DIY radiant heat system

[seayaker]

I'm exploring the possibility of making a radiant floor heating system for a RV or van with a propane tankless water heater. I've been using a 12 liter per min. heater in a RV for years and am very happy with it. I just wonder how efficient it would be if I got a water pump and some pex tubing and made a closed system. The heater seems to be very efficient for my hot water so I just wonder if it would be worth while to make a heat system. I like the idea of having the heater outside where no fumes would get in and pump the hot water through the tubing. Any thoughts on how efficient it could be. I'm not at the point to do mathematical calculations just looking for a semi educated guess.

 

[LittleInch]

Define "efficiency".

I think you might be confusing this with effectiveness, i.e. can it heat your RV to a temperature that you find comfortable.?

Different question.

Given most RV's are insulated like a paper bag, I think you'll be fortunate to get enough heat in without burning a cylinder a night....

It sounds like you're contemplating an under floor heating system? You will need very good insulation under it and a lot of square area as the temperature is limited to stop it burning your feet. An air coil might be abetter plan.

As ever some more details helps - power of heater, temperature of the water etc....

And "radiant" to me means infra red glowing type, not a water heater.

 

[EdStainless]

Colloquially hot floors in US are referred to radiant heating.
I doubt that you have enough floor area to effusively heat the entire RV.
You could make the floors a lot more comfortable in the winter though.
You would need to tear out the existing floor, at least the upper layers.
Put down a layer of high-density insulation, top it, add your tubes, and then build your finish floor around them.
You will be raising the floor by about 2-3".
Without the insulation more of your heat will go outdoors than indoors.

 

[seayaker]

Colloquially hot floors in US are referred to radiant heating.
I doubt that you have enough floor area to effusively heat the entire RV.
You could make the floors a lot more comfortable in the winter though.
You would need to tear out the existing floor, at least the upper layers.
Put down a layer of high-density insulation, top it, add your tubes, and then build your finish floor around them.
You will be raising the floor by about 2-3".
Without the insulation more of your heat will go outdoors than indoors.

Thanks for responding, I'm just kicking this around, there are several videos on you tube of van floor heating systems, even some company's making kits for sale. I live in a small RV and have for years, I built a small wood stove and it has worked great for years. I don't keep it going through the night though so I was thinking about how to make it a little warmer during the cold spells. I don't like any of the propane heaters and I would like to see if I could come up with something that would keep the combustion part the and pump outside and circulate the hot water either through floor or wall radiators. Would it be better to have radiators along the walls as apposed to in the floor? I have another tankless propane water heater, I would have to get a water pump, tubing and some kind of radiator to try it. Again just kicking it around to see if it's feasible. I appreciate any InSite or suggestions.

 

[LittleInch]

A radiator type heater would probably be far better, less invasive to install and operates at a similar temperature to your hot water system ( 60 to 70C).

But beware that a burner system designed for occasional hot water usage, may not be a good use for continuous heating and could very easily break or burn out if fired for long periods.

You probably also want a unit which modulates and not a simple on/ off unit.

There are no doubt many such small units available for the RV or boat / caravan / mobile home type set up. Last mobile home I stayed in had a small domestic boiler unit and radiators which ran off LPG. Very common now in mobile home parks.

This is but a simple example fo the range of heaters. https://www.thecaravanwarehouse.co.uk/Products/boilers--water-heaters I know it's UK based, but they exist everywhere.

 

[IFRs]

floor radiant heat does not penetrate carpet well, your feet might like carpet better anyway

 

[seayaker]

Thankyou, that's very helpful. The reason I thought about the tankless LPG heater is because I have an old one, also because of weight and space. I lived in a van for a few years and I may get another one. The climate here is fairly mild but it does freeze occasionally. Right now I live in a 17' trailer with a tiny wood stove that I built. I've used it for years. it's sealed and has an outside air intake so it doesn't use the oxygen in the camper. I've always wondered why a LPG heater couldn't be made like that. At least I don't know of any. the tankless water heater. When the hot water is turned on a it trips the sensor that turns the gas on and lights it. I take nice hot showers for 10-15 min. plus am constantly using hot water to wash my hands and dishes. I can't help wondering why it couldn't used for heat.
I can experiment with the old heater, if I can find a pump and a small radiator just to see how much heat it would produce and how much propane it would use. Ideas welcome.

 

[IRstuff]

I can't help wondering why it couldn't used for heat.

There are tankless water heaters that can be used for heating; they have a separate loop and separate pump that is controlled by the thermostat. However, the demand is substantially higher than that of hot water usage; imagine, say, a 15-minute hot shower every half hour, every night. That level of usage essentially means that the life/reliability of the water heater and pump is correspondingly decreased.

 

[dvd]

The heating load is really needed to determine how successful you may be in this study. Just assuming that you have a 10,000 BTU/hr heat load, and with an average caloric content of 20,000 BTU/lb, you would burn 0.5 lb/hr of propane. At $1/lb you would have a heating cost of 0.5 lb/hr x $1/lb x 24 hr/day = $12/day and you would burn 0.5 lb/hr x 24 hr/day = 12 lb/day. You would go through a 20 lb tank of propane every 1.67 days. I just guessed at a heating load, and simplified the caloric content to include some amount of efficiency on the heater. You would need to get into the specifics to see how palatable this would be for you. One issue that comes to mind is whether you could find a small enough unit to provide a somewhat steady load, or whether you would be cycling continually.

 

[seayaker]

The heating load is really needed to determine how successful you may be in this study. Just assuming that you have a 10,000 BTU/hr heat load, and with an average caloric content of 20,000 BTU/lb, you would burn 0.5 lb/hr of propane. At $1/lb you would have a heating cost of 0.5 lb/hr x $1/lb x 24 hr/day = $12/day and you would burn 0.5 lb/hr x 24 hr/day = 12 lb/day. You would go through a 20 lb tank of propane every 1.67 days. I just guessed at a heating load, and simplified the caloric content to include some amount of efficiency on the heater. You would need to get into the specifics to see how palatable this would be for you. One issue that comes to mind is whether you could find a small enough unit to provide a somewhat steady load, or whether you would be cycling continually.

Thankyou, that helps give me an idea of weather it would be worth it. I guess the question is how it would compare to any of the other propane heaters such as a Mr. heat or even a RV furnace. If it doesn't cost that much more to to heat a given space with it then it may be worth while. The advantage of not having to light a pilot or using up the oxygen in a small area.

 

[dvd]

You really need to assess the heating load to make any good decisions on this. You may find that investing in insulation will move you into more economical choices. Also, IF propane costs $1/lb at ~22,000 BTU/lb (=6.4 kW-hr --> $0.16/kW-hr ) then consider how that would compare with electrical heating, assuming that you have access to electric grid.

p.s. assuming your stage name seayaker indicates you are a paddler - me, too.

 

[LittleInch]

If you've got a heater that gives you a decent shower then it's probably at least 10kW / 35000 Btu/hr which is more than adequate to heat an RV/ caravan. One issue with using a water heater is that it is sized to heat cold water to maybe 60C, whereas a radiator type system will have return water coming back at 40 to 50C once the system warms up. Your heat load though is probably a lot lower, hence why you need a modulating boiler and also one sized for that return temp.

A system over sized will just short cycle itself to death.

One option you could look at maybe is getting a hot water thermal storage unit which slowly heats up to 90+C then you send water round it via a coil to extract the heat. You could even link it to your solid fuel fire or add a stove pipe heat exchanger. Then you could use a very low power heater to slowly heat this store up, or even use low power electricity at 1 to 2 kW for a few hours.

Small condensing boilers which have a balanced flue are your best bet by far.

 

[seayaker]

Thankyou, very helpful! I should explain this is a low budget DIY kind of project and I'm gathering information to see if it's even feasible. My RV has roughly 600 cubic ft of area to heat I usually only need to raise the temp. about 20 deg. F. I have a 12 liter per min. water heater and a propane stove for cooking and a 20 lb. tank (about $12 to fill) last's about a month in winter, That's cooking, showers and washing hands etc. I can get a 6 liter per min. tankless water heater for $70. I don't know if it's possible to make a closed loop system with just the heater, pump and heat exchanger but that would be best. The heater and pump would be isolated from the living area, (mostly outside). Quiet and no fumes are the main priority's. These heaters come on when the water starts flowing so if there was a temp controlled switch that would turn the pump on wouldn't that work? I don't know if there is a max. temp for incoming water. I believe about 120 deg F coming out to the exchanger is good, need a way to allow for expansion. Appreciate any advice or suggestions.

If you've got a heater that gives you a decent shower then it's probably at least 10kW / 35000 Btu/hr which is more than adequate to heat an RV/ caravan. One issue with using a water heater is that it is sized to heat cold water to maybe 60C, whereas a radiator type system will have return water coming back at 40 to 50C once the system warms up. Your heat load though is probably a lot lower, hence why you need a modulating boiler and also one sized for that return temp.

A system over sized will just short cycle itself to death.

One option you could look at maybe is getting a hot water thermal storage unit which slowly heats up to 90+C then you send water round it via a coil to extract the heat. You could even link it to your solid fuel fire or add a stove pipe heat exchanger. Then you could use a very low power heater to slowly heat this store up, or even use low power electricity at 1 to 2 kW for a few hours.

Small condensing boilers which have a balanced flue are your best bet by far.

 

[seayaker]

You really need to assess the heating load to make any good decisions on this. You may find that investing in insulation will move you into more economical choices. Also, IF propane costs $1/lb at ~22,000 BTU/lb (=6.4 kW-hr --> $0.16/kW-hr ) then consider how that would compare with electrical heating, assuming that you have access to electric grid.

p.s. assuming your stage name seayaker indicates you are a paddler - me, too.

Thanks, it's hard to find all the data to assess the heating load all I have so far is I'm heating about 600 cubic ft. about 20 deg F. I'll post more when I get more info. I am an avid ocean fishing kayaker every chance I get. I should also say I'm not an engineer, I'm 70 yrs old trying to prepare incase rent becomes unaffordable and I have to move into a van.