New Viessman has a long recovery time after night set-back

John_9

I have a new Viessman hot water oil fired boiler. My home has 4 zones - DHW, first floor baseboard, second floor cast iron radiators, and third floor baseboard. The first floor is the largest zone. There is copper baseboard on all the exterior walls, and no room left for anymore. The boiler temp high limit is set at about 95 degrees C, although the thermostat on the boiler usually reads about 88 degrees C when the boiler goes off on high limit (the heating contractor doesn't think this difference makes much difference). In the morning, after a 4 degree night setback, it can take up to 1.5 hours for the room temp (first floor) to move up 4 degrees (from 60 to 64 degrees). This is when it is cold outside (about 25 degrees) and no other zone is calling simultaneously. The windows are weather stripped and in fairly good shape. How can I get the first floor zone to recovery more quickly? Isn't 1.5 hours a long time to wait for a 4 degree recovery? The oil company who installed the system appear to be stumped. Help!

Mike T., Swampeast MO

Possibilities

1) Too much baseboard in the loop.

2) Inadequate flow through the baseboard loop.

3) Supply temp too low (the 7° Celcius drop between expected and actual high-limit could be quite significant if the B/B loop was tightly designed with a 95° supply in mind).

4) If the boiler uses outdoor reset, the curve might be too shallow or too low in magnitude.

Steve Ebels

What did

You have in the home before? Were there any other changes made to the piping when the new boiler was installed? Does the burner on the Viessmann run continuously during the pick up time frame or does it cycle off and on? If it's cycling that would indicate a problem other than the capacity of the boiler so you can eliminate that from your trouble shooting.

Keep talking, we'll keep answering.

John_9

Thanks to Mike and SE for their responses so far. A couple of points of clarification - the 30 year old system that was there before had pretty much the same problem with pick up as the new system, although it was slightly faster; the loop has been split onto two sections (one about 60% room size, the other 40%); there is no outdoor reset; the burner doesn't run continously during the recovery time - it reaches high limit relatively quickly; the circulator pump is a Taco 008 (had been a 007, but that was changed to make it circulate faster). Any other thoughts?

ScottMP

Slow recovery

MAybe do a heat loss and check how much heat you need for upstairs. If the boiler is shutting off then it has the capacity to heat the room. You may be under what you need to heat the room.

Just a thought.

Scott

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Nick_3

How much does the water temperature drop going through the zone? If it drops a lot, you probably lack adequate water flow. If it does not drop much, your baseboard radiators may be blocked by carpet or may just be dirty. Also, make sure the fins on the tubing are not turned so that the bent fins are on the top and the bottom.

Steamhead

Does each zone

have its own circulator, or do you have one circ and several zone valves?

Also, how much baseboard (in feet) is on the problem zone?

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Steve Ebels

Is

All the baseboard getting hot. Does it feel uniform in temperature?

How'zat for getting pelted with questions???

Ya ask one and get 25 in response. But that's how good detective work is done.

John_9

The return water comes back to the boiler at about 180 F or so. The first floor zone has it's own circulator (Taco 008) and seems to move the water pretty well. Did some balancing of each loop, and the temperature is fairly uniform throughout the whole zone. Thanks for the ideas so far. Looking forward to more.

chuck shaw

some more questions

What size is the pipe leaving the circulator, and returning to the boiler? Is the circulator "facing" the correct way? What size is the baseboard? If the two split loops, and the common piping for the supply and return are the same size, neither will work as well as it could. Personally, if I am spliting a zone, with 3/4" copper fin, I like the common piping to be at least 11/4". It may not have to be that size, but I have never had a problem doing it that way. Also, if the system is balanced with "butterfly" valves, or with gate valves, or if there is an old gate valve in the system, there may be something broken, restricting the flow. Because this was close to the same with the old system, look towards something that was not changed Just a few thoughts, hope one might help.

Chuck Shaw

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heatboy

Where are you from?

There may be someone here relatively close to you.

Warm Regards,

hb

climatecadvanced.com

"Expert in Silent Warmth" ™

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Chris Maderia

Delta -T

Your Delta-T is exactly what it should be based on your description of the boiler high limit. 95 degrees celcius is 200 farenhite. You stated that you were coming back at 180. Circulator is doing it's job, the boiler is doing it's job. Your problem to me seems to lie in that you do not have enough baseboard in the room.

Before set-back you have alot going on in the home, bodies, appliances, lights, solar gain so it seems that the heat is adequate when it's really not. At night when there isn't anything going on and you lose that solar gain then you motice the problem.

My recommendation to you is to get a new heat loss of the structure before you do anything else. You'll most likely will discover the problem. Best of Luck.