Navien combi will not heat house above 68, ran constantly from November to April

Rich_49

Guys , this is a hell of a case study .
What we know .
Old cast iron boiler heated house to 72* handily .
New Navien combi does not .

Older house , Block walls , no siding (painted) . 1" firring strips with sheetrock attached interior .

Ventilated attic with duct work for A/C , Insulation that is there may be considered R-2 .

Ventilated crawl , R 13 value after deducting for thermal bridging downward . One pipe system , 1 1/4 with bow tie looking tees . 3-4 pieces of heat removed from one pipe and capped as opposed to connected . Baseboard is Koven cast iron with a steel jacket , random piece of SF here and there . Some of the baseboard is returned within the cabinet and it is reported that air has been a constant issue since replacement of CI boiler . Not surprised by this . ENTIRE perimeter of home has baseboard save for a couple feet in closets . One pipe loop is >=200' and some of the sections of heat exceed 80' TDL . There is a bit of added head loss throughout by the way of some 1/2" fittings and pipe .

Circ is B & G NRF 22 , the old circ was 007 . basically same . No effective air elimination as can be seen in the photos . Delta is right around 20* (19-21) as witnessed on the system loop . baseboard did not start to heat up until what I believe was thermal migration from the loop in crawl .

There is wall to wall carpeting in the house that does not allow any convection to really take place . The installing contractor who had the exhaust backpitched at one point , shut down on pressure , had to pipe this thing in 4 incarnations , did not perform any type of heat loss , did not survey the system and house to see what he was dealing with , is pointing at the lack of convective ability as the source of the problem . he had free reign to spec anything he wanted , the homeowner just wanted a good modern heating system with new equipment so he would have one less worry as he grows older . REMEMBER , the house heated to 72* before the change .

My thought is the old boiler was set at a very high temp and worked despite the issues throughout the home and system . It does not heat the home now . Please refrain from mentioning that 728 is a high ambient temp , that is what was specified to design for , and just like naked people , the elderly and aging in place deserve comfort also as they advance .

I may have missed one or two points and am open for questions . Was this the proper piece of equipment to specify taking into consideration that the problems that existed in other areas were not to be addressed ? The homeowner is also available for questions .

njtommy

Wow did I read that right almost 100k heat loss in a 1400 sqft house?

I'm not surprised about the hacked up mono flow system.

Paul48

I can't tell you how many times, people have come here and have replaced a series 100 with a 007 on a monoflo system, and it doesn't work. I bet it had a series 100 originally. Just thinking out loud.

Rich_49

But the 007 worked in the cast iron boiler configuration Paul . There is just no proper air elimination to speak of .


Tommy , that would be correct . Please keep i mind though that it is a bit exaggerated due to the 72* indoor temp and a 5* ODT . This one is being designed for the occupants as opposed to the building . Bill requires slightly elevated indoor temps for his comfort

Hat ,

The boiler is lacking in **** if it could operate at it's rated efficiency . Since we require high temp , it will probably never see an AFUE above 85% . Well now that leaves us about 12,000 short at design . I will be discussing a stepped plan to rectify as many issues as possible , picking at the low hanging fruit first . This will be a progressive job I have a feeling . I do want to change from a one pipe system to 2 pipe Reverse return . It would serve this particular house much better than what is there .

4Johnpipe

Aside from the results of the heat loss. The install is lacking proper hydraulic separation. We are registering higher boiler return temps due the secondary piping being equall size of the boiler supply and return. Instead of hea transfer at a separator we are getting heat return to the boiler. Simple physics the water is lazy and will more readily return to the boiler instead of mixing at the point of counter flow. High pressure will go to low pressure any day of the year...

Paul48

Don't you have to get the secondary side pumping before making that determination? Out of all that mess in the pictures, it did appear that he had P/S piping with closely spaced tees.

4Johnpipe

There is flow in the secondary...just not making it out to the emitters in all areas or if it is its not carrying the required BTU's...The secondary return seems to be traveling up to the boiler return as apposed to exchanging its heat in the primary secondary connection point...We definitely do not have adequate hydraulic separation going on...Stay tuned...

RobG

Are you sure the home has no insulation? Many of the block homes in my area have Perlite filled in the block cavities. I always drill a hole to see if it's inside.

Rich_49

Rob ,

Homeowner's father in law built this house and he has listened to the war stories for several decades . A group of longshoremen built this place so my bet would be beer cans crushed in the walls . Keep in mind this is a resort town and when built this was a summer retreat .

Taking into account the Perlite really is not much of an R upgrade due to thermal bridging of the webs . Hell , a modern house with R 19 walls while having the R 19 center cavity value the assembly is only about 13 .

RobG

If the guy knows how it was built that says it all. I'd still rather have Perlite filled walls than nothing at all though. 97K btu's for 1400 square feet is amazing! His best investment would be insulating, air sealing and storm windows. At that point the boiler would probably keep up.

Rich_49

I don't disagree Rob . However , we are where we are and those options are not on the table . Would you care to opin on whether a heat load calc should have been performed , a survey of what was existing conducted before this contractor sold this unit to this consumer whilst not knowing how to install and pipe same ?

RobG

I shall opine and yes, a proper heatloss and system evaluation should have been done and in a perfect world the contractor should be standing behind his work and making the system right. Alas, we don't live in a perfect world . I do however think that before throwing the baby out with the bathwater, insulation, windows and envelope upgrades should be considered to see if the unit he has already paid for can handle the load (with piping corrections). JMHO