Your thoughts on my OWB performance

[MVrana]

.....correct line size and pump size wins out everytime.....

Absolutely. Like I said before, I'm trying the two pumps as a band-aid. I hope to get things set up correctly next summer. I just don't have the time or $ right now to pull and replace the lines. Once I do get it set up right, at least I'll have an extra Taco 009 on the shelf for backup.

Ghitch, I absolutely respect and appreciate your experience and input. I'm trying your suggestion (from another post) about decreasing the flue outlet size to 4". I'm anxious to see if it helps with my wood usage. Thanks for your input!

 

[ghitch75]

your welcome...lol

 

[ohioburner]

Post a link to the other post about decreasing the flue outlet. That is something I might try.

 

[ericjeeper]

First thing I would do is..... Take that set back thermometer deal out and toss it into a yardsale bin., Set the heat at 68 and leave it there..
The reason you see such high temps at the startup is the H coil has been sitting there dormant with hot water flowing through.. Once the blower has ran a while it has taken all the heat out of it.. And those 5/8 lines won't flow enough btus to keep up.
So let the furnace cycle a few times throughout the night.
In the half hour how far has the boiler temp dropped? from 190° to what?

 

[MVrana]

Post a link to the other post about decreasing the flue outlet. That is something I might try.

Not sure how to link a thread. If you do a search you'll find it. It is titled Modify OWB for Better Efficiency.

 

[MVrana]

What is the water temp inside the boiler when this happens? Comparing the boiler water temp when the furnace 1st kicks on to boiler water temp after you notice the outlet temp drop should give you the answer .Is your boiler water actually dropping 30 degrees? If it is, its not a flow problem, your boiler just cant recover fast enough. (possibly normal)if your boiler temp isn't dropping 30 degrees you have a flow problem....at least this makes sense in my pea brain

I found last year I was better off just leaving my thermostat the same.By trying to raise the house temp rather than maintain it, it would drop the boiler water temp to much and it takes to long for the fire to catch back up to demand.

Checked the boiler water temps this morning. 183 F when the furnace first starts heating. 143 degrees after the heat has been running for about 30 minutes. Based on this result, it sounds like the water capacity of my stove is just too small for my heat demand. Any suggestions for how to help the stove recover faster? It's a forced draft system, which I thought were supposed to recover quickly.

After seeing these numbers, I am now questioning whether it makes any sense to install larger lines from the boiler to the heat exchanger. Clearly I am pulling plenty of heat out of the water. Thoughts? If I just leave the t-stat at one temperature, the system seems to be able to keep up just fine.

 

[projectsho89]

Your assessment is correct. You don't have enough stored BTUs and the boiler can't recover quickly enough. I have the same situation. My house has enough interior volume that it takes about 30 minutes to raise the interior of the house 1 degree F when the outside temp is mild. When it's bitter cold outside, it takes as much as 45-60 minutes per degree.

I've tossed around the idea of getting several large water heater to use the tanks as hot water storage units, but I think it will just be easier to eliminate or back off the amount of setback I've programmed.

What's the water capacity of your system? Mine's rated at 175 US gallons.

You can try opening the draft damper a bit more to get a hotter fire, but eventually, you will end up blowing more heat out the chimney than you'd like.

 

[MVrana]

What's the water capacity of your system? Mine's rated at 175 US gallons.

My stove is a Hardy H4. It only holds 130 gallons.

 

[1harlowr]

I've got an H4 heating a 3000+sq ft house and DHW. There should be no problem with what you are wanting your OWB to do. Try leaving the t-stat at 68 over night and see what happens. I've got four 5/8" lines and two hot water tanks. Flow isn't a problem. If I did the lines again, I'd use 3/4" lines as my plumbing inside is 3/4".

 

[Windwalker7]

Does your draft blower have damper/flapper on it?

Or does it have a manually adjusted damper flapper?

In other words, when your furnace draft is off, is there a flap that closes off all the air automatically?

 

[ohioburner]

I have a Heatmor 200 (forced air) which holds less water then yours and I have my programmable t-stat set to turn back to 63 at night and back to 71 during the day. I am heating 3000 sq ft house and it keeps up fine. I also heat a 1200 sq ft garage but only to 50 unless I go out to work in it. I got 1 inch lines going to heat exchangers with a pump on each loop. I got my aqua-stat set at on 120 off 140 right now for this mild weather and I'm losing 8* across the HX in the house.

Would a bigger pump or moving one pump in by the heat exchanger move the water faster? I would think the faster the water moves the less water temp drop you would have across the HX and less cold water going back to the furnace.

 

[rob206]

Checked the boiler water temps this morning. 183 F when the furnace first starts heating. 143 degrees after the heat has been running for about 30 minutes. Based on this result, it sounds like the water capacity of my stove is just too small for my heat demand. Any suggestions for how to help the stove recover faster? It's a forced draft system, which I thought were supposed to recover quickly.

After seeing these numbers, I am now questioning whether it makes any sense to install larger lines from the boiler to the heat exchanger. Clearly I am pulling plenty of heat out of the water. Thoughts? If I just leave the t-stat at one temperature, the system seems to be able to keep up just fine.

What I think is happening is you are losing too many btu's across the HX, which may indicate a flow problem. I would think more flow would reduce the amount of btu's across the HX. In my system I see about a 10 degree drop. When I had my CB4030, which holds 140ga of water, it had no problem coming back up to temp and it was natural draft.

My opinion, your furnace with forced draft should have no problem recovering, no matter how many gallons of water it holds.

Just to elaborate on my CB4030, our house is 1900sq ft, but with vaulted ceilings. When we would turn up the t-stat in the morning the furnace fan would run for hours on end if it was cold outside. By cold I mean low 20's and colder. Still our boiler had no problem recovering.

 

[KsWoodsMan]

My stove is a Hardy H4. It only holds 130 gallons.

Is there 130 gallons in it. If it was low on water it wouldn't have the surface area needed to extract the heat needed for your house from the firebox.

After sitting there idling all night is the fire still going or just barely making it ?

Is it down to just a few coals and has run out of fuel ?

 

[Scootermsp]

I am heating 4500 sg/ft plus DHW with a CB5036. I set my first floor back to 50F at 6:20PM and back to 69F at 6:40AM. The KEY to doing this is to be up before the first floor calls for heat. I go outside around 6:20 - 6:30AM and rake out the coals and put in some good sized rounds onto the coals. By doing this you feed the OWB before it has a chance to drop down. What also helps is that the upstairs zones are set to drop BACK a couple degrees at the same time so that all zones are not competing for the heat at the same time. When the first floor calls for heat the DHW may also call for AM showers(2nd floor not calling). By having your OWB all set up to "RAGE" for a couple hours it will be better able to keep up with demand. I believe you will also see improvement by going to 1" lines. Hope this helps MV.

 

[MVrana]

Thanks for all the additional feedback everyone.

Windwalker7, the system is a forced draft. It has a flap that closes off, but there is a small hole that allows just enough air to keep the fire alive. The blower kicks on and the fire picks up quickly when the jacket temp drops below set point.

Ohioburner and Rob206, I am curious about your comments on the temperature drop across the heat exchanger. Why would I want such a low temperature drop (8-10 degrees)? It doesn't sound very efficient to me to extract such a small amount of heat and keep moving the hot water back and forth between boiler and heater exchanger. Doesn't that just add to heat losses throughout the system? Since BTU's delivered is a function of both flow and temperature change, maybe there are different paths to getting the same results (high flow at low temp change = low flow at high temp change)??? Am I missing something here?

KSWoodsman, the boiler is at a full 130 gallons. There is an auto fill valve with float to keep it at the right level. Also, there is plenty of wood and hot coals left in the morning. When the combustion blower turns on, the fire picks up pretty quickly. Then, depending on how cold it is, it burns for about 30-60 minutes before reaching temperature and shutting down. Does that sound like an unusually long burn time?

Scootersmsp, I have recently adjusted the timing and temp changes for the two zones I'm heating. This seems to be helping. I ususally rake out the coals and load the boiler in the morning just as the first zone is calling for heat.

Thanks again everyone. Great input.

 

[KsWoodsMan]

Thanks for all the additional feedback everyone.

.......

KSWoodsman, the boiler is at a full 130 gallons. There is an auto fill valve with float to keep it at the right level. Also, there is plenty of wood and hot coals left in the morning. When the combustion blower turns on, the fire picks up pretty quickly. Then, depending on how cold it is, it burns for about 30-60 minutes before reaching temperature and shutting down. Does that sound like an unusually long burn time?

........

Thanks again everyone. Great input.

I don't use an OWB so I'm not completely familiar with the entire operation or recovery time of one. I am threorizing and throwing out ideas that seem relavant to your problem. 30 - 60 minutes doesn't seem out of line for recovery time while also trying to bring the house back up to temperature.

The last one that comes to mind for me is this, Is the supply line for the pumps/HX connected to the top or the bottom of the boiler?
The supply line SHOULD be conected to the top connection to draw off the hottest of the water available. If it is connected to the bottom fitting you are drawing 'cold' water from the bottom of the tank.

It wont change your recovery time but it will help your house warm up quicker if you are drawing the hottest water available to your system out of the boiler and through your HX.

 

[12vdzl]

To me it sounds like you need more flow. 8 to 10 degrees temp drop across the HX sounds fine, because you're flowing ALOT of water through and keeping the water hot coming in and hot going out, while still exchanging plenty of heat. If you're having a temp drop of 30 + degrees, your water is slowly making its way through the HX dropping the temp too much to be able to keep up with the furnace fan to provide the heat needed.

A HX is based on BTU output by it's size, both outside dimensions, and the thickness. In order to put out the proper BTU's for it's size it has to have HOT water flowing through all the way to the end (output side). Hot water on the input side, and cold water on the output side, is a flow problem.

Hope this helps, it's the best way i can describe it.

 

[ohioburner]

The way I see it and I could be wrong is: If I am moving 15gal a min. and you are moving 5gal a min. I am loosing 8* and you are loosing 24* we are getting the same btu out of the water but my water is warmer going back to the OWB. Hope that makes sense and If I am wrong I hope someone corrects me.

 

[projectsho89]

The problem is *NOT* flow rate, it is the combination of the lack of adequate stored thermal capacity plus a recovery rate that cannot keep up with the rate of demand.

If it were insufficient flow rate, the temperature of the boiler wouldn't drop so quickly. The BTUs are being moved from the boiler to the house quickly enough, but they are not being replaced at the rate they are moved.

 

[yodayoda]

The problem is *NOT* flow rate, it is the combination of the lack of adequate stored thermal capacity plus a recovery rate that cannot keep up with the rate of demand.

If it were insufficient flow rate, the temperature of the boiler wouldn't drop so quickly. The BTUs are being moved from the boiler to the house quickly enough, but they are not being replaced at the rate they are moved.


[/QUOT:agree2:

I've found it just works better to leave my thermostat turned up, instead of turning it down at night and up in the AM