Radiant Heat and Woodstove

[bldvdb]

You guys and gals were wonderful in helping me select a Jotul Castine wood stove last fall. It took a few weeks but we got the hang of getting the stove to burn 24/7. I'm in love with it and looking forward to our first fire in the next month or so (we're in Maine).

I had our furnace cleaned today and mentioned to the tech that it seemed like the furnace and or exhaust were running a lot, practically nonstop during the winter. He said that having radiant heat and a wood stove isn't very efficient. That made me bummed! He said that the heat from the stove is heating the air and the upstairs but isn't heating the slab so the furnace runs a lot to heat the slab.

I'm not sure what to think. He didn't offer any solutions. I can't be the only person with radiant heat and a wood stove. How can I make them work well together.

We have a 1800 square foot cape built in 2009.

Any advice or help would be fantastic.

 

[begreen]

A furnace is for a hot air system. It sounds like this is a hot-water boiler feeding a radiant floor heating system. Is that correct? If so the difference between a radiant and a convective stove may not be the issue here. It could be heat loss from the slab. Last winter was particularly cold so the system had to work hard, especially if the slab insulation is not great. The solution for that might be to increase the house's perimeter insulation around the slab.

 

[DougA]

My guess is that are burning at too low a temperature. I don't own that stove but it should provide enough heat for 3/4 of your house if burned hot. Many people think a stove running at 350 is hot. It's not enough heat for what you need from what you are saying.

Radiant heat means that is heats the objects in the room (walls/furniture, etc.) better than it heats the air. The reality is that once the objects are warm, the air gets warm from them. Even then, a radiant heater will absolutely heat the air also. It's simple physics. Is your furnace hooked up to a radiant heat system in your ceiling? We need more clarification on that.

It appears that your house is built on a slab, just like mine. Slabs will always feel cool, even when room temperature. Slabs also suck heat from the room. Once again, simple physics that a very dense object pulls heat energy from less dense objects. In our area, everyone has put ceramic tiles on their floors and then wonder why their feet are cold all winter. Duh???

Let us know what temps your are normally running the stove at and more about your furnace and we can give you better answers.

 

[bldvdb]

I'll need to get more information on furnace/boiler. I have all the manuals in the utility room off the garage.

I do try to keep the wood stove around 500.

 

[Grisu]

I looked at one of your older post where you mentioned having baseboards upstairs. That would suggest a boiler system. (Heating hot water and delivering it through pipes to radiators.) Are there baseboards downstairs or does your floor warm up when you turn on the heat? Where is the thermostat located?

 

[bldvdb]

I do have two zones. Upstairs we have baseboard heat with a thermostat in one of the two bedrooms. Downstairs there are no baseboards and the thermostat is around the corner from the wood stove.

 

[Nick Mystic]

It seems like you aren't sure of the type of heating system you have since you called it a furnace and then a furnace/boiler, which I've never heard of. Regardless of what it actually is the simple solution to your situation is to just turn the thermostat way down on the heating system and then it won't turn on when you are burning your stove. Then check the temperatures in various areas of your house to see how good a job your stove is doing keeping things warm. Maybe you'll find the stove is able to keep the temperature within a range you're comfortable with. If there are areas where you think it is too cold and other areas that are warm enough for your taste then you can start developing a plan to remedy the situation. For example, if only a small part of your house is cooler than you like it you might be able to get by with a small electric heater in that area when you are occupying it. Or, perhaps you could get a plumber to set up a separate zone for the cold areas and just run the boiler to heat those areas.

 

[Grisu]

And where does the heat come from when you turn up the lower thermostat? It sounds like floor radiant heating. What was that lower thermostat set to?

Since it is two zones it may also be possible that the boiler was working to keep the upstairs warm. You will need to play around with both thermostat settings to figure out which part of the house your boiler supplies when the stove is running.

 

[bldvdb]

Yes, it is floor radiant heat downstairs. We keep it set very low, around 60-64 (I'm cheap!).

I'll clarify what I actually have in that utility room when I'm back home. I know there is a furnace and I think two tanks (one for the radiant and one for heating water?). I don't know about this stuff which why I'm asking you.

 

[begreen]

That is a boiler, not a furnace. No need to check, furnace systems don't have radiant floor heat and baseboard radiators.

Were you comfortable last winter with the stove running at 500F? In our house I had to run the Castine closer to 600F during very cold winter to compensate for heat loss of the house. That ate up a lot more wood and shortened burn times by a couple hours. This is why we went to a stove almost twice the size of the Castine.

If you were comfortable last winter with the Castine running around 500F then I would set the radiant heat lower, like 60F this winter and try that. If you need longer burntimes or more heat then you probably need a larger stove.

 

[bldvdb]

Well I haven't paid off the stove that I bought so a new one is out of the question.

There were weeks in the dead of winter when the temperature didn't get above 0 for days that the stove needed to be filled every four or so hours. Other than that, it was fantastic.

I'm finding this thread very helpful and am going to look into a thermostat in the floor rather than the wall. https://www.hearth.com/talk/threads/radiant-slab-heat.129581/

 

[begreen]

Sounds like the stove is definitely helping keep you more comfortable and it has to be contributing to a heating reduction. There may be core design issues with the house that are harder to address. Slab insulation and isolation would be an example. If you want more heat or longer burntimes you might ask the stove shop if they would take the Castine in on a trade up to the Oslo.

What fuel does the boiler run on? If oil you are in luck with lower costs this year.

 

[bldvdb]

Both the furnace and boiler run on number 2.

 

[begreen]

Wait, you have a warm air furnace and a boiler? It's remotely possible but that seems unlikely.

 

[DougA]

The bottom line is that you need to keep your house reasonably comfortable to live in. Turning the thermostat down will only work if the stove can make up the difference. As begreen said, you seem to be under sized on the stove but that's not an option right now. I would crank up the heat to 600 and I think you will find a big difference. You can be sure that the wood stove is keeping your oil cost lower. If you are buying wood, I would do the calculations for this coming winter and you may find that oil is cheaper. This winter, there will be a lot of people burning wood only when they are home to use the heat.

The castine is smaller and you will find a much shorter burn time when running at 600. It's the heat you need, not the burn time. I would spend the time and money to add insulation and lower air infiltration everywhere you can. In almost all cases, adding insulation is the most cost effective way of saving money and having a more comfortable house. Adding area rugs in the winter on any floors that are hardwood, concrete or tile will add a very measurable warmth and help insulate from the slab.

 

[bldvdb]

Wait, you have a warm air furnace and a boiler? It's remotely possible but that seems unlikely.

I have base board heat in the upstairs of the house. Radiant heat in the downstairs. I used the term furnace and someone corrected me that it was a boiler. So, there, I think I have both!

I just got off the phone with the oil company and I used 25% less heating oil after adding the wood stove. So that is good I guess. Maybe this year I can figure out how to bump that number up.

 

[Grisu]

I just got off the phone with the oil company and I used 25% less heating oil after adding the wood stove. So that is good I guess. Maybe this year I can figure out how to bump that number up.

A less cold winter would help. Most people saw an increase of 25% in their heating fuel consumption. I also assume you were more comfortable than with the boiler alone.

 

[begreen]

I have base board heat in the upstairs of the house. Radiant heat in the downstairs. I used the term furnace and someone corrected me that it was a boiler. So, there, I think I have both!

Very unlikely. A single boiler is probably feeding both the radiant heat and the baseboard heat through different zones on the same system. Neither the radiant heat nor the baseboards connect to a furnace. A furnace is for ducted hot air which has not been mentioned in this house.

Sounds like the wood stove saved a bit of money in spite of a very cold winter.

 

[firefighterjake]

Furnace = heated hot air pumping out of ductwork

Boiler = heated hot water (well I guess "heated" and "hot" are redundant in radiant heating systems and baseboard heaters

You most likely have a oil boiler.


To my knowledge (and folks correct me if I am wrong), radiant systems work pretty similarly to conventional baseboard where a wall mounted thermostat measures the air temp and that determines whether the heat comes on or not. In this case I would guess it shouldn't really matter if you have a radiant woodstove or convective or combination.

You might try working the stove a bit more . . . possibly seeing if there are any other ways to tighten up the house or add more insulation . . . but I think the first thing I would do is kick the thermostats down a bit and during the course of the winter see just how cold it is getting in the various rooms. It may be that one zone is cooler than the others and calling for heat and perhaps adjusting the way the heat moves (with the woodstove and floor fan) will change things up.

A few other items of note . . . unless you have an on-demand oil boiler it will fire up periodically throughout the day -- this is normal and it will use some oil.

As noted . . . last year was particularly cold and perhaps even more important . . . very long . . . and I say that as an avid snowmobiler. We heated for a very long time last year.