Help experimenting with lower temps for my baseboard

In_New_England

I have, what I assume is, high temp baseboard.





My cast iron oil boiler (Weil McLain WTGO-4) is set to deliver 180F water to the baseboard and for the DHW storage tank.

I'm trying to figure out if high temp air-to-water heat pumps would at all work in my case. If I lowered the boiler temp to 150F would this

1. Be ok for my SS-lined chimney
2. Be ok for my DHW (legionella wise)

How low could I go with the WTGO-4 before it was inadvisable for the boiler/chimney?

Thank you!

In_New_England

I do see that they recommend a secondary loop system (forgot the technical term for it) if the system temp is less than 140F, so I'm guessing that's the lower limit to which I should fiddle with?

(This link, section "Piping for systems requiring
temperatures below 140°F")

mattmia2

The short answer is that the return water temp shouldn't be sustained below 130 degrees once the system is up to temp and it needs to be running long enough cycles that it gets up to temp.

The longer answer is someone that understands combustion and draft better than I do should be looking at the stack temps going in to the vent to make sure that there won't be sustained condensation in the boiler or the vent.

JohnNY

The fin-tube output is 140°-150° isn't much. Your boiler will condense at around 140° and you'll spend considerable money trying to protect the boiler with a bypass loop. This sounds like a not-so-awesome idea.

In_New_England

JohnNY said:

The fin-tube output is 140°-150° isn't much. Your boiler will condense at around 140° and you'll spend considerable money trying to protect the boiler with a bypass loop. This sounds like a not-so-awesome idea.

Points well taken. Firstly, I don't want to change my oil boiler piping - I just want to figure out where I stand between needing 180F all winter to never needing more than, say 150F the vast majority of the time.
I want to figure out of my existing baseboard system would conceivably work with a lower temperature heat source.


What is the design difference with "Low temperature baseboards" like this Designline Synergy one and mine? The Designline Synergy ones deliver quite a lot of BTU/ft at 140F for example.

JakeCK

a2w heat pumps really aren't a good match to baseboard from what I have read. And testing that by setting the aquastat on your boiler so low as to risk condensation in the HX and flue is not a good idea.

In_New_England

JakeCK said:

a2w heat pumps really aren't a good match to baseboard from what I have read. And testing that by setting the aquastat on your boiler so low as to risk condensation in the HX and flue is not a good idea.

Yes, I've seen similar information, but I have also been hearing about things like this: https://www.daikin-ce.com/en_us/product-group/air-to-water-heat-pump-high-temperature.html which piques my interest.

Hot_water_fan

It’s quite possible to supply 150 or much lower water to the radiation while still preventing condensation with mixing. 

In_New_England

Hot_water_fan said:

It’s quite possible to supply 150 or much lower water to the radiation while still preventing condensation with mixing. 

If I understand correctly, this would require new near boiler piping, which is then not feasible for just an experiment, sadly.

Hot_water_fan

If I understand correctly, this would require new near boiler piping, which is then not feasible for just an experiment, sadly.

If the experiment is to see if lower water temperatures will work with baseboard, the answer is definitely yes - manufacturers provide ratings at different water temperatures. Dividing your heat loss by your linear feet can show you what temp you need for design day. For all other days, a lower temp is needed so you can figure out where the crossover is. 

Another method would be to measure supply and return temps constantly, seeing what your average water temp is at different outdoor temperatures. Of course, you could also just keep the existing boiler and install an air to water heat pump. 

Jamie Hall

I tried to find out some information on the units -- technical information -- which you would need to evaluate whether the heat pumps which you mention would work. At all. Seems to be unobtanium, but perhaps you can get more information.

You need several bits of information to evaluate this. First, what is the actual building heat load? Second, at what temperature does the water going to your baseboards have to be to meet that load? Third, can the heat pump deliver that temperature water with your design day outside air temperatures?

If the answer to the last question is yes, might be worth giving it a shot. Otherwise, you would need your boiler still on the chillier days -- a somewhat dubious proposition.

On the baseboards -- the main design difference between your conventional baseboards and the ones designed to run at lower temperatures is that the latter have a lot more radiating area per foot of baseboard.

JohnNY

Jamie Hall said:

On the baseboards -- the main design difference between your conventional baseboards and the ones designed to run at lower temperatures is that the latter have a lot more radiating area per foot of baseboard.

...
...Which the existing pump and pipe diameters may not support.

ScottSecor

I suspect this question had been answered many times before on this site. However, since we are all concerned about the cost of utilities lately I'll jump in and share my thoughts.

You mentioned you were concerned about your boiler water temperature for dhw proposes, as you are worried about legionella. Assuming your boiler is fitted with a tankless coil, I would think it's likely set to hold at least 130 degrees year round so you can wash your hands or take a shower whenever you desire. In most homes and buildings we take care of that have (or had) tankless coils the aquastat setting for dhw was more often than not set to 140 or 150 degrees. At 140 degrees you can pretty much rule out Legionnaires. IF you set your tankless coil at say 120 degrees, I would bet you'd run our of dhw before you finished showering on a summer day. Keep in mind that many residential gas fired water heaters here in NJ are set between 105 to 120 degrees all the time....

I think your considering lowering your high temperature limit for the heating side to turn the burner off earlier and save some fuel along the way. This is not a terrible idea, as you likely do not need 180 degrees but for a few days of the heating season. In many homes and buildings you might get away with 150 degrees if the structure is well insulated and over radiated. In your case with regular old copper fin hwbb, I doubt you would get away with say 150 degrees on the coldest winter days. As you may know regular hwbb only produces about half as many BTU with 140 water as compared to 180 degree water.

Now, some ideas that may go against the grain to think about.
1. On many cast iron cold start boilers, they start up at room temperature (typically 60-70 degrees here in NJ basements) and operate until the thermostat is satisfied or the aquastat is satisfied, whatever happens first. This might take five minutes with a "high speed"/low mass system like copper finned hwbb -or- maybe as long as a few hours with a "low speed"/high mass system like a older home with a thick (non insulated) concrete slab with copper radiant.

In this example, the boiler would theoretically condense at any temperature below 130 degrees (some say 140 for gas). Yet, we see this type of system almost daily around here and these boilers sometimes last thirty or forty years.

2. On a few cast iron boilers with tankless coils that stay warm all year, regardless of outdoor temperature, the boiler water temperature dips significantly when the heating thermostat first calls. In fact some of these cast iron boilers get so cold that they have a reverse acting aquastat that turns off the circulator to prevent the person in the shower from screaming bloody murder. Imagine a house that was converted from gravity to forced hot water and the radiators and piping hold massive amounts of ambient water just as the thermostat clicks on.

In this example the boilers could also condense until the temperature comes back above 130 or 140 degrees. Yet they also can last as long as above.

What I'm trying to say is yes, we design to prevent flue gas condensation whenever possible with cast iron boilers. But with all cold start boilers (including steam I might add) they are prone to condensing inside the boiler and I assume the flue. Yes, I realize that in a normal heating cycle in the dead of winter most cast iron boilers will not be condensing. In the end, you could try to lower your aquastat and see what you can get away with. You may find things start to leak that were not so obvious before...

mattmia2

In_New_England said:

What is the design difference with "Low temperature baseboards" like this Designline Synergy one and mine? The Designline Synergy ones deliver quite a lot of BTU/ft at 140F for example.

The enclosure is about an inch taller and deeper than standard baseboard and the fins are about an inch larger in both directions so the fins have a lot more surface area.

dirtbike59

You could change out the hydrostat with say a Hydro level 3250 and use outdoor air temp input and let it vary the water temp. I been happy with my setup doing that. I do have the dwh indirect on priority so the system will ramp up to 180 to heat that. Otherwise the 2 baseboard zones heat with whatever the oat calls for. 

In_New_England

Thank you all for your very helpful advice/knowledge.

I have some calculations from earlier this year, using a worksheet and then doing a sanity check looking at my historic oil consumption. In brief, heat loss at different outside temps are

1. 41 kBTU/hr at 0F
2. 35 kBTU/hr at 9F
3. 20 kBTU/hr at 32F
4. 14 kBTU/hr at 45F


I have 87' of baseboard. The outputs, according to the slant fin chart, are

1. 28 kBTU/hr at 140 F
2. 33 kBTU/hr at 150 F
3. 40 kBTU/hr at 160 F
4. 44 kBTU/hr at 170 F

I suspect the answer is typical for my kind of house, for my area, around Boston:

We can get by with 150F except for a few days in winter, and it puts us just outside the safe range of current air-to-water heat pumps.

Bummer. I was hoping to avoid ductless. I will be asking questions about ductless/high velocity shortly ...

JakeCK

In_New_England said:

a2w heat pumps really aren't a good match to baseboard from what I have read. And testing that by setting the aquastat on your boiler so low as to risk condensation in the HX and flue is not a good idea.

Yes, I've seen similar information, but I have also been hearing about things like this: https://www.daikin-ce.com/en_us/product-group/air-to-water-heat-pump-high-temperature.html which piques my interest.

Daikin pulled out of the US heat pump market I thought?

fentonc

There are a variety of air to water heat pumps at least theoretically available in the US now (Chiltrix, Enertech, Taco System-M, arctic, etc.) - they all usually top out with around 130F water temps. The strategy they all seemed to have settled on is to pair the heat pump with an electric boiler (sometimes integrated into a buffer tank) in a way that the heat pump can communicate with the boiler to hit the target number of BTUs in the most cost-effective manner. You could also do a dual-fuel setup of some sort with a gas or oil boiler. You just need to meet some target heat loss (looks like 41K BTU/hr for you if 0F is your design temp), so you can either increase your radiation (either add radiators, or swap to high-output/low-temp radiators - baseboards, panels, fan coil units, radiant floors, etc.) to get more output at lower temperatures, add in something like an electric backup to raise the temp, or reduce the heat loss in your home until the numbers all work out.

I did a bunch of experiments with this last winter with my 'boilertron' monitoring setup - I mostly have the same baseboard you do, but I have like 150' of it across 3 zones and my house's heat loss is only like 24K BTU/hr at the design temp, so I would probably be fine down to 110F-120F water. To avoid condensation though, mine just runs on an aquastat with a high limit of 160F and a low limit of 140F before it kicks back on.

hot_rod

As Scott mentioned, in some cases the boiler shuts down before seeing adequate return temperature. I suspect at some time during the season it does see longer run cycles and dries out the chimney evaporates any condensation 

The key would be measuring the flue temperature at the roof top. B vent would warm quickly, brick and outdoor masonry chimneys, probably not as quickly

Another inexpensive return temperature method is a setpoint control that drops off the circ until the boiler warms. Even the entry level Viessmann boilers use that method. They use a triple well with operating control, high limit, and return temperature probes all in one location in the boiler.

No doubt it cycles the circ a lot on mild days, but it would be inexpensive to try

A 10 minute run cycle seems to be what the industry agrees on, both for cycle wear, and getting the block and chimney above condensing temperature 

If the brick or b vent cap is all corroded, good chance the boiler has been run extended cold conditions 

Hot_water_fan

We can get by with 150F except for a few days in winter, and it puts us just outside the safe range of current air-to-water heat pumps.

Bummer. I was hoping to avoid ductless. I will be asking questions about ductless/high velocity shortly ...

Not so fast! You have a few more options. These aren’t exclusive: 
1. keep the oil boiler for a few days per year
2. use electric resistance for a few days per year 
3. use a high temperature water to water heat pump (Nordic is a manufacturer), which can get you to about 160.
4. Slightly reduce heat loss 
5. slightly increase radiation

The Steam Whisperer

ScottSecor said:

I suspect this question had been answered many times before on this site. However, since we are all concerned about the cost of utilities lately I'll jump in and share my thoughts.

You mentioned you were concerned about your boiler water temperature for dhw proposes, as you are worried about legionella. Assuming your boiler is fitted with a tankless coil, I would think it's likely set to hold at least 130 degrees year round so you can wash your hands or take a shower whenever you desire. In most homes and buildings we take care of that have (or had) tankless coils the aquastat setting for dhw was more often than not set to 140 or 150 degrees. At 140 degrees you can pretty much rule out Legionnaires. IF you set your tankless coil at say 120 degrees, I would bet you'd run our of dhw before you finished showering on a summer day. Keep in mind that many residential gas fired water heaters here in NJ are set between 105 to 120 degrees all the time....

I think your considering lowering your high temperature limit for the heating side to turn the burner off earlier and save some fuel along the way. This is not a terrible idea, as you likely do not need 180 degrees but for a few days of the heating season. In many homes and buildings you might get away with 150 degrees if the structure is well insulated and over radiated. In your case with regular old copper fin hwbb, I doubt you would get away with say 150 degrees on the coldest winter days. As you may know regular hwbb only produces about half as many BTU with 140 water as compared to 180 degree water.

Now, some ideas that may go against the grain to think about.
1. On many cast iron cold start boilers, they start up at room temperature (typically 60-70 degrees here in NJ basements) and operate until the thermostat is satisfied or the aquastat is satisfied, whatever happens first. This might take five minutes with a "high speed"/low mass system like copper finned hwbb -or- maybe as long as a few hours with a "low speed"/high mass system like a older home with a thick (non insulated) concrete slab with copper radiant.

In this example, the boiler would theoretically condense at any temperature below 130 degrees (some say 140 for gas). Yet, we see this type of system almost daily around here and these boilers sometimes last thirty or forty years.

2. On a few cast iron boilers with tankless coils that stay warm all year, regardless of outdoor temperature, the boiler water temperature dips significantly when the heating thermostat first calls. In fact some of these cast iron boilers get so cold that they have a reverse acting aquastat that turns off the circulator to prevent the person in the shower from screaming bloody murder. Imagine a house that was converted from gravity to forced hot water and the radiators and piping hold massive amounts of ambient water just as the thermostat clicks on.

In this example the boilers could also condense until the temperature comes back above 130 or 140 degrees. Yet they also can last as long as above.

What I'm trying to say is yes, we design to prevent flue gas condensation whenever possible with cast iron boilers. But with all cold start boilers (including steam I might add) they are prone to condensing inside the boiler and I assume the flue. Yes, I realize that in a normal heating cycle in the dead of winter most cast iron boilers will not be condensing. In the end, you could try to lower your aquastat and see what you can get away with. You may find things start to leak that were not so obvious before...

The one thing to add to a the above, is that all older cast iron boilers tend to "heat soak" after shut down. The pump usually shuts off at the end of the call for heat and the very hot castings are still transferring heat to the water. This drives up the boiler temperature and typically will dry out the castings between cycles. This is one of the reasons why properly set up bypass piping works for high mass systems. With the newer controls running the pump after burner shut down, this may interfere with this drying cycle of the boiler.

In_New_England

Hot_water_fan said:

Not so fast! You have a few more options. These aren’t exclusive: 
1. keep the oil boiler for a few days per year
2. use electric resistance for a few days per year 
3. use a high temperature water to water heat pump (Nordic is a manufacturer), which can get you to about 160.
4. Slightly reduce heat loss 
5. slightly increase radiation

I suppose I'm too stuck on getting rid of the oil boiler. Now that I've been forced to replace the oil-tank, I've greatly reduced the danger of an oil leak, so the only economic negative of the oil boiler is the running cost. So your suggestion of a hybrid system is excellent (1, 2), though I would have to hunt for a contractor with experience in such things.

(3) Is intriguing. Do you mean a ground source heat pump? I think this is too expensive to be worth it. Or do you mean a different system?

(4) I haven't tried beyond attic insulation and basement and other sealing. I have double paned windows and foam insulation under the siding (can't tell you the rating).

(5) Interesting: would I replace a few of the baseboards with larger radiators/low temp baseboard, likely after doing a heat loss in different rooms, in order to size the overall system to match a given air-water heat pump?

Hot_water_fan

@In_New_England

3) it’s a ground source heat pump without the ground loops. The air source would heat water up to say 90 and the water to water would take it from there. Like this: https://www.nordicghp.com/wp-content/uploads/2022/10/002531SPC-01-ISSUE-02-WH-55-H.pdf

the appeal of this would be that on the coldest days, you’re avoiding resistance heat and might eek out a COP of 2, which can help with amperage constraints. 

5) yes. Idronics covers this well. 

Two levers more or less - raise water temp and/or decrease water temp needed. 

WMno57

The Steam Whisperer said:

The one thing to add to a the above, is that all older cast iron boilers tend to "heat soak" after shut down. The pump usually shuts off at the end of the call for heat and the very hot castings are still transferring heat to the water. This drives up the boiler temperature and typically will dry out the castings between cycles.

Sounds a lot like my 75 year old boiler. High mass and high volume (converted gravity system). No Bypass. Warm start. The aquastat and pump are completely separate from each other. Not efficient, but the MTBF is outstanding!

In_New_England

MikeAmann said:

If you haven't done so already, spray foam insulating your rim joists is the single most effective way of combating heat loss.

I believe the nice folks contracted via MassSave did that as part of the insulation upgrades to the house. I have the spray foam and insulation batts pressed into the space above the concrete foundation where the framing sits.

In_New_England

Hot_water_fan said:

3) it’s a ground source heat pump without the ground loops. The air source would heat water up to say 90 and the water to water would take it from there. Like this: https://www.nordicghp.com/wp-content/uploads/2022/10/002531SPC-01-ISSUE-02-WH-55-H.pdf

the appeal of this would be that on the coldest days, you’re avoiding resistance heat and might eek out a COP of 2, which can help with amperage constraints.

It took me a moment to get that. I was like, "Yes, but where does the warm water come from??" before I realized that the setup can be understood as the first heat pump (the air-to-water heat pump) as faking the Earth. That is, the first ASHP extracts heat from the air and makes the fake ground loop lukewarm. Then the WSHP extracts the heat from that fake ground loop and boosts it higher.

I suppose the engineers have worked it all out so that the COP > 1.

Thanks for that tip. It sounds horrendously expensive, but who knows, in the next five years (which is my time frame) it might be affordable tech.

HomerJSmith

There is no such thing as a free lunch, my Dad always said. To run baseboard at a lower temp and meet the envelope heat energy loss and meet setpoint can be problematic.

First, you need enough heat emitters to put the needed BTUs into the room, but that can be problematic. A short baseboard run, running at higher temperature can put out as many BTUs as a long baseboard run, running at lower temperatures. But...too long a baseboard run and you run out of heat energy before you heat the last baseboard in line. It's a balancing act.

Fuel economy is built into the boiler. However, lowering supply water temperature (SWT) to what is needed is a savings in the long run. But, there is a limit on how far you can lower it. Boilers are designed to operate within certain parameters. Sometimes you can fudge it.

It's all a balancing act, a trade-off, whether to spend money for improvements in boiler sys efficiency or pay the higher gas prices. That's life, we're constantly making value judgements.

ronbugg

Go to Slant Fin, download heal loss app. Do a room by room heat loss. Take heat loss numbers (btuh) needed and compare them to fin tube baseboard output. Slant Fin temps listed from 220 degrees down to 110 F, With this info you will know minumium design T. Wirenut

pedmec

Idont know about bugs in the software but slantfin closed down and the baseboard manufacturing was sold to mestek. i would call mestek to find out whats up with the software. they are in westfield, mass.

ronbugg

Go to TacoComfort they have Hydronic System Solutions HHS - Hydronic Systems. Never used it. Good Luck

Robert_25

MikeAmann said:

I was hoping that a member downloaded it in the past and still has a copy that I can get my hands on.

I had a copy for a long time, will look on my old server and see if I still do.