OWB ? House too warm

[Oxford]

The problem is inside, where the hot water goes into the furnace plenum whether there's a call for heat, and then the problem is more or less universal in location, since the laws of physics dictate that less dense things rise. This means the warmer, less dense air around the heat exchanger rises, creating natural convection, which overheats the space. It's not difficult or complicated at all, and is a perfect illustration of why so many OWB installations turn into clusters: people don't bother to think about what they are doing, or about any kind of load calculations, or about wood consumption, or about really anything at all other than Sticking It to the Propane Guy. Welcome to open windows in winter.

 

[Need2Saw]

Bingo, 3 way valve. One side is supply, one is to the heat exchanger and the third should be piped as a bypass to the heat exchanger and be sent back to the boiler. When the thermostat calls for deman water sent to the heat exchanger. The bypass can be tied into the pipe downstream if the heat exchanger, just remember to use a check valve in-between the tie-in and the HTX.

there is no need for a check valve

Also, @AIM, there's nothing wrong with the stat.

Have you tested both thermostats?

 

[AIM]

Oxford... What do you heat with????
I'm not saying convection isn't the problem but I have a REALLY hard time buying into it. 87° house while 15° outside???? Seems like a hell of a stretch.

 

[superw6]

Make sure thermostat isn't set to "circulate" which turns on the fan at 20 minutes out of every hour .if it's variable fan they move very slowly so make sure it isn't spinning without cutting your finger. Air exchangers installed after home is built tie into return air only and are wired into furnace fan turning it on every time you push washroom timer or de humidistat . Lastly, if all else is right give us duct and coil measurement as some clown has probably oversized furnace and duct by 2 then wood boiler idiot shoves cool in that fits hole instead of btu output. Sell boiler , heat with gas and be happy [emoji6]


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[beaglebriar]

Couple questions: Is the basement ceiling insulated? If not I can see the living space possibly overheating due to convection if the heat coil is way oversized. If that ceiling is insulated and the exchanger is too big I can see the basement getting pretty warm but the insulation should mostly stop that heat from entering the living space. Do you know that the boiler is operating properly? If the draft control isn't closing tightly you could easily be pumping 200+ degree water to the house also adding to your problem. I have a similar setup minus the heat exchanger as I use hot water not forced hot air. I have never had my house too hot. If it truly is getting too hot just by convection that place must have wicked good insulation.

 

[NSMaple1]

Couple questions: Is the basement ceiling insulated? If not I can see the living space possibly overheating due to convection if the heat coil is way oversized. If that ceiling is insulated and the exchanger is too big I can see the basement getting pretty warm but the insulation should mostly stop that heat from entering the living space. Do you know that the boiler is operating properly? If the draft control isn't closing tightly you could easily be pumping 200+ degree water to the house also adding to your problem. I have a similar setup minus the heat exchanger as I use hot water not forced hot air. I have never had my house too hot. If it truly is getting too hot just by convection that place must have wicked good insulation.

We don't really know yet, and maybe wouldn't without more info & maybe some decent pics, but insulation won't stop the flow if the flow is convection inside the plenum & ductwork. Which I could easliy see with an oversized HX and the right plenum/ductwork conditions. It actually might make it worse by keeping the air on the outside of the plenum warmer - depending on the layout. I think he already said the boiler maintains the right temps - around 170? I also would suspect that you don't have hot boiler water flowing 24/7 through your rads? (Or whatever you have for emitters). Usually hot water systems are better controlled - and as we see here, a hot air system with a coil adapted that pumps 24/7 often is not.

This is a good thread with lots of learning potential - hope the OP comes back with more info & follows through on some suggestions & gets things working better & shares it all.

 

[beaglebriar]

True I didn't take the duct work into consideration. My boiler room gets plenty of convection heat and even on a warm day it doesn't get ridiculously hot. I see the need for a dump zone but the OP is going to have to determine how and where to set that up. Garage would be ideal.

 

[Guswhit]

I almost hate to jump in this thread, but why not share my story! A few years ago, the wife and I went on vacation in March. When we left it was only getting up to mid 30's during the day and teens at night. I had a buddy stop out twice a day and load the stove so everything would be okay with the furnace and my inlaws were going to be staying in the house for the last couple of days with the kids before we got home. We had shut the thermostat down inside to 62 before we left. Well the temperature outside suddenly warmed up into the 70's for a few days and with the house being closed up and just the convection through the exchanger the house temp inside had warmed up to 80. I had a 3 valve bypass system set up on the furnace, but of course no one but me new how to operate it and the kids and inlaws had to vacate. So it is possible to convection warm up, but I find it hard to believe when its 15 outside.

 

[hupte]

another idea that would help would be to turn the aquastat down to about 150.

 

[Deleted member 117362]

The problem is inside, where the hot water goes into the furnace plenum whether there's a call for heat, and then the problem is more or less universal in location, since the laws of physics dictate that less dense things rise. This means the warmer, less dense air around the heat exchanger rises, creating natural convection, which overheats the space. It's not difficult or complicated at all, and is a perfect illustration of why so many OWB installations turn into clusters: people don't bother to think about what they are doing, or about any kind of load calculations, or about wood consumption, or about really anything at all other than Sticking It to the Propane Guy. Welcome to open windows in winter.

I agree with you. I have the same stove and my house is 1500 sq. ft.. I replaced my larger 434 with the 3300. All that is needed is to bypass some of the hot water. Cannot turn that stove down much more, without building creosote. If it's warm outside, my air handler will not run and my house heats up, I just open the bypass. Also run a high temp water filter on your stove to extend your pumps life. It's amazing how much scale the filter catches.

 

[AIM]

I'm gonna go ahead and lay a bet on the furnace fan controls. The fan is about the only thing that could get those temps up that high. Miswired stat or something? Something told the fan to run... Don't know what but my bet is on the fan controls.

 

[Deleted member 117362]

I agree AIM, but he said the furnace was not running. If the furnace blower is running, that is his problem.

 

[Oxford]

Which part of "the furnace blower was not coming on" and "the house is 1000 square feet, including the basement" is so hard to get your heads around? If the basement is the same size as the main floor, the house is 20'x25', almost exactly the size of a two car garage. It's not going to take much to (over)heat that. Remember, whoever remodeled the house figured it was tight enough that they put an HRV air exchanger in to bring fresh air in. That little house is tight, and you might very well be able to heat it with @AIM 's two candles. Next time you fire that boiler, after it's come up to temperature, put a dollar bill on top of one of the heating registers. I'll bet that selfsame donut against the hole that it floats up in the air, even with the blower off.

 

[Coldfront]

Yes the house is really tight, new windows and doors as well as lots of insulation. After reading your house dimensions of 20'x25' I realized I was way off I don't know what I was thinking. The house is about 1000 sq. ft. on one level with full basement 2000 sq. ft. It is a lot better now with all the heating vents shut. I think a bypass loop is needed out to the garage. I read that it is not good to run a owb water temp below 160 so I am going to leave it at the factory setting of 170 there is nothing wrong with the boiler itself it maintains a water temp of 170 damper fan shut off and kicks on again at 160. It is not hard to cool off by cracking a window or 2 open. Better to have a problem of too warm than too cold anyway. I will update if we find anything else on the problem. She said it got up to 80 in the house today @ 37 degrees outside temp. Just too much warm water going through that heat exchanger. I bet if you put some type of a damper in the duct just above the heat exchanger you could stop some of the heat convection, or it just might need a smaller heat exchanger. We need some below zero weather to really know if the furnace fan ever needs to kick on?

 

[AIM]

OK that makes a bit more sense. 3 bedrooms in 1000 sq, ft. is tight.
I'm still doubting the convection theory. Must be some AWESOME insulation!
I have 1080 per floor. Basement included is 2160. Not great but decent insulation. NO way convection will heat my house!

 

[Coldfront]

I haven't spent the night there yet so I am going by what she is telling me is going on. I will have to spend a night there and see what is happening for myself if that furnace fan is really not coming on. When I had a house with a wood burning furnace in the basement the furnace fan blower would come on by itself no matter what the thermostat was turned down to if the temperature in the furnace plenum got to hot, like some kind of a safety switch turns it on.

 

[logger450]

I had the same problem years ago in my little 800 square ft house. I had a huge central boiler that was way overkill but I knew I was gonna be moving and wanted the big boiler. The tiny house was great but then it started to get hot. It ended being the 3 way valve that was pictured in one of the earlier posts here. There is a rubber ball the is in the valve that seals off the flow when heat is not needed. The ball actually got distorted and let hot water thru the system. I took the top cover off and replaced it. There is also a little lever on the side that can manually lock the valve open. Hopefully this will help.

 

[AIM]

I think my point is being lost here. The SIZE of the outside unit has NOTHING TO DO WITH INDOOR TEMP.... Unless it's to small to keep up with demand...

170° water is 170° water NO MATTER WHAT SIZE UNIT IS HEATING IT....

The problem is indoors....

The ONLY thing an oversize unit will affect is wood consumption.... The heat exchanger and house doesn't know or care what is supplying the hot water..

The problem is indoors...

 

[hupte]

Yes the house is really tight, new windows and doors as well as lots of insulation. After reading your house dimensions of 20'x25' I realized I was way off I don't know what I was thinking. The house is about 1000 sq. ft. on one level with full basement 2000 sq. ft. It is a lot better now with all the heating vents shut. I think a bypass loop is needed out to the garage. I read that it is not good to run a owb water temp below 160 so I am going to leave it at the factory setting of 170 there is nothing wrong with the boiler itself it maintains a water temp of 170 damper fan shut off and kicks on again at 160. It is not hard to cool off by cracking a window or 2 open. Better to have a problem of too warm than too cold anyway. I will update if we find anything else on the problem. She said it got up to 80 in the house today @ 37 degrees outside temp. Just too much warm water going through that heat exchanger. I bet if you put some type of a damper in the duct just above the heat exchanger you could stop some of the heat convection, or it just might need a smaller heat exchanger. We need some below zero weather to really know if the furnace fan ever needs to kick on?

you don't need a heat loop going to the garage. just a bypass loop that bypasses the heat exchanger. the boiler WILL NOT over heat. the only way to overheat a boiler is to leave the boiler door open.

 

[Whitespider]

I completely agree with AIM on two points, the size of the outdoor unit will only matter to indoor temperatures if it's too small, and I don't believe the overheating of the house is because of convective air flow. C'mon we're talkin' 87° inside, 15° outside... a friggin' 72° difference?? If there was that much heat from convective air flow alone you'd be able to feel it flowing from the vents as though a blower were running. Something else is going on... something has to be causing the circulation blower to cycle on and off, at least on low speed. The blowers in newer furnaces are super quiet, you likely wouldn't even know it was running on low.

Two things come to mind...
1) There's an operator error issue with the thermostat settings. Not the "wood" thermostat settings, more likely the gas furnace thermostat settings... such as the continuous blower and/or circulation setting (which causes the blower to run on low speed).
2) The furnace has a switch/sensor which causes the blower to run at (low??) speed whenever plenum temperature reaches a certain point regardless, and independent of thermostat setting. In other words, the blower is running because the furnace senses heat above its heat exchanger... not because the thermostat is calling for heat. That is not a completely unheard of set up... the design intent is to keep the blower running after the burner shuts off until the heat exchanger cools to a desired point. It also doubles as a safety feature; if the circuit controlling the burner would malfunction and keep it fired, the blower will run to keep the heat exchanger from overheating and cracking... which would potentially put carbon monoxide into the home.
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