Constant Circ to balance room temp? Or add more baseboard

Tonerlow

We have a Veissmann 200W retrofitted in a 1250 square foot bungalow. The south bedrooms are 10 degrees F colder overnight when the ambient temp reaches -40 up here. Of course opening the door equalizes the temp, but then kids are not sleeping well.

Best solution is to add baseboard to the 2 rooms? I have all dampers closed in the rest of the upstairs. Add foil on top of the fins the try and push more heat into these 2 rooms? (I am assuming they are on the cold end of the loop)

I read another thread yesterday about utilizing constant circ to equalize room temps. In your opinion would this be helpful in this situation? (all fin tube radiators).

Or am I better off to bite the bullet and increase the amount of radiators in the colder rooms?

Increasing supply temp, I'm guessing will not help, as it will just satisfy the thermostat quicker and the same issue will persist?

Jamie Hall

How to solve the problem deispends a lot on how the system is piped. If it is piped in series, that is one unit of baseboard feeds the next, which feeds the next, and so on in a single loop, it may prove to be almost impossible, although your attempt to reduce the heat output of the upstream baseboards will certainly help. Increasing the flow rate will also help, although that may mean a higher capacity pump, as the temperature drop along the loop will be less. Switching to constant circulation won't make much difference, I'm afraid.

The ultimate solution is to split the loop, if you have access to the piping in some way, so that you can control the flow to the bedrooms separately from the flow to the rest of the system. Then you can use independent thermostats to control the temperatures, and also balance the flow so that the bedrooms get more heat as needed. This may -- or may not -- be all that easy to do.

hot_rod

Do a room by room heatloss to see if you have sufficient baseboard in all the rooms

HomerJSmith

First, you need a boiler capable of delivering the required BTUs. Second, you need the piping that can distribute those BTUs. Third, you need a pump capable of moving the heated water from the source to the heat emitters. In a way it's complicated. All designed sys take all that into consideration.
It may be as simple for you to install a larger pump to increase the flow or as Jamie Hall says, split the zone. The solution depends on the design of your sys. You need to provide a lot more information and pics.
Adding baseboard isn't going to help you if you don't have the heat energy or flow.
This is where you take a laser thermometer and measure the input to the first radiator and the output of the last radiator. Put a piece of black electrical tape on the copper pipe and shoot that tape.

Tonerlow

I'm going to assume the house is plumbed in 2 series loops, one for each floor.
There are Tees in the boiler room on supply and return. Bought it 7 yrs ago, built in '76.

The basement ceiling is finished so changing piping will be a big endeavor I would rather avoid.
If we were going to that extent then I think I would just change over to staple up floor heat upstairs, and cut out the baseboards.

Mustangman

Piping is critical. Remember you can only get so many BTUs out of a 3/4" pipe @ 4 gpm. If you have a series loop where you are in and out of baseboard and the return end becomes a supply for the next piece of baseboard. Once you get to 65' of baseboard, your supply water temperature has dropped below the desired 20 degree Delta T. You need to count the footage of baseboard and see where you are. If the rooms giving you trouble are near the end of the loop beyond that 65' of baseboard, the only real cure is to split up the loop with a 1" return. Put 1/2 of the baseboard on the branch of a 1x3/4 x 3/4 return tee and the balance on the other 3/4 port of the tee. You will need to install isolation valves on each branch and a purge valve just after the shut off valves. The 1" return will go back to the boiler and tie into the return.. This splits your load down low enough that you won't be trying to heat the space with 140 degree water. You still need your total footage of baseboard so you can place the 1x3/4x3/4 where it will best serve you. Good luch

Tonerlow

@mustangman @HomerJSmith
thanks for your input. Changing the piping is definitely a last resort, finished basement ceiling, do not know how the system is piped due to this. If I was going to take on a full basement Reno then we would have installed forced air rather than a new boiler I think. Neighbours just did this in their house a few years ago, built around the same time (mid70s)  by same builder. Funds are currently not there to take that on. I would love to change the top floor over to in floor if I could convince the wife one day. But that is probably lower priority than windows, flooring etc. 

I will definitely try shooting some temps, boss has a snap on thermal cam that’s quite handy. 

One of my main concerns is how the boiler room is piped, he has a 1/2” ball valve installed as a bypass to allow boiler pump to run constant. 

I have had concerns for some time that the “far” upstairs rooms are not receiving enough flow because it would be possible it is short-cycling try the bypass? 

Also unknown is if this has been an issue since 1976. We didn’t use these south rooms with the doors closed that much when we bought the place, and replaced the boiler, then had kids and now are finding that the rooms stay cool. 

I closed all other dampers upstairs and bumped the shift up +6 for tonight. See if this makes any difference. 

Pic of boiler room. You can see the bypass just above to left of boiler. Supply lines tee off above boiler, zone valves are visible. Returns coming thru wall on the left hand side. 

The small flare fittings on the zone valves have also made me question flow rate in the past 

thanks for the input. 

Tonerlow

Also worth noting. It is “design day” weekend here with ambient temps of -40 

hot_rod

The pump to the right may be the system pump. I believe that version is a 3 speed. There may be a speed switch on the black plastic cover. Bumping the speed up will get you a bit more output also. Temperature increase is a better option, but I don't know that fixes a balance issue.

Do you have the manual for the boiler? It may not be piped as they suggest? I'm used to seeing primary secondary or a low loss header. Or maybe there is a LLH off to the left? Take a pic from back aways.

Most 1/2 or 3/4" zone valves are a 7- 8 Cv. plenty of flow capacity for your system.

Tonerlow

@hot_rod It is piped direct…… Don’t get me started. Contractor cut out a high temp cast iron boiler and put in this, with no thought put into it. IMO 

Yes I have the pump cranked up to high, usually performs pretty well on medium until we hit -25C or so 

Tonerlow

One day I should bite the bullet and pay someone to do this and change the programming 

hot_rod

Yeah, the deck is stacked against you with that install. I'd start over with a proper LLH installation.
Don't let Viessmann see that install it, they'll choke on their weinerschnitzel

Tonerlow

Just woke up to give the kid a bottle. The bedroom is toasty, but the main living space has dropped 3F below the setpoint overnight. Opened a couple dampers, farthest ones from the thermostat. Will see how many I have to open before it recovers. 

It’s -41C here right now so this is a good design day test for it. 

Maybe this summer I will bite the bullet and get quotes on a repipe. Or start hounding the installer about it again. 3 yrs since install now though…..

HVACNUT

Hey, I just learned -41 is the approximate meeting point of C and F. And it only took me 56 years. For a second there I thought Google was broke or I entered the Twilight Zone.
Anyway, Viessmann is all about constant circulation. An indoor sensor. An outdoor sensor, and off you go. But of course it must be designed and piped correctly. 
Maybe the least invasive would be to replace the thermostat with something like a Honeywell T9 where you could connect wireless sensors.

Tonerlow

@HVACNUT I do believe -40 is equal in both temps 

Ya I have read a little bit about indoor sensors, these will still have limitations based on my piping though? 

What I do know is that the programming in my VEISSMANN is being under-utilized. It is capable of so much more that maintaining return water temp. Which is about all it does right now as far as I know. 

And recognizes a DHW call, because it modulates up to satisfy that. 

HVACNUT

Tonerlow said:

What I do know is that the programming in my VEISSMANN is being under-utilized. It is capable of so much more that maintaining return water temp. Which is about all it does right now as far as I know. 

And recognizes a DHW call, because it modulates up to satisfy that. 

I'm no Viessmann pro as far as setup and addresses with their boilers. I would have to sit down with the manual. I know there are some Viessmann pros here. Maybe some settings changes can be made. Even if it means sacrificing efficiency for comfort (sorry Germany) until the proper corrections can be made.

hot_rod

I have two remote sensors on my Ecobee. One in the finished basement, one under the kitchen sink for freeze protection

When enabled it basically runs the furnace to keep the basement at a comfortable temperature when we have guests. The upstairs overshoots by 3 degrees or so. So there is a compromise to that logic.

Same with multiple temperatures from a boiler control. It can only do one temperature at a time, it just tries to average out the heat delivery to the multiple different temperature loads.

Both methods treat the symptom not the problem.

In your case this may or may not be workable. If you need more than a 3 degree spread, it could make the majority of the home uncomfortably warm.

It is a non invasive thing to try, the cost of the stat and sensors instead of a repipe or upgrading heat emitters.

If you go for a heat emitter upgrade, go with high output instead of adding additional footage, it will be easier than moving pipes to accommodate longer fin tube.

It sounds like the room(s) is just under radiated?

Tonerlow

@hot_rod Ya I suspect there is just not enough radiator for a mod-con boiler, where with the old high temp one there was. And ya there are high output rads by both of our entries, I can definitely tell the difference in the amount of heat being emitted. 

Also there are stacked radiators?, but these would likely require moving electrical plugs higher on the wall, moving gyproc etc. 

Tonerlow

Basically our whole upstairs has a rad under each window, at the entries, short one in both bathrooms, and a little extra in the living room and kitchen. 

What’s missing is any piping on the west wall, these are the rooms that stay colder, no surprise as that is our prevailing wind direction up here 

hot_rod

If it can heat the space at say 180, certainly you could allow the mod con to go to that temperature when needed.

Usually the relationship is fairly linear. As outdoor drops, SWT goes up the same proportion. So 70- 80% of the heating season you should be below 180. But perhaps not in condensing mode very often.

If changing one or two fin tubes allowed you to run in condensing mode more often, it might be worth the upgrade?

Formulas here to determine that. A heatload calc for a single room should take 10- 15 minutes so you are not guessing on the size upgrade.


https://www.caleffi.com/sites/default/files/media/external-file/Idronics_25_NA_Lowering water temperature in existing hydronic heating systems.pdf