that return loop “stealing the supply” be hot as well? Because it’s not it’s room temp as well.

hot_rod · November 2022

The flow will take the path of least difference, always. So I suspect the flow would want to go across the valve, right back to the boiler.

Perhaps if the flow had to turn in the 3 way body, it would blend a bit. Too many unknowns in this piping.
I do know when piped correctly they work great

I'm just trying to come up with options, instead of a complete repipe. At least until you add you high temperature zone.

The 007 is flowing the right direction? It is not seized up and not pumping any flow? Usually if they get real hot it indicates it is jammed.

The disc is the next easiest workaround.

Adk1guy · November 2022

Friends check me if I am seeing this correctly. The only thing I see pushing water into the heating loops is the resistance of the mixing valve.
Hopefully there is a circulator inside the boiler to push water around the primary loop. If not you need one. Your set up needs 2 circulators, a primary and secondary. I would cut out the mixing valve and run directly from the secondary circulator to your supply, then from return back to the primary look. Your secondary will 100% flow through the heating loops. It will still be a loop but all the water would pass through the radiant tubing to get back to the primary loop.
It looks like you have 3/4" pipe but that is only good for 40,000 btu on standard btu per pipe size charts. Check your manual to for the specified primary loop size.
I would also look at sizing your future panel radiators using the same design temperatures as your radiant. Mixing valves need a delta 20 minimum and are restrictive. More and/or larger radiators and a lower system temperature equate to heat coming from everywhere, fewer drafts, increased efficiency.

Ya2UP_A · November 2022

@ hot-rod. So I believe cranking down the white caps maybe closing off the circuit flow here’s why I think that. After cranking down clockwise, that return pipe coming out of the mixer now heats up so now it’s in fact bypassing the manifold and going right back to the boiler. To further test this. I closed the blue isolation valve in the Manifold and then Open the purge valve and nothing flows. I then, with the purge valve still open and the iso valve still closed turn the with cap back counter clockwise and I’ll then get flow out of the purge valve. I do this one by one one at a time to verify each loop is flowing. The farthest loop just trickles while the closest had a steady flow (I will retrace that loop for any kinks, twists for obvious no no’s hence why I haven't insulated them in yet). I followed the flow arrows on the taco flange so I believe it to be correct, don’t think it’s Locked or I wouldn't get the test results stated above?

@ adk1guy there is an internal circ pump in the boiler, it pretty much stays constant on then when the call for heat comes in the taco will kick in, which is used to push water into the pex manifold however, I now know the mix valve is on the wrong side of the pump. This all 1” Copper with exception of the darn mixing valve which is necked to 3/4” it’s what they had in the shelf at the local Ace, I should have ordered a 1” 🤦‍♂️.

The only way I was aware of to mix the two delivery system pex and tubes was via a mix valve as I understood pex should be around 100-120 max while those fin tubes require a min of 180. Any other way is beyond my knowledge level. At this point I would scrap the mixer and go straight to the manifold however, in about 2 months I will be framing and insulating this basement to create more living space for us, and will be well into the single to - digit temps then.

hot_rod · November 2022

You are correct about the caps, sorry about the confusion. Most brands of mixer have the same flow Cv in 3/4 and 1" so that is not an issue. Eight loops at 1/2 gpm per loop= 4, no problem for that mix valve.

Did you try the disc/ plug? It is a temporary fix. Once you need the two temperature system you need to repipe the mix valve.

You need two pumps, for high temp, one for radiant low temp. Plus one in the boiler.

Two things to check. Supply out of the boiler is the left pipe as you look at it?

Confirm the ports on your 3 way thermostatic. Most are like what I show here. H and C across from one another Mix out the end opposite of the knob?

So as shown the low temperature pump pulls a blend of H and some from the return manifold. The valve makes that adjustment inside with the heat sensitive element. A portion returns back down to the boiler tees to be warmed.

Ya2UP_A · November 2022

Thanks hot-rod. Yes, supply out of the boiler is on the left. I haven't tried the plug yet, was going to right before the toilette came through the floor... to follow-up on your last yes that is how the mix valve is plumbed although now knowing incorrect but yes hot is "pushing" into the H port, C is drawing from the blue return manifold and T'd back to boiler main return and mix is shooting up to the supply red manifold. My concern with the plug is, is the supply manifold is in fact getting set temp water at 150 degree however that water temp coming through mixer that I would be blocking off is cold. So I don’t think the hot water is passing though there like the 1st drawing in last post as suspected, all return is cold untill it gets to the main supply from the boiler where it turns hot again which goes back to my original post question are the supply and return coming directly out of the boiler supposed to be just as hot or are my T’s there too far apart? Take a look at the attached drawing I broke down the water temps at what location with a red and blue marker and let me know what you think. Thanks again for any assistance and wisdom with this.

hot_rod · November 2022

With the plug in the C port hot goes to the manifold, cold return cannot go into the C port because of the plug, so it goes back to the boiler. With this piping you would need to turn the boiler temperature down to 120, there is no mixing going on in the valve

Ya2UP_A · November 2022

Good copy. I’ll give it a try when I get back home tomorrow evening and let you know. Thanks.

Ya2UP_A · November 2022

Weekend update: Never plugged the cold return on the mixing valve as hot-rod suggested last week, as I knew I was re piping this weekend anyway. So I removed and straight piped the original 007 circ location and installed a brand new VT2218 on the other side of the mixer as suggested. Brought everything back up and although not as drastic couldn’t overcome a 40 degree delta t, and now couldn’t get over 100 degree supply at the manifold no matter what the boiler set temp was, so brought it back down pulled out the mixing valve and applied hot-rods hack of plugging the the cold return (I used a nickel) I also noticed another plastic spring loaded cartridge in this port maybe check valve? So I gutted that as well as the main cartridge, put it all back together and brought it back up and it’s running perfect! 120 out 100 back! And all circuits are hot and flowing. Pump was certainly on the wrong side of the mixer (thanks hot-rod) I believe said mixer was bad as well, will replace with a new better quality one when the time for high temp is needed. Thanks everyone for your help, a lot was learned!

long time lurker first time poster new RFH & Combi install woes

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