Newbie to the idea of radiant heat in a 1200 sq ft home

Josh342

Hello everyone,

I recently joined the group because I wanted to gain some knowledge on a radiant project that I want to put myself through. I have been reading a lot online and watching a lot of youtube videos but the more I read and watch, the more I am confused as to the direction to go. I have found some useful videos but you know how youtube can be.. find 2 ways to do it right and 10 ways not to do it. So that brings me here..

I have a two story cap cod home in Ludington Michigan. It is a 1200 sq ft home with replacement windows. It currently has forced air but the furnace is severely out of date and was set up with incorrect sized ducts and are minimal to second floor. The price was way too high to upgrade due to the ducts needing improvement.

When I measure the basement, I get roughly 800 sq ft. The main floor is 9 ft ceiling and the upstairs varies due to the roof line.

My thoughts were to go with a radiant floor (between joists) on first floor and radiators in each room upstairs. The main floor consists of a living room, dining room, kitchen, master, and bathroom, along with stairway. The second floor has three bedrooms.

I have read some people using tankless water heaters. I have seen some using the Takagi brand, specifically. I thought about going this way and use a heat exchanger to keep potable separate. Then I read a post on here regarding the BTU output when dealing with the circ, which the post went way off into the weeds but I got the point of it. It makes sense. So.. what to do, what to do..

I am on a budget and would like to try to make this work.

I have attached my floor plan as a rough drawing that I did at work yesterday.

Any thoughts?

Larry Weingarten

Hi @Josh342 and welcome! Everything starts with a heat loss calculation. Or perhaps the heat loss can be teased from your energy bills. Best would be a room by room heat loss number. With that figured out, the right system design becomes possible.

Yours, Larry

Josh342

I am looking online for a heat loss calculator. I have found a couple but some appear to be confusing. Sorry, I am not familiar with doing this. What I am finding is this, Room volume x Delta T x Air Changes per Hour x . 018.

As for Delta T, I would imagine it would be around 70 because that is where I would want my internal temp and we do see some 0 degree weather here in Michigan. As for the Air Changes per hour, how do you calculate this?

Hot_water_fan

It's difficult to add a radiant heat retrofit if you're on a budget. Can you supplement heat upstairs somehow? Seems much cheaper than tossing a furnace and installing all the necessary hardware. You have two upstairs bedrooms - keeping the furnace and adding two electric baseboards should work.

Josh342

Is the correct calculation, Q = U x Area x HDD x 24 x .75? If so, I got 55,762,560 BTU's. I think this is for insulation though. After looking at my basement perimeter, I found my sq ft is not 1200 but infact 1560. I do not have consistent 8 ft walls upstairs though.

hot_rod

see if this one works:

https://slantfin.com/slantfin-heat-loss-calculator/

US Boiler has one, and I see a few apps in the store

I would guess more around 40,000. But run some numbers.

Transfer plates from below, check to see how accessible the floors are, few if any nails protruding?

franzsf

I installed something similar in my first house, which I still own.

It all works, but (1) you will probably rely far more on the radiators than the in-floor radiant and (2) don't expect to be condensing (low return water temps) in the winter. I operate somewhere between 140 - 160 from Nov - March, depending on how cold it outside.

As the other folks have said here, do the heat loss first, and be very realistic about what kind of flux to expect from a under-floor radiant retrofit.

Josh342

I did the heat loss calculator from slant fin. I got a result of 34066. 

hot_rod

That is a bit more believable

Hot_water_fan

https://www.supplyhouse.com/Cadet-2F500W-30-F-Series-Electric-Baseboard-Heater-500-Watt-240V-White?gclid=CjwKCAiAwc-dBhA7EiwAxPRylCMEp3QeyfxoZQeIUDtKO_uRBoi6JCqIwxf3V4x9s72r13LVLT8_BxoCGssQAvD_BwE

500w electric baseboards for upstairs are just $40 each 

Josh342

This doesn't fix my main floor situation. The furnace needs to be replaced. I am not discounting the electric heater. It's definitely an option as I wouldn't need to tear up my walls and ceiling downstairs. I appreciate your help. 

Hot_water_fan

What’s the main floor issue? You said upstairs ducts were undersized and you are on a budget, but nothing about the main floor, unless I am misunderstanding. Part of the beauty of a small house is that you don’t need much heat and can avoid expensive heating systems. Right now, you are looking at a pretty expensive option. 

Josh342

The furnace is from the early 70s. There are 4 or 5 small round tubes extending outwards.  These tubes are around 4 inches each. I had a couple estimates that were around $15k because of the duct issue. The furnace cycles on/off more than it should.  My gas bill is around $200 a month. 

I would also like to open the basement for future improvements. 

bburd

That sounds like a duct system designed for a high temperature induction furnace, which was a thing back in the early 1960s. They supplied high temperature air (over 250° F IIRC) and mixed it with room air at the supply registers. I believe they went out of production due to safety hazards associated with the very hot air, and/or poor energy efficiency. Unfortunately, newer furnaces are not compatible with that type of duct system. It simply cannot move enough air at the lower supply temperatures (typically about 140-150° F these days) that most furnaces produce.

Josh342

Yes, exactly!  I'll have to show pictures later. Living room, dining room, and my bedroom has a vent about 7 feet up and a vent about a foot off the floor. They are both connected and it was explained that it's supposed to help circulation of air. 

Hot_water_fan

Sounds good - how much gas did you use last year? In therms, not $. 

Are you planning to keep the ductwork? You could repurpose it as a chase for the upstairs pex. 

hot_rod

If you go with radiant, do it right. Aluminum transfer plates, a boiler not a tankless water heater, adequate insulation, proper piping, etc.
nothing is cheap now, so you can add your labor. Price out components now that you know size of equipment. Figure tube and plates 8” on center to ballpark that cost

Josh342

This is my furnace. Lots of small pipes. 

Josh342

bburd

Yes, that appears to have been a high temperature induction system originally. Sadly, that ductwork won’t be much use with any modern system I know of.

Josh342

Bburd, I see you set me a message. The problem with the duct work is that for the upstairs, I only have one register. And the dumbest thing that they could have done was to have the register facing into a bedroom. On the other side of the wall is the open area of the second floor where the stairway comes up. It makes absolutely no sense that they would have placed the radiator on the bedroom side. Unfortunately, if I run pex tubing to the second floor, it is going to have to go through walls and ceiling. It is 95% plaster in the house. I think some of the walls in the stairway area are drywall otherwise everything is plaster. That means cutting the plaster and the lathe.  

bburd

It may be possible to fish pex through the existing duct, using it as a chase; then install your radiator in front of the existing register location.

hot_rod

panel radiators are a nice option or mix with radiant. Sleeping rooms are a good match for panels with individual TRV control. Possibly run one temperature to radiant and panels

bath, kitchen and great room radiant, panels elsewhere 

Josh342

@Hot_water_fan My energy company does not let me look at the actual data (for some reason). I looked at a statement for Feb '21, which was the highest month. I used 8.6 CCF's which converts to 8.29 Therms.

Josh342

@bburd The vertical duct is something that I thought of. Not sure if 1 radiator panel in the entry area would be sufficient to heat everything though.

Hot_water_fan

@Hot_water_fan My energy company does not let me look at the actual data (for some reason). I looked at a statement for Feb '21, which was the highest month. I used 8.6 CCF's which converts to 8.29 Therms.

Can you post a picture of that bill? Without any identifying info or anything like that. 9 CCFs shouldn't be $200. Maybe $20.

Josh342

Josh342

@Hot_water_fan Yeah, I should have looked closer. 249 CCF / 1.037 = 240.16 therms

bburd

That’s an average in Feb. of 8.6 CCF *per day*. Times 28 days equals 241 CCF for the entire month.

Josh342

Do those numbers seem high for my current usage?  I know that's a loaded question.  Lots of variables. 

bburd

I’m not sure where you live, but it seems reasonable to me for a house of that size.

Hot_water_fan

Do those numbers seem high for my current usage? I know that's a loaded question. Lots of variables.

Based on the usage it looks like about 36,000btu heat loss, so 30 btu/sqft. It's typical for an older house.

Josh342

I thought with such an old furnace that my usage would be much higher. 

offdutytech

Have you considered mini split heat pump for the second floor rooms. Each room would have its own head and one condensing unit outside. From a retro fit standpoint it might be easier based on your floor plan. For the first floor if you wanted you can do radiant heat more easily because you have access to the basement. 
For the first floor you can use an electric boiler if a gas condensing boiler is too large for that load unless you do an indirect hot water tank. . My preferred electric boiler we install for customers is Electro. Menards also has Thermo electric with are alright. 

https://electromn.com/electric-mini-boiler/

hot_rod

Josh342 said:

I thought with such an old furnace that my usage would be much higher. 

It depends on the heat load over those periods. The outdoor conditions, temperature and wind for example.
Adding a graph of temperatures below that usage graph would tell more of a story.

How you use the space also, doors opening and closing, cooking, dryer running, lights, assuming they are not on the same meter, even you giving off maybe 400 btu/ hr , all add to the heat within the home.

Hopefully you are not wishing for higher fuel consumption?

Josh342

@offdutytech I was thinking about doing a mini split originally. This was for the sake of having AC since I was unable to attach to my furnace. Then priority got in the way and I felt I should do something about the furnace.  The idea of doing a split mini upstairs isn't an opposing idea.  I'm open to what makes most sense.  I am not eager to be opening the walls and ceiling to run PEX but I feel as if it will be a necessary evil.  I am concerned about going electric for a boiler since natural gas is cheaper.  One advantage with electric is that I do not have to worry about venting outside. 

Josh342

@hot_rod No, I can't see why I would want a higher fuel consumption.  My biggest gripe right now is that my feet are always cold when I walk around my house.  There isn't good air circulation with this furnace. 

hot_rod

I know the feeling, I have lived in, currently do, a forced air home. I buy thicker and thicker sox trying to keep warm feet when sitting around. Nothing compares to properly designed and installed radiant floors for foot comfort. And peace and quiet heat😁

Josh342

So going back to the radiant idea on first floor, I came across a post on here from someone and @Gordy shared a document regarding the output of radiant flooring using the PEX method and based on the output vs my heat loss for living room, it appeared Iike, based on my calculations that it wouldn't be sufficient to heat.  Perhaps I calculated incorrectly. 

Josh342

Something else I just thought of, my current state of the second floor is that the heater duct is in Jonah's room. That is referenced in earlier where I gave the heat loss. Why they did this, I don't know. There is no other heater duct upstairs other than an open vent that is situated just past the stairs as you approach the second floor. The other two bedrooms always feel comfortable. So that makes me wonder, is it possible with radiant heat on the first floor that that would continue to occur. I know radiant tends to heat the area of where the individual is in relationship to the floor. But I know heat rises as well. Do you think my situation would still be the same? I think the idea of a mini split, perhaps just one on the second floor could be sufficient.

psb75

Radiant heat on the first floor seems magical , in the room that it is in. It heats everything in the room--not so much (or very well) the rooms where it ISN'T. Even the the floors above it--as in, the second floor--receive very little of the heat because radiant doesn't really create convection currents in the air. That is part of its marvel. Convection currents (or air moving over people's skin) tends to make them feel "cold."