Boiler pump direction of flow

[awc]

Hello all,

I own a 1924 4-square that still has the original cast iron radiators, but the boiler was previously updated to a weil-mclain with a taco pump. Guessing that was done some time in the 80's or 90's.

I presume the original boiler was gravity fed with heat rising to the attic then falling down to the second floor then to the first floor. And judging by the large arrow cast into the front of the pump, the system is still pushing heat to the 2nd floor first. The 1st floor is noticeably cooler than the 2nd, and unless the temps really drop I typically keep the 2nd floor radiator valves closed.

- Since the system no longer relies on gravity, can the flow be reversed to push heat to the 1st floor radiators first?
- Is it as simple as flipping the pump upside down?


Thanks,
Tony

 

[Dana]

The boiler usually has a preferred direction of flow, simply flipping the pump isn't a great idea.

Breaking it into separate zones by floor is probably the right thing to do, but that is often a real PITA with old gravity flow systems.

A few pictures of the boiler plumbing and radiator plumbing might inspire some easier solutions.

 

[Sponsor]

 

[awc]

photos attached

 

[awc]

The boiler usually has a preferred direction of flow, simply flipping the pump isn't a great idea.

Breaking it into separate zones by floor is probably the right thing to do, but that is often a real PITA with old gravity flow systems.

A few pictures of the boiler plumbing and radiator plumbing might inspire some easier solutions.

photos below

 

[Dana]

You definitely don't want to reverse the direction of flow through the boiler. It might still work (since the boiler looks like an oversized behemoth), but the efficiency will take a dive.

It's probably fine to cut the plumbing to swap the supply & return to the radiators to reverse the system flow. I don't see any check valves in the boiler room pics, but the plumbing details around the radiators would be good to look at too.

Would it be practical to break the connection where the upper floor's radiators outflow comes back to the boiler room and the first floor's radiator supply comes straight from the pump? With a supply manifold & return manifold of tees, and a couple of globe valves for adjusting the flow to each flow separately it's likely you'd be able to achieve reasonable balance between zones.

The beginning of the heating season isn't usually the best time to start in with major hacks on the heating system. But in the mean time all of that big-diameter pipe in the boiler room is one big funny-looking radiator. Insulating it with 1" fiberglass pipe insulation (both supply & return) would be cost effective. That might knock a degree or three off the boiler room's temperature, but it's probably the warmest place in the house in winter.

Another thing that creates floor to floor temperature imbalance with the upstairs warmer than the downstairs is outdoor air infiltration. A multi story house with a basement has significant stack-effect pressures, a function of the vertical distance between the top of the house and the bottom of the house. Air sealing the upper floor ceilings and all plumbing/electrical/flue penetration caps the top of the stack, slowing down the outflow, sealing up every door/window/dryer vent, band joist & foundation sill in the basement blocks inflow into the very bottom of the house. Those air leak zones are by far more important than all the air leakage in between.

Take care to seal up any balloon framing that is open to the basement or attic, and any flue/plumbing chases that run basement-to-attic at both the top & bottom.

Flue chases f0r masonry chimneys can be sealed using sheet metal caulked at the seams with fireproof materials, not can-foam or anything flammable.

 

[awc]

You definitely don't want to reverse the direction of flow through the boiler. It might still work (since the boiler looks like an oversized behemoth), but the efficiency will take a dive.

It's probably fine to cut the plumbing to swap the supply & return to the radiators to reverse the system flow. I don't see any check valves in the boiler room pics, but the plumbing details around the radiators would be good to look at too.

Would it be practical to break the connection where the upper floor's radiators outflow comes back to the boiler room and the first floor's radiator supply comes straight from the pump? With a supply manifold & return manifold of tees, and a couple of globe valves for adjusting the flow to each flow separately it's likely you'd be able to achieve reasonable balance between zones.

The beginning of the heating season isn't usually the best time to start in with major hacks on the heating system. But in the mean time all of that big-diameter pipe in the boiler room is one big funny-looking radiator. Insulating it with 1" fiberglass pipe insulation (both supply & return) would be cost effective. That might knock a degree or three off the boiler room's temperature, but it's probably the warmest place in the house in winter.

Another thing that creates floor to floor temperature imbalance with the upstairs warmer than the downstairs is outdoor air infiltration. A multi story house with a basement has significant stack-effect pressures, a function of the vertical distance between the top of the house and the bottom of the house. Air sealing the upper floor ceilings and all plumbing/electrical/flue penetration caps the top of the stack, slowing down the outflow, sealing up every door/window/dryer vent, band joist & foundation sill in the basement blocks inflow into the very bottom of the house. Those air leak zones are by far more important than all the air leakage in between.

Take care to seal up any balloon framing that is open to the basement or attic, and any flue/plumbing chases that run basement-to-attic at both the top & bottom.

Flue chases f0r masonry chimneys can be sealed using sheet metal caulked at the seams with fireproof materials, not can-foam or anything flammable.

• perhaps the photo is distorting it, but the boiler is less than 30" inches tall. but point taken, i'll not "flip the pump".
  
• the 1st and 2nd floor share common supply and returns. as I have a crawl space and not a basement, splitting them into zones would be a significant and unpleasant project.
• regarding the chimney effect you're absolutely correct. one of the biggest improvements i made over the years was to seal the crawl space vents.

 

[Dana]

I was looking at the size of the stack, which looks like 6-7", implying a boiler well over 100,000 BTU/hr, maybe even 200,000 BTU/hr.

A random 2000' house with some fluff in the walls & attic and storm windows (or clear-glass non-low-E replacement windows would have a design heat load at Richmond's 99% outside design temp of +18F would be about 30,000 BTU/hr, maybe 40,000 BTU/hr @ 0F during the worst Polar Vortex event of the century. With it's efficient shape and modest window/floor ratio, a Foursquare would come in a bit lower than that. If there's nothing in the walls but air and no storm doors it'll still be less than 50KBTU/hr @ +18F. If you have some wintertime gas bills you can verify the limits of the heat load by figuring out the amount of gas burned per heating degree-day and converting that to a linear BTU per degree-hour constant, which would give a reasonably accurate load number at any arbitrary outdoor temperature using this methodology. (It's simple than it sounds- you're basically using the existing boiler to measure the heat load.)

With high mass radiators you'd probably do really well with a tiny modulating condensing boiler and a smaller circulation pump that runs almost constantly at lower water temperatures, using an "outdoor reset" approach, which raises & lowers the water temperature in response to outdoor temperatures. With lower water temps the amount of heat emitted by the upstairs rads won't be as much, and the temp reaching the first floor rads. I suspect your current boiler has to be oversized to keep from destroying itself with excess condensation as it heats up all that water in the system at the beginning of a call for heat. I don't see evidence in the pictures of system bypass or boiler bypass plumbing in the pictures to protect the boiler from return water that is too cool, which would allow use of a more appropriate sized cast iron boiler. With a modulating condensing boiler you WANT cool return water, since they're designed to be tolerant of condensation inside the boiler, reaping the heat of vaporization of the moisture that gets condensed out of the exhaust stream. When it's time to replace "the beast", a cheap fire tube modulating condensing boiler would be about the same or lower cost of a right-sized cast iron, and in your situation I'd expect it to cut the wintertime gas use by more than 30%. (The crawlspace temperture would be a lot cooler in winter, but that's OK- you don't live down there, and it's probably the warmest place in the house currently when it's freezing outside.)

 

[awc]

I was looking at the size of the stack, which looks like 6-7", implying a boiler well over 100,000 BTU/hr, maybe even 200,000 BTU/hr.

A random 2000' house with some fluff in the walls & attic and storm windows (or clear-glass non-low-E replacement windows would have a design heat load at Richmond's 99% outside design temp of +18F would be about 30,000 BTU/hr, maybe 40,000 BTU/hr @ 0F during the worst Polar Vortex event of the century. With it's efficient shape and modest window/floor ratio, a Foursquare would come in a bit lower than that. If there's nothing in the walls but air and no storm doors it'll still be less than 50KBTU/hr @ +18F. If you have some wintertime gas bills you can verify the limits of the heat load by figuring out the amount of gas burned per heating degree-day and converting that to a linear BTU per degree-hour constant, which would give a reasonably accurate load number at any arbitrary outdoor temperature using this methodology. (It's simple than it sounds- you're basically using the existing boiler to measure the heat load.)

With high mass radiators you'd probably do really well with a tiny modulating condensing boiler and a smaller circulation pump that runs almost constantly at lower water temperatures, using an "outdoor reset" approach, which raises & lowers the water temperature in response to outdoor temperatures. With lower water temps the amount of heat emitted by the upstairs rads won't be as much, and the temp reaching the first floor rads. I suspect your current boiler has to be oversized to keep from destroying itself with excess condensation as it heats up all that water in the system at the beginning of a call for heat. I don't see evidence in the pictures of system bypass or boiler bypass plumbing in the pictures to protect the boiler from return water that is too cool, which would allow use of a more appropriate sized cast iron boiler. With a modulating condensing boiler you WANT cool return water, since they're designed to be tolerant of condensation inside the boiler, reaping the heat of vaporization of the moisture that gets condensed out of the exhaust stream. When it's time to replace "the beast", a cheap fire tube modulating condensing boiler would be about the same or lower cost of a right-sized cast iron, and in your situation I'd expect it to cut the wintertime gas use by more than 30%. (The crawlspace temperture would be a lot cooler in winter, but that's OK- you don't live down there, and it's probably the warmest place in the house currently when it's freezing outside.)

• its been a while since i looked, but the boiler is rated at 110btu and i keep the temp reasonably low. and after 20 years i can almost tell what the outside temp is based on how often the pump is running.
  
• at one time i did look into one the high eff boilers, but after spending 2k to re-line a decaying chimney the idea of abandoning that investment lost its appeal.
• your comment about the bypass does answer one question i've always had: "why is the fresh water supply downstream of the boiler?" always wondered about that, but assumed it was to prevent thermal shock of the cast iron.

on another topic, i need to replace one of the upstairs radiators with a baseboard or shallow floor trench. any brand preferences?

 

[Dana]

Not really partial to a particular brand- fin-tube baseboard is all pretty similar. Some might have nicer fitting sheet metal than others, but performance is about the same.

Cast iron baseboard is a bit nicer heat, and you can often find it cheap on Craigslist. It paints up pretty easily, and is nearly indestructible. Don't buy any that have been dissasembled- it's PITA (and requires special tools) to re-assemble them in a leak-proof manner. Look for the cast-in foot on each end that gives the bottom of the cast baseboard an inch or so of clearance from the floor. Even nicer are European style flat panel rads, but that's a lot more expensive.

Whatever you do, but sure the BTU output of what you replace it with is at least comparable to the 180F average water temp is of the old radiator. You'll have to estimate it's square feet equivalent direct radiation (EDR) using this guide, and multiply the EDR' by 170 BTU/hr. Typical fin-tube is rated 600 BTU/hr per running foot, 8" tall cast iron base board about 550 BTU/hr per foot.

The fresh water supply can be almost anywere on the system- it's normally shut off, and only added when there's a need to air-purge or pressurize the system. Even with an auto-fill valve, barring a catastrohpic leak the amount of water loss is microscopic (should be zero), so there's really never a big gush of cold water entering the system while it's operating.

A high efficiency condensing boiler is usually side-vented out the house using plastic vent pipe, whereas an 86% cast iron would require an expensive chimney liner. Even a right sized legal-minimum 82% efficiency boiler would require a (cheaper metal, but still more expensive than plastic) liner to get the stack to operate correctly. The original chimney would be WAY oversized for a 40-75K cast iron boiler.