Not enough pump? FHW in older home with multiple conversions over the years

sokoloff

Have a 1920s home in New England (brick, no insulation in most walls, insulation only in finished attic and one bedroom).

On days below about 20ºF, the system doesn't keep up with the building heat loss. We're going to replace the boiler at some point and I am more concerned with ensuring that is properly engineered than I am specifically concerned with improving the current system. (That said, I'm more than willing to spend money to accomplish either goal, though am much more willing to spend on informing future engineering than on band-aid fixing the current boiler.)

Background:
Heating system is an estimated 1950s GM cast iron oil boiler, converted in approx 1991 with a 200MBtu/hr natural gas conversion burner. Original piping appears to be for cast iron radiators [one convector] on the 1st and 2nd floor only and via gravity circulation, since converted with a B&G Series 100 pump for that zone ("zone 1"). A second attic [3rd floor] zone was added by a prior owner (probably at the same time). That is piped with 3/4" copper and is 9' of baseboard in a bathroom and 19' of baseboard in the attic room (Slant-Fin, looks like Fine/Line 30), with a Taco 007-F4 circulator.

Both circulator pumps pump into the boiler. Zone 1 is piped in two main branches and both are direct return (or whatever "not reverse return" would be called). System has no active air scoop or vent but is well bled (EDIT: system was not well bled; I ran another "what the hell can it hurt?" purge on the attic zone and as I was about to declare everything was fine, I got a couple of quite large burps of air out of it; that zone immediately had uncomfortably hot return water when I turned everything back on) and has an expansion tank [set at 16 psi, same as the fill valve]. Aquastat is set to 200ºF, though I bumped it to 210-215ºF this morning when I started looking more deeply into this problem.

We've been in the house 12.5 years now and the system is tolerable, but between the poor insulation and inefficient heat transfer, the comfort is not great.

At some point (possibly this coming summer), we're going to replace the boiler and do some amount of repiping down in the basement with the primary goal being increased comfort and a secondary goal of lowering the operating costs.

Primary Problem:
On cold days, the system doesn't keep up with the building heat loss. The boiler cycles readily and easily maintains/regains the setpoint, which suggests to me that there's a surplus of input energy available still.

The return water from both zones is low enough that I can very comfortably hold my hand on the return pipe while the supply pipes are both scalding. (I don't have a non-contact thermometer but will get one and provide numeric measurements.) On zone one, the nearest radiator to the boiler gets too hot to comfortably hold your hand on; the middle radiators are clearly on but you can easily keep your hand on them, and the farthest radiators are "well, you can tell the heat is on, but barely". On zone two (attic baseboard), the supply pipe is scalding hot in the basement and the attic, but the return pipe is warm at best in both the basement and attic.

Secondary Problem:
The heat is not very even in the best of times. The dining room (first radiator) is comfortable, while some of the bedrooms are cool and the very last room on the first floor is unusable (it also has a ton of glass and exterior walls, but the radiators there are barely warm).

On the primary problem, I am thinking that I may just not have enough pump on either zone or the boiler is presenting too much restriction to flow. When I do an equivalent feet calculation on zone 2, I get about 190' equivalent of 3/4" copper pipe, and 16K Btu/hr of radiation at (20ºF delta-T, 1 gpm). I'm seeing a whole lot more delta-T than 20º and so I'm wondering if I don't have enough pump; looking over the pump curves, I was considering replacing the 007 with a 008 (or 009 if that is more indicated).

On the primary problem with zone 1, I'm also wondering if I have far too little pump there as well or if the problem on that zone is more related to the direct return piping arrangement (which is almost certainly the secondary problem's root cause).

The house is livable (and this winter is no different than past winters comfort-wise), but I want to make sure that I gather any information that might inform our choices as to boiler or pump sizing or piping arrangement for the upcoming boiler replacement project. I had two contractors out last summer and gave them both my concerns and we walked around the house and basement. Both came back suggesting that the problem was not enough boiler (and/or not enough insulation), and quotes that included an even larger boiler, which didn't give me much confidence in their ability to do engineering. (I'm sure they'd be fine on the installation and mechanics, but I want a properly engineered system in addition to a good install.)

We plan to stay in the house for "the foreseeable future" [10+ years], hence the desire to engineer things correctly.

Thanks in advance for the advice.

(Edit to note the initial lack of bleeding. That addresses the most major issue that seemed like it was "new" with this cold snap. The remaining issues do remain, but are now probably much less severe.)

Zman

Running the boiler at 210-215 makes me a little nervous. I think keeping it under 195 would be a better plan.
Your high delta T on supply/return is an indication of too little flow. It also sounds like you have some balancing issues. I would start by drawing out the piping so you can better understand the required flow and system balancing. You may want to look into thermostatic radiator valves on the original gravity system. In the mean time you can experiment by partially closing the radiator valves that are getting too hot and seeing if the others improve.

Alan (California Radiant) Forbes

The first step is to get someone in there to do a room-by-room heat loss calculation. This will nail down how much heat each room will need on the average coldest day and will tell you if the existing radiators are too large or too small.

It will also tell you what size boiler you will need to heat the house. From what you say, your existing boiler sounds too large.

And it also sounds as though there's something up with your distribution system, perhaps too many radiators on a too small distribution pipe. Maybe even that direct return is a problem as well.

Tell us where you are in New England and maybe we can help find someone who can figure things out for you.

Jamie Hall

There are several factors playing off each other here, and to get the system really working well you need to balance them.

First thing to do is to figure out just how much heat each of your radiators or baseboards or convectors can put out and at what temperature water. Then figure out what each space needs in the way of heat (Slant/Fin has a nice calculator which will do that: https://www.slantfin.com/slantfin-heat-loss-calculator/) -- the combination of those two pieces of information will tell you what temperature you need to run the radiation at to be warm. Or at least warm enough.

The total, incidentally, will also tell you two other useful things. First, is the boiler actually the right size? That is, can it in fact deliver the amount of heat needed to heat the building? There's no point in going bigger on that. Second, do you in fact have enough installed radiation to do that at any sort of reasonable temperature, or do you maybe need to add some?

Then the next step is to figure out what pumps you need. This is not quite as simple as it sounds. You need both the potential head loss in the piping and radiation, and the desired flow. To get the desire flow, go back to your calculation on heat output. To determine the flow, generally a 20 degree drop from input to output is acceptable, and at that temperature drop you need 1 gallon per minute flow for 10,000 BTUh output. You look at the required BTUh in each loop, and divide by 10,000 and there's your required flow. From the head loss and flow you can pick a pump.

The best arrangement is what is termed primary/secondary piping. This is an arrangement where one pump -- and a relatively short piping circuit -- simply circulates water through the boiler. The secondary circuits take water from that primary loop and circulate it through your system. Take a look at this article: https://heatinghelp.com/systems-help-center/understanding-primary-secondary-pumping/ to help understand how it works.

Ironman

In addition to what has been stated, you need to check for orifice plates in the cast iron radiator valves. They would have originally been in the upper floor radiators when the system was gravity flow but should have been moved to the first floor rads when the system was converted to forced flow.

This is a major part of properly balancing old gravity systems.

Another thing to look at is the cleanliness of the old piping. If the original system is one that used the top of the rads to maintain an air cushion for expansion, in lieu of a compression tank, then there could be a lot of sludge in the old piping that's restricting flow.

There are articles in the systems help section of this site about these systems that are very informative.

Steamhead

I'd improve your insulation first. If that means putting off the boiler replacement, so be it. With better insulation you can go with a smaller boiler when the time comes.

All conversion burners are not created equal. What burner is in your old Delco boiler?

sokoloff

Last weekend I did the walkaround to calculate how much radiation I have. Using 185ºF water tables, I came to:
Zone 1 - Floor 1: 60K BTU/h + 19K BTU/h in the sunroom
Zone 1 - Floor 2: 20K BTU/h
Zone 2 - Floor 3: 16K BTU/h baseboard
Total: 115K BTU/h

At 215ºF, that becomes ~150K BTU/h.

Given that many of these radiators are cool/cold, it's not at all a surprise that the boiler cycles.

In doing the manual J calculations in the past, I struggled to identify what to put for some of the insulation values. It's a structural brick building with an air gap and then lath and plaster walls in most of the building. Double pane retrofit windows in most rooms. Insulation is R30 fiberglass in the attic roof rafters and blown-in cellulose above the 2nd-floor ceiling. One bedroom was remodeled by us and has closed-cell spray foam in the space available between the brick and the new plaster.

The rooms with "hot" radiators are sufficiently comfortable, indicating to me that if I could get all the radiators up to temperature I'd at least be in the ballpark of the building heat loss.

The location is Cambridge, MA.

sokoloff

Bob, the original system used a plain steel expansion tank in the basement (so did have the same possible issue you allude to). That's since been replaced with a bladder style expansion tank.

Steamhead, the burner is a 1991 Wayne P265F BB EPN, 65-200MBTU/hr input (natural gas). Gas is regulated to 3.5"WC (burner says 3.0-3.5"WC is acceptable).

Alan (California Radiant) Forbes

If you go to the top of this page and click Find A Contractor, there are 3 heating professionals within a 10 mile radius of you.

Zman

The tables usually assume a delta t of 20 degrees. Your deltas are much wider.

sokoloff

I'll draw out the piping system as you suggested above (good exercise for my own understanding anyway).

EBEBRATT-Ed

@sokoloff
Sounds like you not getting flow, could be the pumps or some other issue. You do have some long runs there. Since it's not an emergency.
Start with

Heat Loss as @Jamie Hall mentioned
Check installed radiation versus heat loss
size piping and boiler

As @Steamhead mentioned insulation , windows and doors will let you put in a smaller boiler and reduce installation costs and save on fuel.

If you follow the pipe and the temperature drops along the loop and nothing is air bound it's one of two things (usually) the pumps are to small or you have a restriction

sokoloff

Thanks to several posters who combined to whack me with a clue-by-four. Ed's last line was the final push, but others contributed as well. (The system help pages are a treasure of information, which led to me learning a lot more about my heating system than I ever expected to know.)

I purged the attic zone successfully and despite my prior efforts convincing me that it was well bled, it was not. A couple of obvious burps of air came out, right about when I was going to give up and call it "confirmed". The piping is not set up on the first zone for such easy purging, so I'm going to leave it alone for the rest of this cold snap, but I'll keep an eye on things.

The attic is warm again (as it usually was), the rest of the family is happy, and no one had to do a weekend service call. Good all around.

I'll pick this thread back up with more information about planning the boiler replacement. Thanks a million!

Steamhead

Good to hear. The original zone (1) would not have been set up for purging that way. There should be a bleeder on each radiator and that's where you get the air out.

That Wayne P265 is a rather primitive burner. The Carlin EZ-Gas, Midco EC, Wayne HSG and Riello burners are much better. But in an older boiler like that, it shouldn't do badly as long as it's properly set up and tuned. Someone from the Find a Contractor page would be able to do that for you, so the boiler can run at its best while you upgrade your insulation.

EBEBRATT-Ed

It's a good weekend to have heat!!!

nicholas bonham-carter

I wonder if, from your Radiator temperature reports, if your radiators are connected in series, instead of being in parallel.—NBC

mattmia2

Seeing how it is piped would help a lot. If i am reading right, it is zoned with pumps in the supply side and all of the zones are hot at the supply but very cool at the return.

Where is the t-stat in relation to the radiators that are heating? Maybe a much lower water temp, maybe 150 would heat better. Is it possible the system is set up with relatively low flow in the large radiators is heating the first radiator quickly and satisfying the t-stat before it gets a chance to heat the rest of the system.

Figuring out your heat loss at least roughly and the output of your emitter will tell you if it would work at a lower temp.

sokoloff

nicholas bonham-carter said:

I wonder if, from your Radiator temperature reports, if your radiators are connected in series, instead of being in parallel.—NBC

Zone 1 is piped in parallel. It seems like the first radiators get the bulk of the flow.

mattmia2 said:

Seeing how it is piped would help a lot. If i am reading right, it is zoned with pumps in the supply side and all of the zones are hot at the supply but very cool at the return.

Pumps are on the return side, pumping into a smallish manifold and then into the boiler unit itself. Supply comes out the top of the boiler through the original piping.

mattmia2 said:

Where is the t-stat in relation to the radiators that are heating? Maybe a much lower water temp, maybe 150 would heat better. Is it possible the system is set up with relatively low flow in the large radiators is heating the first radiator quickly and satisfying the t-stat before it gets a chance to heat the rest of the system.

This was my initial thought this fall as well. It looks like that is stymied by the first original fitting off the boiler on the supply side being a thermostatic union that's labeled as 180ºF. I think that is what's limiting my low temp experiments during the shoulder season.

mattmia2 said:

Figuring out your heat loss at least roughly and the output of your emitter will tell you if it would work at a lower temp.

Agreed. That and drawing the system as-built are my next steps.

Steamhead said:

Good to hear. The original zone (1) would not have been set up for purging that way. There should be a bleeder on each radiator and that's where you get the air out.

Yeah. That's why I thought I'd had things well bled, by using those things. I was wrong.

Steamhead said:

That Wayne P265 is a rather primitive burner. The Carlin EZ-Gas, Midco EC, Wayne HSG and Riello burners are much better. But in an older boiler like that, it shouldn't do badly as long as it's properly set up and tuned. Someone from the Find a Contractor page would be able to do that for you, so the boiler can run at its best while you upgrade your insulation.

I had a guy out to set the combustion and check things over. He seemed to be a little out of his depth at the particulars of the system (as am I, obviously), but was able to get the basic maintenance done and said they had an older guy who would be better able to discuss "these dinosaurs".

Alan (California Radiant) Forbes

What you have is a perfect setup for a mod-con boiler. Once you insulate the house and upgrade the windows, you can run lower temperature water to those large radiators and your boiler will be condensing most if not all the time which translates to lower fuel costs.

colinbarry

I used to live in a structural brick monolith of a house... 2 wythes thick with an airgap! The walls were always quite cold to the touch in the winter. The high thermal mass of the brick seemed to “radiate” the outdoor temperature inside. Have you ever noticed this?

Zone 1 piped in parallel... If the first radiators are getting hot you probably have some balance issues. If truly piped in parallel each radiator branch needs to be balanced unless the branches are designed to be equivalent in load and pipe restriction (head). You can test by closing the rad valves in the hot rooms and 1 or 2 of the others should heat up. Theoretically you could try to balance with the rad valves with the coldest rooms being fully open and the others being somewhere in the middle.

mattmia2

Oh, I did not catch the gravity conversion so it is piped in parallel. I was thinking series for some reason(although we don't know what they did when they converted it, so we don't know if it really is piped as parallel.) Could be some restrictor plates in the radiators as I think some have mentioned. Also worth it to open up a valve on one of the ones that isn't heating to see if the gaskets have disintegrated and clogged it up.