New Boiler/Size & Pipework

Patrick1

Hello everyone,

i have to get a new boiler, current boiler (damaged) is an HTP Elite 301. It’s a 299 Btu i believe. Water tubed high efficiency.
It has to be replaced.

We are looking at a 199btu Bradford White and are unsure if its powerful enough since the old boiler is 300k.

House is almost 4000 sq *edit *(5300)foot 3 story Colonial Garrison with a basement.
The plumbing on the hot water boiler pipes are original early 1900’s. Has many cast iron radiators and a couple baseboards. People think it used to be a steam system. But i don’t know because all the radiators have been replaced or messed with so some i can tell are from steam systems some not and i dont know which ones are the originals.

Measuring out the radiators and baseboard i am calculating i need about 165k btu. 175k btu if i replace 2 short baseboards back to a cast iron radiator.

Many suggest Bosch, lochvar, Bradford, etc.

Many also suggest 2 smaller boilers instead of 1 big commerical size boiler etc.

Why was a 300k btu boiler installed in the first place and is that even needed?

Im looking at a firetube instead of a water tube. One tech advised a firetube high mass boiler… but the ones im looking at i assume are low mass boilers.

is there any benefit of using a firetube with a cast iron system instead of a water tube.
Will a firetube be inefficient?

Another issue i am wondering is the plumbing going to and from the boiler.

The current circulation pumps i wonder why they were installed this way.
is it okay to have the pumps before the pressure tank?

I know that the system is unbalanced because some radiators have alot more pressure then others when the system is hot.

I have also been trying to get all the air out of the system and proper psi.
When the system reaches temp the 15 psi rises to about 20 psi or more when the boiler was shutting off. Is that normal or okay?

There is 3 lines with isolation valves coming off the primary for the return.

hvac guy would like to install a loop with a circulation pump off the send to help add warm water into the boiler as to not shock it. That may be all. Mentioned about completing the primary but i don’t know what or if that would be altered.

A different hvac guy suggested something that sounded like cutting everything off at the primary and installing a new secondary loop, reinstalling feeder, adding a 2” header and adding a low temp sensor on the return to keep boiler water above 130 degrees.

hot_rod

a boiler like that should be piped primary secondary. It looks like the used high head circs to overcome the pressure drop. The y strainer on old pipe systems should be checked yearly, use a separator instead on the new piping.

Two boilers give you twice the turn down, so 20-1. Also redundancy.

I would suggest a hydraulic sep in an old iron pipe system. Air, dirt, mag, and hydraulic separation would protect the boiler and pumps.

Patrick1

So what you are saying i have not a complete primary? Because there is a large primary that everything T off of but returns with its own run.

I had no idea that was a Y screen.
yes on the new installation we are talking about adding a new screen.

So everyone wants to do Copper, i personally want iron because i dont like to mix metals for multiple reasons. But would copper be surly okay? Im mainly wondering about heat loss from a copper run.

also that bottom pipe along the trap door is a return from other heaters, its hard to tell from the picture with the angle.

hot_rod

here are piping options that are generally in the installation manual for high efficiency mod con boilers

IMG_0862.jpeg

EBEBRATT-Ed

Copper is fine mixed with black pipe. No issues on a closed loop system.

Jamie Hall

Ah… before you do anything, someone needs to do a heat loss calculation on the structure. Otherwise, you have — quite literally — no clue what size boiler to install.

The old one may or may not be the right size. I may be much too big. It's unlikely it was too small…

Then, and only then, can you start worrying about which boiler and how it might be piped.

Patrick1

not really to sure how to do a heat loss calculation.

hot_rod

if I were a betting man I would guess a load of around 100- 120,000

4000 sq ft x 25 btu/ sq ft 100,000 btu/hr

So a 150,000 mod con boiler may be adequate

Look at @RenovationWontEnd post in Radiant Heating, he just did a heatloss with a spread sheet

Patrick1

i had a typo its more of 5300 sq feet

Patrick1

The expansion tank is for 12 psi, the auto feeder may be broken so i have been manual feeding it when i need to. Which blocks off the air trap….I had to work on a couple radiators earlier this year and drain. So it seems to need around 15 psi to get the radiators on the top floor to bleed. On first call for heat the pressure gauge in return when the circulation runs drops to around 5-10 psi then as the system heats it slowly creeps its way up to around 15-18 psi. And the top floor radiator starts to get hot Then if i shut the boiler down it instantly spikes to around 20 psi or more.

is this normal? Its been tricky because I don’t want to over pressurize any part in the system. I imagine there was just an airlock in there somewhere

after the water gets up to higher temp the HTP was reducing the fire rate to keep the water maintained. I cant remember at what percent maybe around 70% and i want to say set point was 180 but water temp seemed to be struggling to get above 165 for supply like it was maxing out almost.

If the 300k btu boiler still modulates down to a lower fire rate when reaching optimal temp wouldnt that be a good sign its the right size? Also the outdoor temp sensor was disconnected.

1 of the installers recommended not installing the outdoor temp sensor that they are unreliable and not needed. Also stated i dont really have a primary or secondary and should have a primary configured. And that a low temp sensor on a return isnt needed.

1 installer recommended installing an outdoor temp sensor and then installing a low temp sensor on the return to keep boiler water continuously circulating on a primary at no less then 130 degrees to boiler health. And that a secondary loop needs constructed to maintain that.

But niether were aware that these boilers they recommended were FIRETUBE designs which tells me they assumed they were water tubed.

Patrick1

i keep calculating anywhere from 50-75kbtu/h heat loss. Does that sound normal or is my math wrong? Thats not really taking into account the refrigerated third floor walls from the balloon frame.

This is for a 3 story Colonial Garrison, uninsulated, gabled roof. With a basement 1/2 below grade

What im not understanding is the concept of calculating heat loss. I have X amount of cast iron radiators that could potentially put out X amount of BTU. If i have 175btu or radiant heat wouldn’t i want at least 175k btu of power and a little extra?

hot_rod

it is possible if there have been upgrades to the building that it has more radiator capacity than you need. That would be a good thing as you could run at a lower boiler temperature.

You could calculate all the radiator output and match the boiler to that.

Better to know the actual heat load as it stands today. A wild approx but 20- 25 btu/ sq ft is not unreasonable 5300x 25 btu is 132,500btu/hr. 1/2 the size of the current boiler

Patrick1

yes there has been a couple radiators replaced with larger ones, replaced with fin tube, and possibly 1 added. But for the most part its the same. The house was built in 1913-1925. Everyone in this part of the city ran coal. Alot of people here still have the original coal boilers and use them!

ill have to calculate the radiator output again but the last time i got 165k btu. And if i reinstall 2 more radiators on the 3rd floor to the original pipes that makes it over 175k btu total.

I think that 150k btu boiler would be to small.

On a setback it takes the 300k btu about 45 minutes to reach temperature from room temp water. And the radiator on the 3rd floor is the last to start warming up and then the whole system shuts down not heating the floor. The only control is the thermostat in the center of the house.

hot_rod

A big difference between "thinking" and calculating :)

175,000 divided by 5300 square feet is 33 btu/ sq ft. That is a pretty big number, unless some windows are missing?

A few hours, to do a load calc, or send the house plan off to have a load calc done. Maybe have a heat and cooling load calc done, if AC an option.

With a lot mass, in the radiators and the volume of water, setback might not be a good idea. It's like getting a long freight train up to speed.

An outdoor reset control to modulate water supply temperature and keep water flow constantly is a much better control strategy. Put heat energy into the building at the rate it is loosing heat is ideal.

Patrick1

when calculating btu output of cast iron radiators should i use the old standard of 240 BTU or the new standard of 130 for an old house old engineering

LRCCBJ

The standard of 240 BTU/square foot of radiation has not changed. Steam at 212F is a constant. So is the 240 value.

There is no "NEW" standard.

Patrick1

Oh okay i wasn't sure. the engineering standard from the american radiator company lists 240 btu. I thought that has since changed to 130 btu standard.

This catalog is from 1937 but I imagine wasn’t much different from 1913-1925

This is all a new area of study for me

https://heatinghelp.com/assets/documents/American-Radiators.pdf

Patrick1

is it typical to oversize with a safety margin of for example 1.2?

Patrick1

for the bradford white brute it says not to install on a primary secondary?

Page 43

https://bradfordwhitecorp.s3.amazonaws.com/wp-content/uploads/residential_boiler_floor_standing_brute_ft_bfthf_iomanual_1510.pdf

GGross

https://forum.heatinghelp.com/discussion/comment/1826004#Comment_1826004

Looks like that boiler has a built in low loss header and pump, so your boiler loop is all internal and then you direct pipe to the system, primary/secondary is built in by default.

Patrick1

would that be better for my system?

The other boiler im looking at is

https://www.lochinvar.com/lit/KHB-I-O_Rev_M_100305277_2000558126_%2860752%29.pdf